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| author | Indrajith K L | 2022-12-03 17:00:20 +0530 |
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| committer | Indrajith K L | 2022-12-03 17:00:20 +0530 |
| commit | f5c4671bfbad96bf346bd7e9a21fc4317b4959df (patch) | |
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diff --git a/ffmpeg/doc/faq.html b/ffmpeg/doc/faq.html new file mode 100644 index 0000000..ba23431 --- /dev/null +++ b/ffmpeg/doc/faq.html @@ -0,0 +1,823 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> +<html> +<!-- Created by GNU Texinfo 6.8, https://www.gnu.org/software/texinfo/ --> + <head> + <meta charset="utf-8"> + <title> + FFmpeg FAQ + </title> + <meta name="viewport" content="width=device-width,initial-scale=1.0"> + <link rel="stylesheet" type="text/css" href="bootstrap.min.css"> + <link rel="stylesheet" type="text/css" href="style.min.css"> + </head> + <body> + <div class="container"> + <h1> + FFmpeg FAQ + </h1> +<div align="center"> +</div> + + +<a name="SEC_Top"></a> + +<div class="Contents_element" id="SEC_Contents"> +<h2 class="contents-heading">Table of Contents</h2> + +<div class="contents"> + +<ul class="no-bullet"> + <li><a id="toc-General-Questions" href="#General-Questions">1 General Questions</a> + <ul class="no-bullet"> + <li><a id="toc-Why-doesn_0027t-FFmpeg-support-feature-_005bxyz_005d_003f" href="#Why-doesn_0027t-FFmpeg-support-feature-_005bxyz_005d_003f">1.1 Why doesn’t FFmpeg support feature [xyz]?</a></li> + <li><a id="toc-FFmpeg-does-not-support-codec-XXX_002e-Can-you-include-a-Windows-DLL-loader-to-support-it_003f" href="#FFmpeg-does-not-support-codec-XXX_002e-Can-you-include-a-Windows-DLL-loader-to-support-it_003f">1.2 FFmpeg does not support codec XXX. Can you include a Windows DLL loader to support it?</a></li> + <li><a id="toc-I-cannot-read-this-file-although-this-format-seems-to-be-supported-by-ffmpeg_002e" href="#I-cannot-read-this-file-although-this-format-seems-to-be-supported-by-ffmpeg_002e">1.3 I cannot read this file although this format seems to be supported by ffmpeg.</a></li> + <li><a id="toc-Which-codecs-are-supported-by-Windows_003f" href="#Which-codecs-are-supported-by-Windows_003f">1.4 Which codecs are supported by Windows?</a></li> + </ul></li> + <li><a id="toc-Compilation" href="#Compilation">2 Compilation</a> + <ul class="no-bullet"> + <li><a id="toc-error_003a-can_0027t-find-a-register-in-class-_0027GENERAL_005fREGS_0027-while-reloading-_0027asm_0027" href="#error_003a-can_0027t-find-a-register-in-class-_0027GENERAL_005fREGS_0027-while-reloading-_0027asm_0027">2.1 <code>error: can't find a register in class 'GENERAL_REGS' while reloading 'asm'</code></a></li> + <li><a id="toc-I-have-installed-this-library-with-my-distro_0027s-package-manager_002e-Why-does-configure-not-see-it_003f" href="#I-have-installed-this-library-with-my-distro_0027s-package-manager_002e-Why-does-configure-not-see-it_003f">2.2 I have installed this library with my distro’s package manager. Why does <code>configure</code> not see it?</a></li> + <li><a id="toc-How-do-I-make-pkg_002dconfig-find-my-libraries_003f" href="#How-do-I-make-pkg_002dconfig-find-my-libraries_003f">2.3 How do I make <code>pkg-config</code> find my libraries?</a></li> + <li><a id="toc-How-do-I-use-pkg_002dconfig-when-cross_002dcompiling_003f" href="#How-do-I-use-pkg_002dconfig-when-cross_002dcompiling_003f">2.4 How do I use <code>pkg-config</code> when cross-compiling?</a></li> + </ul></li> + <li><a id="toc-Usage" href="#Usage">3 Usage</a> + <ul class="no-bullet"> + <li><a id="toc-ffmpeg-does-not-work_003b-what-is-wrong_003f" href="#ffmpeg-does-not-work_003b-what-is-wrong_003f">3.1 ffmpeg does not work; what is wrong?</a></li> + <li><a id="toc-How-do-I-encode-single-pictures-into-movies_003f" href="#How-do-I-encode-single-pictures-into-movies_003f">3.2 How do I encode single pictures into movies?</a></li> + <li><a id="toc-How-do-I-encode-movie-to-single-pictures_003f" href="#How-do-I-encode-movie-to-single-pictures_003f">3.3 How do I encode movie to single pictures?</a></li> + <li><a id="toc-Why-do-I-see-a-slight-quality-degradation-with-multithreaded-MPEG_002a-encoding_003f" href="#Why-do-I-see-a-slight-quality-degradation-with-multithreaded-MPEG_002a-encoding_003f">3.4 Why do I see a slight quality degradation with multithreaded MPEG* encoding?</a></li> + <li><a id="toc-How-can-I-read-from-the-standard-input-or-write-to-the-standard-output_003f" href="#How-can-I-read-from-the-standard-input-or-write-to-the-standard-output_003f">3.5 How can I read from the standard input or write to the standard output?</a></li> + <li><a id="toc-_002df-jpeg-doesn_0027t-work_002e" href="#g_t_002df-jpeg-doesn_0027t-work_002e">3.6 -f jpeg doesn’t work.</a></li> + <li><a id="toc-Why-can-I-not-change-the-frame-rate_003f" href="#Why-can-I-not-change-the-frame-rate_003f">3.7 Why can I not change the frame rate?</a></li> + <li><a id="toc-How-do-I-encode-Xvid-or-DivX-video-with-ffmpeg_003f" href="#How-do-I-encode-Xvid-or-DivX-video-with-ffmpeg_003f">3.8 How do I encode Xvid or DivX video with ffmpeg?</a></li> + <li><a id="toc-Which-are-good-parameters-for-encoding-high-quality-MPEG_002d4_003f" href="#Which-are-good-parameters-for-encoding-high-quality-MPEG_002d4_003f">3.9 Which are good parameters for encoding high quality MPEG-4?</a></li> + <li><a id="toc-Which-are-good-parameters-for-encoding-high-quality-MPEG_002d1_002fMPEG_002d2_003f" href="#Which-are-good-parameters-for-encoding-high-quality-MPEG_002d1_002fMPEG_002d2_003f">3.10 Which are good parameters for encoding high quality MPEG-1/MPEG-2?</a></li> + <li><a id="toc-Interlaced-video-looks-very-bad-when-encoded-with-ffmpeg_002c-what-is-wrong_003f" href="#Interlaced-video-looks-very-bad-when-encoded-with-ffmpeg_002c-what-is-wrong_003f">3.11 Interlaced video looks very bad when encoded with ffmpeg, what is wrong?</a></li> + <li><a id="toc-How-can-I-read-DirectShow-files_003f" href="#How-can-I-read-DirectShow-files_003f">3.12 How can I read DirectShow files?</a></li> + <li><a id="toc-How-can-I-join-video-files_003f" href="#How-can-I-join-video-files_003f">3.13 How can I join video files?</a></li> + <li><a id="toc-How-can-I-concatenate-video-files_003f" href="#How-can-I-concatenate-video-files_003f">3.14 How can I concatenate video files?</a> + <ul class="no-bullet"> + <li><a id="toc-Concatenating-using-the-concat-filter" href="#Concatenating-using-the-concat-filter">3.14.1 Concatenating using the concat <em>filter</em></a></li> + <li><a id="toc-Concatenating-using-the-concat-demuxer" href="#Concatenating-using-the-concat-demuxer">3.14.2 Concatenating using the concat <em>demuxer</em></a></li> + <li><a id="toc-Concatenating-using-the-concat-protocol-_0028file-level_0029" href="#Concatenating-using-the-concat-protocol-_0028file-level_0029">3.14.3 Concatenating using the concat <em>protocol</em> (file level)</a></li> + <li><a id="toc-Concatenating-using-raw-audio-and-video" href="#Concatenating-using-raw-audio-and-video">3.14.4 Concatenating using raw audio and video</a></li> + </ul></li> + <li><a id="toc-Using-_002df-lavfi_002c-audio-becomes-mono-for-no-apparent-reason_002e" href="#Using-_002df-lavfi_002c-audio-becomes-mono-for-no-apparent-reason_002e">3.15 Using <samp>-f lavfi</samp>, audio becomes mono for no apparent reason.</a></li> + <li><a id="toc-Why-does-FFmpeg-not-see-the-subtitles-in-my-VOB-file_003f" href="#Why-does-FFmpeg-not-see-the-subtitles-in-my-VOB-file_003f">3.16 Why does FFmpeg not see the subtitles in my VOB file?</a></li> + <li><a id="toc-Why-was-the-ffmpeg-_002dsameq-option-removed_003f-What-to-use-instead_003f" href="#Why-was-the-ffmpeg-_002dsameq-option-removed_003f-What-to-use-instead_003f">3.17 Why was the <code>ffmpeg</code> <samp>-sameq</samp> option removed? What to use instead?</a></li> + <li><a id="toc-I-have-a-stretched-video_002c-why-does-scaling-does-not-fix-it_003f" href="#I-have-a-stretched-video_002c-why-does-scaling-does-not-fix-it_003f">3.18 I have a stretched video, why does scaling does not fix it?</a></li> + <li><a id="toc-How-do-I-run-ffmpeg-as-a-background-task_003f" href="#How-do-I-run-ffmpeg-as-a-background-task_003f">3.19 How do I run ffmpeg as a background task?</a></li> + <li><a id="toc-How-do-I-prevent-ffmpeg-from-suspending-with-a-message-like-suspended-_0028tty-output_0029_003f" href="#How-do-I-prevent-ffmpeg-from-suspending-with-a-message-like-suspended-_0028tty-output_0029_003f">3.20 How do I prevent ffmpeg from suspending with a message like <em>suspended (tty output)</em>?</a></li> + </ul></li> + <li><a id="toc-Development" href="#Development">4 Development</a> + <ul class="no-bullet"> + <li><a id="toc-Are-there-examples-illustrating-how-to-use-the-FFmpeg-libraries_002c-particularly-libavcodec-and-libavformat_003f" href="#Are-there-examples-illustrating-how-to-use-the-FFmpeg-libraries_002c-particularly-libavcodec-and-libavformat_003f">4.1 Are there examples illustrating how to use the FFmpeg libraries, particularly libavcodec and libavformat?</a></li> + <li><a id="toc-Can-you-support-my-C-compiler-XXX_003f" href="#Can-you-support-my-C-compiler-XXX_003f">4.2 Can you support my C compiler XXX?</a></li> + <li><a id="toc-Is-Microsoft-Visual-C_002b_002b-supported_003f" href="#Is-Microsoft-Visual-C_002b_002b-supported_003f">4.3 Is Microsoft Visual C++ supported?</a></li> + <li><a id="toc-Can-you-add-automake_002c-libtool-or-autoconf-support_003f" href="#Can-you-add-automake_002c-libtool-or-autoconf-support_003f">4.4 Can you add automake, libtool or autoconf support?</a></li> + <li><a id="toc-Why-not-rewrite-FFmpeg-in-object_002doriented-C_002b_002b_003f" href="#Why-not-rewrite-FFmpeg-in-object_002doriented-C_002b_002b_003f">4.5 Why not rewrite FFmpeg in object-oriented C++?</a></li> + <li><a id="toc-Why-are-the-ffmpeg-programs-devoid-of-debugging-symbols_003f" href="#Why-are-the-ffmpeg-programs-devoid-of-debugging-symbols_003f">4.6 Why are the ffmpeg programs devoid of debugging symbols?</a></li> + <li><a id="toc-I-do-not-like-the-LGPL_002c-can-I-contribute-code-under-the-GPL-instead_003f" href="#I-do-not-like-the-LGPL_002c-can-I-contribute-code-under-the-GPL-instead_003f">4.7 I do not like the LGPL, can I contribute code under the GPL instead?</a></li> + <li><a id="toc-I_0027m-using-FFmpeg-from-within-my-C-application-but-the-linker-complains-about-missing-symbols-from-the-libraries-themselves_002e" href="#I_0027m-using-FFmpeg-from-within-my-C-application-but-the-linker-complains-about-missing-symbols-from-the-libraries-themselves_002e">4.8 I’m using FFmpeg from within my C application but the linker complains about missing symbols from the libraries themselves.</a></li> + <li><a id="toc-I_0027m-using-FFmpeg-from-within-my-C_002b_002b-application-but-the-linker-complains-about-missing-symbols-which-seem-to-be-available_002e" href="#I_0027m-using-FFmpeg-from-within-my-C_002b_002b-application-but-the-linker-complains-about-missing-symbols-which-seem-to-be-available_002e">4.9 I’m using FFmpeg from within my C++ application but the linker complains about missing symbols which seem to be available.</a></li> + <li><a id="toc-I_0027m-using-libavutil-from-within-my-C_002b_002b-application-but-the-compiler-complains-about-_0027UINT64_005fC_0027-was-not-declared-in-this-scope" href="#I_0027m-using-libavutil-from-within-my-C_002b_002b-application-but-the-compiler-complains-about-_0027UINT64_005fC_0027-was-not-declared-in-this-scope">4.10 I’m using libavutil from within my C++ application but the compiler complains about ’UINT64_C’ was not declared in this scope</a></li> + <li><a id="toc-I-have-a-file-in-memory-_002f-a-API-different-from-_002aopen_002f_002aread_002f-libc-how-do-I-use-it-with-libavformat_003f" href="#I-have-a-file-in-memory-_002f-a-API-different-from-_002aopen_002f_002aread_002f-libc-how-do-I-use-it-with-libavformat_003f">4.11 I have a file in memory / a API different from *open/*read/ libc how do I use it with libavformat?</a></li> + <li><a id="toc-Where-is-the-documentation-about-ffv1_002c-msmpeg4_002c-asv1_002c-4xm_003f" href="#Where-is-the-documentation-about-ffv1_002c-msmpeg4_002c-asv1_002c-4xm_003f">4.12 Where is the documentation about ffv1, msmpeg4, asv1, 4xm?</a></li> + <li><a id="toc-How-do-I-feed-H_002e263_002dRTP-_0028and-other-codecs-in-RTP_0029-to-libavcodec_003f" href="#How-do-I-feed-H_002e263_002dRTP-_0028and-other-codecs-in-RTP_0029-to-libavcodec_003f">4.13 How do I feed H.263-RTP (and other codecs in RTP) to libavcodec?</a></li> + <li><a id="toc-AVStream_002er_005fframe_005frate-is-wrong_002c-it-is-much-larger-than-the-frame-rate_002e" href="#AVStream_002er_005fframe_005frate-is-wrong_002c-it-is-much-larger-than-the-frame-rate_002e">4.14 AVStream.r_frame_rate is wrong, it is much larger than the frame rate.</a></li> + <li><a id="toc-Why-is-make-fate-not-running-all-tests_003f" href="#Why-is-make-fate-not-running-all-tests_003f">4.15 Why is <code>make fate</code> not running all tests?</a></li> + <li><a id="toc-Why-is-make-fate-not-finding-the-samples_003f" href="#Why-is-make-fate-not-finding-the-samples_003f">4.16 Why is <code>make fate</code> not finding the samples?</a></li> + </ul></li> +</ul> +</div> +</div> + +<a name="General-Questions"></a> +<h2 class="chapter">1 General Questions<span class="pull-right"><a class="anchor hidden-xs" href="#General-Questions" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-General-Questions" aria-hidden="true">TOC</a></span></h2> + +<a name="Why-doesn_0027t-FFmpeg-support-feature-_005bxyz_005d_003f"></a> +<h3 class="section">1.1 Why doesn’t FFmpeg support feature [xyz]?<span class="pull-right"><a class="anchor hidden-xs" href="#Why-doesn_0027t-FFmpeg-support-feature-_005bxyz_005d_003f" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-Why-doesn_0027t-FFmpeg-support-feature-_005bxyz_005d_003f" aria-hidden="true">TOC</a></span></h3> + +<p>Because no one has taken on that task yet. FFmpeg development is +driven by the tasks that are important to the individual developers. +If there is a feature that is important to you, the best way to get +it implemented is to undertake the task yourself or sponsor a developer. +</p> +<a name="FFmpeg-does-not-support-codec-XXX_002e-Can-you-include-a-Windows-DLL-loader-to-support-it_003f"></a> +<h3 class="section">1.2 FFmpeg does not support codec XXX. Can you include a Windows DLL loader to support it?<span class="pull-right"><a class="anchor hidden-xs" href="#FFmpeg-does-not-support-codec-XXX_002e-Can-you-include-a-Windows-DLL-loader-to-support-it_003f" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-FFmpeg-does-not-support-codec-XXX_002e-Can-you-include-a-Windows-DLL-loader-to-support-it_003f" aria-hidden="true">TOC</a></span></h3> + +<p>No. Windows DLLs are not portable, bloated and often slow. +Moreover FFmpeg strives to support all codecs natively. +A DLL loader is not conducive to that goal. +</p> +<a name="I-cannot-read-this-file-although-this-format-seems-to-be-supported-by-ffmpeg_002e"></a> +<h3 class="section">1.3 I cannot read this file although this format seems to be supported by ffmpeg.<span class="pull-right"><a class="anchor hidden-xs" href="#I-cannot-read-this-file-although-this-format-seems-to-be-supported-by-ffmpeg_002e" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-I-cannot-read-this-file-although-this-format-seems-to-be-supported-by-ffmpeg_002e" aria-hidden="true">TOC</a></span></h3> + +<p>Even if ffmpeg can read the container format, it may not support all its +codecs. Please consult the supported codec list in the ffmpeg +documentation. +</p> +<a name="Which-codecs-are-supported-by-Windows_003f"></a> +<h3 class="section">1.4 Which codecs are supported by Windows?<span class="pull-right"><a class="anchor hidden-xs" href="#Which-codecs-are-supported-by-Windows_003f" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-Which-codecs-are-supported-by-Windows_003f" aria-hidden="true">TOC</a></span></h3> + +<p>Windows does not support standard formats like MPEG very well, unless you +install some additional codecs. +</p> +<p>The following list of video codecs should work on most Windows systems: +</p><dl compact="compact"> +<dt><span><samp>msmpeg4v2</samp></span></dt> +<dd><p>.avi/.asf +</p></dd> +<dt><span><samp>msmpeg4</samp></span></dt> +<dd><p>.asf only +</p></dd> +<dt><span><samp>wmv1</samp></span></dt> +<dd><p>.asf only +</p></dd> +<dt><span><samp>wmv2</samp></span></dt> +<dd><p>.asf only +</p></dd> +<dt><span><samp>mpeg4</samp></span></dt> +<dd><p>Only if you have some MPEG-4 codec like ffdshow or Xvid installed. +</p></dd> +<dt><span><samp>mpeg1video</samp></span></dt> +<dd><p>.mpg only +</p></dd> +</dl> +<p>Note, ASF files often have .wmv or .wma extensions in Windows. It should also +be mentioned that Microsoft claims a patent on the ASF format, and may sue +or threaten users who create ASF files with non-Microsoft software. It is +strongly advised to avoid ASF where possible. +</p> +<p>The following list of audio codecs should work on most Windows systems: +</p><dl compact="compact"> +<dt><span><samp>adpcm_ima_wav</samp></span></dt> +<dt><span><samp>adpcm_ms</samp></span></dt> +<dt><span><samp>pcm_s16le</samp></span></dt> +<dd><p>always +</p></dd> +<dt><span><samp>libmp3lame</samp></span></dt> +<dd><p>If some MP3 codec like LAME is installed. +</p></dd> +</dl> + + +<a name="Compilation"></a> +<h2 class="chapter">2 Compilation<span class="pull-right"><a class="anchor hidden-xs" href="#Compilation" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-Compilation" aria-hidden="true">TOC</a></span></h2> + +<a name="error_003a-can_0027t-find-a-register-in-class-_0027GENERAL_005fREGS_0027-while-reloading-_0027asm_0027"></a> +<h3 class="section">2.1 <code>error: can't find a register in class 'GENERAL_REGS' while reloading 'asm'</code><span class="pull-right"><a class="anchor hidden-xs" href="#error_003a-can_0027t-find-a-register-in-class-_0027GENERAL_005fREGS_0027-while-reloading-_0027asm_0027" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-error_003a-can_0027t-find-a-register-in-class-_0027GENERAL_005fREGS_0027-while-reloading-_0027asm_0027" aria-hidden="true">TOC</a></span></h3> + +<p>This is a bug in gcc. Do not report it to us. Instead, please report it to +the gcc developers. Note that we will not add workarounds for gcc bugs. +</p> +<p>Also note that (some of) the gcc developers believe this is not a bug or +not a bug they should fix: +<a href="https://gcc.gnu.org/bugzilla/show_bug.cgi?id=11203">https://gcc.gnu.org/bugzilla/show_bug.cgi?id=11203</a>. +Then again, some of them do not know the difference between an undecidable +problem and an NP-hard problem... +</p> +<a name="I-have-installed-this-library-with-my-distro_0027s-package-manager_002e-Why-does-configure-not-see-it_003f"></a> +<h3 class="section">2.2 I have installed this library with my distro’s package manager. Why does <code>configure</code> not see it?<span class="pull-right"><a class="anchor hidden-xs" href="#I-have-installed-this-library-with-my-distro_0027s-package-manager_002e-Why-does-configure-not-see-it_003f" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-I-have-installed-this-library-with-my-distro_0027s-package-manager_002e-Why-does-configure-not-see-it_003f" aria-hidden="true">TOC</a></span></h3> + +<p>Distributions usually split libraries in several packages. The main package +contains the files necessary to run programs using the library. The +development package contains the files necessary to build programs using the +library. Sometimes, docs and/or data are in a separate package too. +</p> +<p>To build FFmpeg, you need to install the development package. It is usually +called <samp>libfoo-dev</samp> or <samp>libfoo-devel</samp>. You can remove it after the +build is finished, but be sure to keep the main package. +</p> +<a name="How-do-I-make-pkg_002dconfig-find-my-libraries_003f"></a> +<h3 class="section">2.3 How do I make <code>pkg-config</code> find my libraries?<span class="pull-right"><a class="anchor hidden-xs" href="#How-do-I-make-pkg_002dconfig-find-my-libraries_003f" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-How-do-I-make-pkg_002dconfig-find-my-libraries_003f" aria-hidden="true">TOC</a></span></h3> + +<p>Somewhere along with your libraries, there is a <samp>.pc</samp> file (or several) +in a <samp>pkgconfig</samp> directory. You need to set environment variables to +point <code>pkg-config</code> to these files. +</p> +<p>If you need to <em>add</em> directories to <code>pkg-config</code>’s search list +(typical use case: library installed separately), add it to +<code>$PKG_CONFIG_PATH</code>: +</p> +<div class="example"> +<pre class="example">export PKG_CONFIG_PATH=/opt/x264/lib/pkgconfig:/opt/opus/lib/pkgconfig +</pre></div> + +<p>If you need to <em>replace</em> <code>pkg-config</code>’s search list +(typical use case: cross-compiling), set it in +<code>$PKG_CONFIG_LIBDIR</code>: +</p> +<div class="example"> +<pre class="example">export PKG_CONFIG_LIBDIR=/home/me/cross/usr/lib/pkgconfig:/home/me/cross/usr/local/lib/pkgconfig +</pre></div> + +<p>If you need to know the library’s internal dependencies (typical use: static +linking), add the <code>--static</code> option to <code>pkg-config</code>: +</p> +<div class="example"> +<pre class="example">./configure --pkg-config-flags=--static +</pre></div> + +<a name="How-do-I-use-pkg_002dconfig-when-cross_002dcompiling_003f"></a> +<h3 class="section">2.4 How do I use <code>pkg-config</code> when cross-compiling?<span class="pull-right"><a class="anchor hidden-xs" href="#How-do-I-use-pkg_002dconfig-when-cross_002dcompiling_003f" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-How-do-I-use-pkg_002dconfig-when-cross_002dcompiling_003f" aria-hidden="true">TOC</a></span></h3> + +<p>The best way is to install <code>pkg-config</code> in your cross-compilation +environment. It will automatically use the cross-compilation libraries. +</p> +<p>You can also use <code>pkg-config</code> from the host environment by +specifying explicitly <code>--pkg-config=pkg-config</code> to <code>configure</code>. +In that case, you must point <code>pkg-config</code> to the correct directories +using the <code>PKG_CONFIG_LIBDIR</code>, as explained in the previous entry. +</p> +<p>As an intermediate solution, you can place in your cross-compilation +environment a script that calls the host <code>pkg-config</code> with +<code>PKG_CONFIG_LIBDIR</code> set. That script can look like that: +</p> +<div class="example"> +<pre class="example">#!/bin/sh +PKG_CONFIG_LIBDIR=/path/to/cross/lib/pkgconfig +export PKG_CONFIG_LIBDIR +exec /usr/bin/pkg-config "$@" +</pre></div> + +<a name="Usage"></a> +<h2 class="chapter">3 Usage<span class="pull-right"><a class="anchor hidden-xs" href="#Usage" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-Usage" aria-hidden="true">TOC</a></span></h2> + +<a name="ffmpeg-does-not-work_003b-what-is-wrong_003f"></a> +<h3 class="section">3.1 ffmpeg does not work; what is wrong?<span class="pull-right"><a class="anchor hidden-xs" href="#ffmpeg-does-not-work_003b-what-is-wrong_003f" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-ffmpeg-does-not-work_003b-what-is-wrong_003f" aria-hidden="true">TOC</a></span></h3> + +<p>Try a <code>make distclean</code> in the ffmpeg source directory before the build. +If this does not help see +(<a href="https://ffmpeg.org/bugreports.html">https://ffmpeg.org/bugreports.html</a>). +</p> +<a name="How-do-I-encode-single-pictures-into-movies_003f"></a> +<h3 class="section">3.2 How do I encode single pictures into movies?<span class="pull-right"><a class="anchor hidden-xs" href="#How-do-I-encode-single-pictures-into-movies_003f" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-How-do-I-encode-single-pictures-into-movies_003f" aria-hidden="true">TOC</a></span></h3> + +<p>First, rename your pictures to follow a numerical sequence. +For example, img1.jpg, img2.jpg, img3.jpg,... +Then you may run: +</p> +<div class="example"> +<pre class="example">ffmpeg -f image2 -i img%d.jpg /tmp/a.mpg +</pre></div> + +<p>Notice that ‘<samp>%d</samp>’ is replaced by the image number. +</p> +<p><samp>img%03d.jpg</samp> means the sequence <samp>img001.jpg</samp>, <samp>img002.jpg</samp>, etc. +</p> +<p>Use the <samp>-start_number</samp> option to declare a starting number for +the sequence. This is useful if your sequence does not start with +<samp>img001.jpg</samp> but is still in a numerical order. The following +example will start with <samp>img100.jpg</samp>: +</p> +<div class="example"> +<pre class="example">ffmpeg -f image2 -start_number 100 -i img%d.jpg /tmp/a.mpg +</pre></div> + +<p>If you have large number of pictures to rename, you can use the +following command to ease the burden. The command, using the bourne +shell syntax, symbolically links all files in the current directory +that match <code>*jpg</code> to the <samp>/tmp</samp> directory in the sequence of +<samp>img001.jpg</samp>, <samp>img002.jpg</samp> and so on. +</p> +<div class="example"> +<pre class="example">x=1; for i in *jpg; do counter=$(printf %03d $x); ln -s "$i" /tmp/img"$counter".jpg; x=$(($x+1)); done +</pre></div> + +<p>If you want to sequence them by oldest modified first, substitute +<code>$(ls -r -t *jpg)</code> in place of <code>*jpg</code>. +</p> +<p>Then run: +</p> +<div class="example"> +<pre class="example">ffmpeg -f image2 -i /tmp/img%03d.jpg /tmp/a.mpg +</pre></div> + +<p>The same logic is used for any image format that ffmpeg reads. +</p> +<p>You can also use <code>cat</code> to pipe images to ffmpeg: +</p> +<div class="example"> +<pre class="example">cat *.jpg | ffmpeg -f image2pipe -c:v mjpeg -i - output.mpg +</pre></div> + +<a name="How-do-I-encode-movie-to-single-pictures_003f"></a> +<h3 class="section">3.3 How do I encode movie to single pictures?<span class="pull-right"><a class="anchor hidden-xs" href="#How-do-I-encode-movie-to-single-pictures_003f" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-How-do-I-encode-movie-to-single-pictures_003f" aria-hidden="true">TOC</a></span></h3> + +<p>Use: +</p> +<div class="example"> +<pre class="example">ffmpeg -i movie.mpg movie%d.jpg +</pre></div> + +<p>The <samp>movie.mpg</samp> used as input will be converted to +<samp>movie1.jpg</samp>, <samp>movie2.jpg</samp>, etc... +</p> +<p>Instead of relying on file format self-recognition, you may also use +</p><dl compact="compact"> +<dt><span><samp>-c:v ppm</samp></span></dt> +<dt><span><samp>-c:v png</samp></span></dt> +<dt><span><samp>-c:v mjpeg</samp></span></dt> +</dl> +<p>to force the encoding. +</p> +<p>Applying that to the previous example: +</p><div class="example"> +<pre class="example">ffmpeg -i movie.mpg -f image2 -c:v mjpeg menu%d.jpg +</pre></div> + +<p>Beware that there is no "jpeg" codec. Use "mjpeg" instead. +</p> +<a name="Why-do-I-see-a-slight-quality-degradation-with-multithreaded-MPEG_002a-encoding_003f"></a> +<h3 class="section">3.4 Why do I see a slight quality degradation with multithreaded MPEG* encoding?<span class="pull-right"><a class="anchor hidden-xs" href="#Why-do-I-see-a-slight-quality-degradation-with-multithreaded-MPEG_002a-encoding_003f" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-Why-do-I-see-a-slight-quality-degradation-with-multithreaded-MPEG_002a-encoding_003f" aria-hidden="true">TOC</a></span></h3> + +<p>For multithreaded MPEG* encoding, the encoded slices must be independent, +otherwise thread n would practically have to wait for n-1 to finish, so it’s +quite logical that there is a small reduction of quality. This is not a bug. +</p> +<a name="How-can-I-read-from-the-standard-input-or-write-to-the-standard-output_003f"></a> +<h3 class="section">3.5 How can I read from the standard input or write to the standard output?<span class="pull-right"><a class="anchor hidden-xs" href="#How-can-I-read-from-the-standard-input-or-write-to-the-standard-output_003f" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-How-can-I-read-from-the-standard-input-or-write-to-the-standard-output_003f" aria-hidden="true">TOC</a></span></h3> + +<p>Use <samp>-</samp> as file name. +</p> +<a name="g_t_002df-jpeg-doesn_0027t-work_002e"></a> +<h3 class="section">3.6 -f jpeg doesn’t work.<span class="pull-right"><a class="anchor hidden-xs" href="#_002df-jpeg-doesn_0027t-work_002e" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-_002df-jpeg-doesn_0027t-work_002e" aria-hidden="true">TOC</a></span></h3> + +<p>Try ’-f image2 test%d.jpg’. +</p> +<a name="Why-can-I-not-change-the-frame-rate_003f"></a> +<h3 class="section">3.7 Why can I not change the frame rate?<span class="pull-right"><a class="anchor hidden-xs" href="#Why-can-I-not-change-the-frame-rate_003f" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-Why-can-I-not-change-the-frame-rate_003f" aria-hidden="true">TOC</a></span></h3> + +<p>Some codecs, like MPEG-1/2, only allow a small number of fixed frame rates. +Choose a different codec with the -c:v command line option. +</p> +<a name="How-do-I-encode-Xvid-or-DivX-video-with-ffmpeg_003f"></a> +<h3 class="section">3.8 How do I encode Xvid or DivX video with ffmpeg?<span class="pull-right"><a class="anchor hidden-xs" href="#How-do-I-encode-Xvid-or-DivX-video-with-ffmpeg_003f" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-How-do-I-encode-Xvid-or-DivX-video-with-ffmpeg_003f" aria-hidden="true">TOC</a></span></h3> + +<p>Both Xvid and DivX (version 4+) are implementations of the ISO MPEG-4 +standard (note that there are many other coding formats that use this +same standard). Thus, use ’-c:v mpeg4’ to encode in these formats. The +default fourcc stored in an MPEG-4-coded file will be ’FMP4’. If you want +a different fourcc, use the ’-vtag’ option. E.g., ’-vtag xvid’ will +force the fourcc ’xvid’ to be stored as the video fourcc rather than the +default. +</p> +<a name="Which-are-good-parameters-for-encoding-high-quality-MPEG_002d4_003f"></a> +<h3 class="section">3.9 Which are good parameters for encoding high quality MPEG-4?<span class="pull-right"><a class="anchor hidden-xs" href="#Which-are-good-parameters-for-encoding-high-quality-MPEG_002d4_003f" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-Which-are-good-parameters-for-encoding-high-quality-MPEG_002d4_003f" aria-hidden="true">TOC</a></span></h3> + +<p>’-mbd rd -flags +mv4+aic -trellis 2 -cmp 2 -subcmp 2 -g 300 -pass 1/2’, +things to try: ’-bf 2’, ’-mpv_flags qp_rd’, ’-mpv_flags mv0’, ’-mpv_flags skip_rd’. +</p> +<a name="Which-are-good-parameters-for-encoding-high-quality-MPEG_002d1_002fMPEG_002d2_003f"></a> +<h3 class="section">3.10 Which are good parameters for encoding high quality MPEG-1/MPEG-2?<span class="pull-right"><a class="anchor hidden-xs" href="#Which-are-good-parameters-for-encoding-high-quality-MPEG_002d1_002fMPEG_002d2_003f" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-Which-are-good-parameters-for-encoding-high-quality-MPEG_002d1_002fMPEG_002d2_003f" aria-hidden="true">TOC</a></span></h3> + +<p>’-mbd rd -trellis 2 -cmp 2 -subcmp 2 -g 100 -pass 1/2’ +but beware the ’-g 100’ might cause problems with some decoders. +Things to try: ’-bf 2’, ’-mpv_flags qp_rd’, ’-mpv_flags mv0’, ’-mpv_flags skip_rd’. +</p> +<a name="Interlaced-video-looks-very-bad-when-encoded-with-ffmpeg_002c-what-is-wrong_003f"></a> +<h3 class="section">3.11 Interlaced video looks very bad when encoded with ffmpeg, what is wrong?<span class="pull-right"><a class="anchor hidden-xs" href="#Interlaced-video-looks-very-bad-when-encoded-with-ffmpeg_002c-what-is-wrong_003f" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-Interlaced-video-looks-very-bad-when-encoded-with-ffmpeg_002c-what-is-wrong_003f" aria-hidden="true">TOC</a></span></h3> + +<p>You should use ’-flags +ilme+ildct’ and maybe ’-flags +alt’ for interlaced +material, and try ’-top 0/1’ if the result looks really messed-up. +</p> +<a name="How-can-I-read-DirectShow-files_003f"></a> +<h3 class="section">3.12 How can I read DirectShow files?<span class="pull-right"><a class="anchor hidden-xs" href="#How-can-I-read-DirectShow-files_003f" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-How-can-I-read-DirectShow-files_003f" aria-hidden="true">TOC</a></span></h3> + +<p>If you have built FFmpeg with <code>./configure --enable-avisynth</code> +(only possible on MinGW/Cygwin platforms), +then you may use any file that DirectShow can read as input. +</p> +<p>Just create an "input.avs" text file with this single line ... +</p><div class="example"> +<pre class="example">DirectShowSource("C:\path to your file\yourfile.asf") +</pre></div> +<p>... and then feed that text file to ffmpeg: +</p><div class="example"> +<pre class="example">ffmpeg -i input.avs +</pre></div> + +<p>For ANY other help on AviSynth, please visit the +<a href="http://www.avisynth.org/">AviSynth homepage</a>. +</p> +<a name="How-can-I-join-video-files_003f"></a> +<h3 class="section">3.13 How can I join video files?<span class="pull-right"><a class="anchor hidden-xs" href="#How-can-I-join-video-files_003f" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-How-can-I-join-video-files_003f" aria-hidden="true">TOC</a></span></h3> + +<p>To "join" video files is quite ambiguous. The following list explains the +different kinds of "joining" and points out how those are addressed in +FFmpeg. To join video files may mean: +</p> +<ul> +<li> To put them one after the other: this is called to <em>concatenate</em> them +(in short: concat) and is addressed +<a href="#How-can-I-concatenate-video-files">in this very faq</a>. + +</li><li> To put them together in the same file, to let the user choose between the +different versions (example: different audio languages): this is called to +<em>multiplex</em> them together (in short: mux), and is done by simply +invoking ffmpeg with several <samp>-i</samp> options. + +</li><li> For audio, to put all channels together in a single stream (example: two +mono streams into one stereo stream): this is sometimes called to +<em>merge</em> them, and can be done using the +<a href="ffmpeg-filters.html#amerge"><code>amerge</code></a> filter. + +</li><li> For audio, to play one on top of the other: this is called to <em>mix</em> +them, and can be done by first merging them into a single stream and then +using the <a href="ffmpeg-filters.html#pan"><code>pan</code></a> filter to mix +the channels at will. + +</li><li> For video, to display both together, side by side or one on top of a part of +the other; it can be done using the +<a href="ffmpeg-filters.html#overlay"><code>overlay</code></a> video filter. + +</li></ul> + +<span id="How-can-I-concatenate-video-files"></span><a name="How-can-I-concatenate-video-files_003f"></a> +<h3 class="section">3.14 How can I concatenate video files?<span class="pull-right"><a class="anchor hidden-xs" href="#How-can-I-concatenate-video-files_003f" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-How-can-I-concatenate-video-files_003f" aria-hidden="true">TOC</a></span></h3> + +<p>There are several solutions, depending on the exact circumstances. +</p> +<a name="Concatenating-using-the-concat-filter"></a> +<h4 class="subsection">3.14.1 Concatenating using the concat <em>filter</em><span class="pull-right"><a class="anchor hidden-xs" href="#Concatenating-using-the-concat-filter" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-Concatenating-using-the-concat-filter" aria-hidden="true">TOC</a></span></h4> + +<p>FFmpeg has a <a href="ffmpeg-filters.html#concat"><code>concat</code></a> filter designed specifically for that, with examples in the +documentation. This operation is recommended if you need to re-encode. +</p> +<a name="Concatenating-using-the-concat-demuxer"></a> +<h4 class="subsection">3.14.2 Concatenating using the concat <em>demuxer</em><span class="pull-right"><a class="anchor hidden-xs" href="#Concatenating-using-the-concat-demuxer" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-Concatenating-using-the-concat-demuxer" aria-hidden="true">TOC</a></span></h4> + +<p>FFmpeg has a <a href="ffmpeg-formats.html#concat"><code>concat</code></a> demuxer which you can use when you want to avoid a re-encode and +your format doesn’t support file level concatenation. +</p> +<a name="Concatenating-using-the-concat-protocol-_0028file-level_0029"></a> +<h4 class="subsection">3.14.3 Concatenating using the concat <em>protocol</em> (file level)<span class="pull-right"><a class="anchor hidden-xs" href="#Concatenating-using-the-concat-protocol-_0028file-level_0029" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-Concatenating-using-the-concat-protocol-_0028file-level_0029" aria-hidden="true">TOC</a></span></h4> + +<p>FFmpeg has a <a href="ffmpeg-protocols.html#concat"><code>concat</code></a> protocol designed specifically for that, with examples in the +documentation. +</p> +<p>A few multimedia containers (MPEG-1, MPEG-2 PS, DV) allow one to concatenate +video by merely concatenating the files containing them. +</p> +<p>Hence you may concatenate your multimedia files by first transcoding them to +these privileged formats, then using the humble <code>cat</code> command (or the +equally humble <code>copy</code> under Windows), and finally transcoding back to your +format of choice. +</p> +<div class="example"> +<pre class="example">ffmpeg -i input1.avi -qscale:v 1 intermediate1.mpg +ffmpeg -i input2.avi -qscale:v 1 intermediate2.mpg +cat intermediate1.mpg intermediate2.mpg > intermediate_all.mpg +ffmpeg -i intermediate_all.mpg -qscale:v 2 output.avi +</pre></div> + +<p>Additionally, you can use the <code>concat</code> protocol instead of <code>cat</code> or +<code>copy</code> which will avoid creation of a potentially huge intermediate file. +</p> +<div class="example"> +<pre class="example">ffmpeg -i input1.avi -qscale:v 1 intermediate1.mpg +ffmpeg -i input2.avi -qscale:v 1 intermediate2.mpg +ffmpeg -i concat:"intermediate1.mpg|intermediate2.mpg" -c copy intermediate_all.mpg +ffmpeg -i intermediate_all.mpg -qscale:v 2 output.avi +</pre></div> + +<p>Note that you may need to escape the character "|" which is special for many +shells. +</p> +<p>Another option is usage of named pipes, should your platform support it: +</p> +<div class="example"> +<pre class="example">mkfifo intermediate1.mpg +mkfifo intermediate2.mpg +ffmpeg -i input1.avi -qscale:v 1 -y intermediate1.mpg < /dev/null & +ffmpeg -i input2.avi -qscale:v 1 -y intermediate2.mpg < /dev/null & +cat intermediate1.mpg intermediate2.mpg |\ +ffmpeg -f mpeg -i - -c:v mpeg4 -c:a libmp3lame output.avi +</pre></div> + +<a name="Concatenating-using-raw-audio-and-video"></a> +<h4 class="subsection">3.14.4 Concatenating using raw audio and video<span class="pull-right"><a class="anchor hidden-xs" href="#Concatenating-using-raw-audio-and-video" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-Concatenating-using-raw-audio-and-video" aria-hidden="true">TOC</a></span></h4> + +<p>Similarly, the yuv4mpegpipe format, and the raw video, raw audio codecs also +allow concatenation, and the transcoding step is almost lossless. +When using multiple yuv4mpegpipe(s), the first line needs to be discarded +from all but the first stream. This can be accomplished by piping through +<code>tail</code> as seen below. Note that when piping through <code>tail</code> you +must use command grouping, <code>{ ;}</code>, to background properly. +</p> +<p>For example, let’s say we want to concatenate two FLV files into an +output.flv file: +</p> +<div class="example"> +<pre class="example">mkfifo temp1.a +mkfifo temp1.v +mkfifo temp2.a +mkfifo temp2.v +mkfifo all.a +mkfifo all.v +ffmpeg -i input1.flv -vn -f u16le -c:a pcm_s16le -ac 2 -ar 44100 - > temp1.a < /dev/null & +ffmpeg -i input2.flv -vn -f u16le -c:a pcm_s16le -ac 2 -ar 44100 - > temp2.a < /dev/null & +ffmpeg -i input1.flv -an -f yuv4mpegpipe - > temp1.v < /dev/null & +{ ffmpeg -i input2.flv -an -f yuv4mpegpipe - < /dev/null | tail -n +2 > temp2.v ; } & +cat temp1.a temp2.a > all.a & +cat temp1.v temp2.v > all.v & +ffmpeg -f u16le -c:a pcm_s16le -ac 2 -ar 44100 -i all.a \ + -f yuv4mpegpipe -i all.v \ + -y output.flv +rm temp[12].[av] all.[av] +</pre></div> + +<a name="Using-_002df-lavfi_002c-audio-becomes-mono-for-no-apparent-reason_002e"></a> +<h3 class="section">3.15 Using <samp>-f lavfi</samp>, audio becomes mono for no apparent reason.<span class="pull-right"><a class="anchor hidden-xs" href="#Using-_002df-lavfi_002c-audio-becomes-mono-for-no-apparent-reason_002e" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-Using-_002df-lavfi_002c-audio-becomes-mono-for-no-apparent-reason_002e" aria-hidden="true">TOC</a></span></h3> + +<p>Use <samp>-dumpgraph -</samp> to find out exactly where the channel layout is +lost. +</p> +<p>Most likely, it is through <code>auto-inserted aresample</code>. Try to understand +why the converting filter was needed at that place. +</p> +<p>Just before the output is a likely place, as <samp>-f lavfi</samp> currently +only support packed S16. +</p> +<p>Then insert the correct <code>aformat</code> explicitly in the filtergraph, +specifying the exact format. +</p> +<div class="example"> +<pre class="example">aformat=sample_fmts=s16:channel_layouts=stereo +</pre></div> + +<a name="Why-does-FFmpeg-not-see-the-subtitles-in-my-VOB-file_003f"></a> +<h3 class="section">3.16 Why does FFmpeg not see the subtitles in my VOB file?<span class="pull-right"><a class="anchor hidden-xs" href="#Why-does-FFmpeg-not-see-the-subtitles-in-my-VOB-file_003f" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-Why-does-FFmpeg-not-see-the-subtitles-in-my-VOB-file_003f" aria-hidden="true">TOC</a></span></h3> + +<p>VOB and a few other formats do not have a global header that describes +everything present in the file. Instead, applications are supposed to scan +the file to see what it contains. Since VOB files are frequently large, only +the beginning is scanned. If the subtitles happen only later in the file, +they will not be initially detected. +</p> +<p>Some applications, including the <code>ffmpeg</code> command-line tool, can only +work with streams that were detected during the initial scan; streams that +are detected later are ignored. +</p> +<p>The size of the initial scan is controlled by two options: <code>probesize</code> +(default ~5 Mo) and <code>analyzeduration</code> (default 5,000,000 µs = 5 s). For +the subtitle stream to be detected, both values must be large enough. +</p> +<a name="Why-was-the-ffmpeg-_002dsameq-option-removed_003f-What-to-use-instead_003f"></a> +<h3 class="section">3.17 Why was the <code>ffmpeg</code> <samp>-sameq</samp> option removed? What to use instead?<span class="pull-right"><a class="anchor hidden-xs" href="#Why-was-the-ffmpeg-_002dsameq-option-removed_003f-What-to-use-instead_003f" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-Why-was-the-ffmpeg-_002dsameq-option-removed_003f-What-to-use-instead_003f" aria-hidden="true">TOC</a></span></h3> + +<p>The <samp>-sameq</samp> option meant "same quantizer", and made sense only in a +very limited set of cases. Unfortunately, a lot of people mistook it for +"same quality" and used it in places where it did not make sense: it had +roughly the expected visible effect, but achieved it in a very inefficient +way. +</p> +<p>Each encoder has its own set of options to set the quality-vs-size balance, +use the options for the encoder you are using to set the quality level to a +point acceptable for your tastes. The most common options to do that are +<samp>-qscale</samp> and <samp>-qmax</samp>, but you should peruse the documentation +of the encoder you chose. +</p> +<a name="I-have-a-stretched-video_002c-why-does-scaling-does-not-fix-it_003f"></a> +<h3 class="section">3.18 I have a stretched video, why does scaling does not fix it?<span class="pull-right"><a class="anchor hidden-xs" href="#I-have-a-stretched-video_002c-why-does-scaling-does-not-fix-it_003f" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-I-have-a-stretched-video_002c-why-does-scaling-does-not-fix-it_003f" aria-hidden="true">TOC</a></span></h3> + +<p>A lot of video codecs and formats can store the <em>aspect ratio</em> of the +video: this is the ratio between the width and the height of either the full +image (DAR, display aspect ratio) or individual pixels (SAR, sample aspect +ratio). For example, EGA screens at resolution 640×350 had 4:3 DAR and 35:48 +SAR. +</p> +<p>Most still image processing work with square pixels, i.e. 1:1 SAR, but a lot +of video standards, especially from the analogic-numeric transition era, use +non-square pixels. +</p> +<p>Most processing filters in FFmpeg handle the aspect ratio to avoid +stretching the image: cropping adjusts the DAR to keep the SAR constant, +scaling adjusts the SAR to keep the DAR constant. +</p> +<p>If you want to stretch, or “unstretch”, the image, you need to override the +information with the +<a href="ffmpeg-filters.html#setdar_002c-setsar"><code>setdar or setsar filters</code></a>. +</p> +<p>Do not forget to examine carefully the original video to check whether the +stretching comes from the image or from the aspect ratio information. +</p> +<p>For example, to fix a badly encoded EGA capture, use the following commands, +either the first one to upscale to square pixels or the second one to set +the correct aspect ratio or the third one to avoid transcoding (may not work +depending on the format / codec / player / phase of the moon): +</p> +<div class="example"> +<pre class="example">ffmpeg -i ega_screen.nut -vf scale=640:480,setsar=1 ega_screen_scaled.nut +ffmpeg -i ega_screen.nut -vf setdar=4/3 ega_screen_anamorphic.nut +ffmpeg -i ega_screen.nut -aspect 4/3 -c copy ega_screen_overridden.nut +</pre></div> + +<span id="background-task"></span><a name="How-do-I-run-ffmpeg-as-a-background-task_003f"></a> +<h3 class="section">3.19 How do I run ffmpeg as a background task?<span class="pull-right"><a class="anchor hidden-xs" href="#How-do-I-run-ffmpeg-as-a-background-task_003f" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-How-do-I-run-ffmpeg-as-a-background-task_003f" aria-hidden="true">TOC</a></span></h3> + +<p>ffmpeg normally checks the console input, for entries like "q" to stop +and "?" to give help, while performing operations. ffmpeg does not have a way of +detecting when it is running as a background task. +When it checks the console input, that can cause the process running ffmpeg +in the background to suspend. +</p> +<p>To prevent those input checks, allowing ffmpeg to run as a background task, +use the <a href="ffmpeg.html#stdin-option"><code>-nostdin</code> option</a> +in the ffmpeg invocation. This is effective whether you run ffmpeg in a shell +or invoke ffmpeg in its own process via an operating system API. +</p> +<p>As an alternative, when you are running ffmpeg in a shell, you can redirect +standard input to <code>/dev/null</code> (on Linux and macOS) +or <code>NUL</code> (on Windows). You can do this redirect either +on the ffmpeg invocation, or from a shell script which calls ffmpeg. +</p> +<p>For example: +</p> +<div class="example"> +<pre class="example">ffmpeg -nostdin -i INPUT OUTPUT +</pre></div> + +<p>or (on Linux, macOS, and other UNIX-like shells): +</p> +<div class="example"> +<pre class="example">ffmpeg -i INPUT OUTPUT </dev/null +</pre></div> + +<p>or (on Windows): +</p> +<div class="example"> +<pre class="example">ffmpeg -i INPUT OUTPUT <NUL +</pre></div> + +<a name="How-do-I-prevent-ffmpeg-from-suspending-with-a-message-like-suspended-_0028tty-output_0029_003f"></a> +<h3 class="section">3.20 How do I prevent ffmpeg from suspending with a message like <em>suspended (tty output)</em>?<span class="pull-right"><a class="anchor hidden-xs" href="#How-do-I-prevent-ffmpeg-from-suspending-with-a-message-like-suspended-_0028tty-output_0029_003f" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-How-do-I-prevent-ffmpeg-from-suspending-with-a-message-like-suspended-_0028tty-output_0029_003f" aria-hidden="true">TOC</a></span></h3> + +<p>If you run ffmpeg in the background, you may find that its process suspends. +There may be a message like <em>suspended (tty output)</em>. The question is how +to prevent the process from being suspended. +</p> +<p>For example: +</p> +<div class="example"> +<pre class="example">% ffmpeg -i INPUT OUTPUT &> ~/tmp/log.txt & +[1] 93352 +% +[1] + suspended (tty output) ffmpeg -i INPUT OUTPUT &> +</pre></div> + +<p>The message "tty output" notwithstanding, the problem here is that +ffmpeg normally checks the console input when it runs. The operating system +detects this, and suspends the process until you can bring it to the +foreground and attend to it. +</p> +<p>The solution is to use the right techniques to tell ffmpeg not to consult +console input. You can use the +<a href="ffmpeg.html#stdin-option"><code>-nostdin</code> option</a>, +or redirect standard input with <code>< /dev/null</code>. +See FAQ +<a href="#background-task"><em>How do I run ffmpeg as a background task?</em></a> +for details. +</p> +<a name="Development"></a> +<h2 class="chapter">4 Development<span class="pull-right"><a class="anchor hidden-xs" href="#Development" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-Development" aria-hidden="true">TOC</a></span></h2> + +<a name="Are-there-examples-illustrating-how-to-use-the-FFmpeg-libraries_002c-particularly-libavcodec-and-libavformat_003f"></a> +<h3 class="section">4.1 Are there examples illustrating how to use the FFmpeg libraries, particularly libavcodec and libavformat?<span class="pull-right"><a class="anchor hidden-xs" href="#Are-there-examples-illustrating-how-to-use-the-FFmpeg-libraries_002c-particularly-libavcodec-and-libavformat_003f" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-Are-there-examples-illustrating-how-to-use-the-FFmpeg-libraries_002c-particularly-libavcodec-and-libavformat_003f" aria-hidden="true">TOC</a></span></h3> + +<p>Yes. Check the <samp>doc/examples</samp> directory in the source +repository, also available online at: +<a href="https://github.com/FFmpeg/FFmpeg/tree/master/doc/examples">https://github.com/FFmpeg/FFmpeg/tree/master/doc/examples</a>. +</p> +<p>Examples are also installed by default, usually in +<code>$PREFIX/share/ffmpeg/examples</code>. +</p> +<p>Also you may read the Developers Guide of the FFmpeg documentation. Alternatively, +examine the source code for one of the many open source projects that +already incorporate FFmpeg at (<a href="projects.html">projects.html</a>). +</p> +<a name="Can-you-support-my-C-compiler-XXX_003f"></a> +<h3 class="section">4.2 Can you support my C compiler XXX?<span class="pull-right"><a class="anchor hidden-xs" href="#Can-you-support-my-C-compiler-XXX_003f" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-Can-you-support-my-C-compiler-XXX_003f" aria-hidden="true">TOC</a></span></h3> + +<p>It depends. If your compiler is C99-compliant, then patches to support +it are likely to be welcome if they do not pollute the source code +with <code>#ifdef</code>s related to the compiler. +</p> +<a name="Is-Microsoft-Visual-C_002b_002b-supported_003f"></a> +<h3 class="section">4.3 Is Microsoft Visual C++ supported?<span class="pull-right"><a class="anchor hidden-xs" href="#Is-Microsoft-Visual-C_002b_002b-supported_003f" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-Is-Microsoft-Visual-C_002b_002b-supported_003f" aria-hidden="true">TOC</a></span></h3> + +<p>Yes. Please see the <a href="platform.html">Microsoft Visual C++</a> +section in the FFmpeg documentation. +</p> +<a name="Can-you-add-automake_002c-libtool-or-autoconf-support_003f"></a> +<h3 class="section">4.4 Can you add automake, libtool or autoconf support?<span class="pull-right"><a class="anchor hidden-xs" href="#Can-you-add-automake_002c-libtool-or-autoconf-support_003f" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-Can-you-add-automake_002c-libtool-or-autoconf-support_003f" aria-hidden="true">TOC</a></span></h3> + +<p>No. These tools are too bloated and they complicate the build. +</p> +<a name="Why-not-rewrite-FFmpeg-in-object_002doriented-C_002b_002b_003f"></a> +<h3 class="section">4.5 Why not rewrite FFmpeg in object-oriented C++?<span class="pull-right"><a class="anchor hidden-xs" href="#Why-not-rewrite-FFmpeg-in-object_002doriented-C_002b_002b_003f" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-Why-not-rewrite-FFmpeg-in-object_002doriented-C_002b_002b_003f" aria-hidden="true">TOC</a></span></h3> + +<p>FFmpeg is already organized in a highly modular manner and does not need to +be rewritten in a formal object language. Further, many of the developers +favor straight C; it works for them. For more arguments on this matter, +read <a href="https://web.archive.org/web/20111004021423/http://kernel.org/pub/linux/docs/lkml/#s15">"Programming Religion"</a>. +</p> +<a name="Why-are-the-ffmpeg-programs-devoid-of-debugging-symbols_003f"></a> +<h3 class="section">4.6 Why are the ffmpeg programs devoid of debugging symbols?<span class="pull-right"><a class="anchor hidden-xs" href="#Why-are-the-ffmpeg-programs-devoid-of-debugging-symbols_003f" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-Why-are-the-ffmpeg-programs-devoid-of-debugging-symbols_003f" aria-hidden="true">TOC</a></span></h3> + +<p>The build process creates <code>ffmpeg_g</code>, <code>ffplay_g</code>, etc. which +contain full debug information. Those binaries are stripped to create +<code>ffmpeg</code>, <code>ffplay</code>, etc. If you need the debug information, use +the *_g versions. +</p> +<a name="I-do-not-like-the-LGPL_002c-can-I-contribute-code-under-the-GPL-instead_003f"></a> +<h3 class="section">4.7 I do not like the LGPL, can I contribute code under the GPL instead?<span class="pull-right"><a class="anchor hidden-xs" href="#I-do-not-like-the-LGPL_002c-can-I-contribute-code-under-the-GPL-instead_003f" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-I-do-not-like-the-LGPL_002c-can-I-contribute-code-under-the-GPL-instead_003f" aria-hidden="true">TOC</a></span></h3> + +<p>Yes, as long as the code is optional and can easily and cleanly be placed +under #if CONFIG_GPL without breaking anything. So, for example, a new codec +or filter would be OK under GPL while a bug fix to LGPL code would not. +</p> +<a name="I_0027m-using-FFmpeg-from-within-my-C-application-but-the-linker-complains-about-missing-symbols-from-the-libraries-themselves_002e"></a> +<h3 class="section">4.8 I’m using FFmpeg from within my C application but the linker complains about missing symbols from the libraries themselves.<span class="pull-right"><a class="anchor hidden-xs" href="#I_0027m-using-FFmpeg-from-within-my-C-application-but-the-linker-complains-about-missing-symbols-from-the-libraries-themselves_002e" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-I_0027m-using-FFmpeg-from-within-my-C-application-but-the-linker-complains-about-missing-symbols-from-the-libraries-themselves_002e" aria-hidden="true">TOC</a></span></h3> + +<p>FFmpeg builds static libraries by default. In static libraries, dependencies +are not handled. That has two consequences. First, you must specify the +libraries in dependency order: <code>-lavdevice</code> must come before +<code>-lavformat</code>, <code>-lavutil</code> must come after everything else, etc. +Second, external libraries that are used in FFmpeg have to be specified too. +</p> +<p>An easy way to get the full list of required libraries in dependency order +is to use <code>pkg-config</code>. +</p> +<div class="example"> +<pre class="example">c99 -o program program.c $(pkg-config --cflags --libs libavformat libavcodec) +</pre></div> + +<p>See <samp>doc/example/Makefile</samp> and <samp>doc/example/pc-uninstalled</samp> for +more details. +</p> +<a name="I_0027m-using-FFmpeg-from-within-my-C_002b_002b-application-but-the-linker-complains-about-missing-symbols-which-seem-to-be-available_002e"></a> +<h3 class="section">4.9 I’m using FFmpeg from within my C++ application but the linker complains about missing symbols which seem to be available.<span class="pull-right"><a class="anchor hidden-xs" href="#I_0027m-using-FFmpeg-from-within-my-C_002b_002b-application-but-the-linker-complains-about-missing-symbols-which-seem-to-be-available_002e" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-I_0027m-using-FFmpeg-from-within-my-C_002b_002b-application-but-the-linker-complains-about-missing-symbols-which-seem-to-be-available_002e" aria-hidden="true">TOC</a></span></h3> + +<p>FFmpeg is a pure C project, so to use the libraries within your C++ application +you need to explicitly state that you are using a C library. You can do this by +encompassing your FFmpeg includes using <code>extern "C"</code>. +</p> +<p>See <a href="http://www.parashift.com/c++-faq-lite/mixing-c-and-cpp.html#faq-32.3">http://www.parashift.com/c++-faq-lite/mixing-c-and-cpp.html#faq-32.3</a> +</p> +<a name="I_0027m-using-libavutil-from-within-my-C_002b_002b-application-but-the-compiler-complains-about-_0027UINT64_005fC_0027-was-not-declared-in-this-scope"></a> +<h3 class="section">4.10 I’m using libavutil from within my C++ application but the compiler complains about ’UINT64_C’ was not declared in this scope<span class="pull-right"><a class="anchor hidden-xs" href="#I_0027m-using-libavutil-from-within-my-C_002b_002b-application-but-the-compiler-complains-about-_0027UINT64_005fC_0027-was-not-declared-in-this-scope" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-I_0027m-using-libavutil-from-within-my-C_002b_002b-application-but-the-compiler-complains-about-_0027UINT64_005fC_0027-was-not-declared-in-this-scope" aria-hidden="true">TOC</a></span></h3> + +<p>FFmpeg is a pure C project using C99 math features, in order to enable C++ +to use them you have to append -D__STDC_CONSTANT_MACROS to your CXXFLAGS +</p> +<a name="I-have-a-file-in-memory-_002f-a-API-different-from-_002aopen_002f_002aread_002f-libc-how-do-I-use-it-with-libavformat_003f"></a> +<h3 class="section">4.11 I have a file in memory / a API different from *open/*read/ libc how do I use it with libavformat?<span class="pull-right"><a class="anchor hidden-xs" href="#I-have-a-file-in-memory-_002f-a-API-different-from-_002aopen_002f_002aread_002f-libc-how-do-I-use-it-with-libavformat_003f" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-I-have-a-file-in-memory-_002f-a-API-different-from-_002aopen_002f_002aread_002f-libc-how-do-I-use-it-with-libavformat_003f" aria-hidden="true">TOC</a></span></h3> + +<p>You have to create a custom AVIOContext using <code>avio_alloc_context</code>, +see <samp>libavformat/aviobuf.c</samp> in FFmpeg and <samp>libmpdemux/demux_lavf.c</samp> in MPlayer or MPlayer2 sources. +</p> +<a name="Where-is-the-documentation-about-ffv1_002c-msmpeg4_002c-asv1_002c-4xm_003f"></a> +<h3 class="section">4.12 Where is the documentation about ffv1, msmpeg4, asv1, 4xm?<span class="pull-right"><a class="anchor hidden-xs" href="#Where-is-the-documentation-about-ffv1_002c-msmpeg4_002c-asv1_002c-4xm_003f" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-Where-is-the-documentation-about-ffv1_002c-msmpeg4_002c-asv1_002c-4xm_003f" aria-hidden="true">TOC</a></span></h3> + +<p>see <a href="https://www.ffmpeg.org/~michael/">https://www.ffmpeg.org/~michael/</a> +</p> +<a name="How-do-I-feed-H_002e263_002dRTP-_0028and-other-codecs-in-RTP_0029-to-libavcodec_003f"></a> +<h3 class="section">4.13 How do I feed H.263-RTP (and other codecs in RTP) to libavcodec?<span class="pull-right"><a class="anchor hidden-xs" href="#How-do-I-feed-H_002e263_002dRTP-_0028and-other-codecs-in-RTP_0029-to-libavcodec_003f" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-How-do-I-feed-H_002e263_002dRTP-_0028and-other-codecs-in-RTP_0029-to-libavcodec_003f" aria-hidden="true">TOC</a></span></h3> + +<p>Even if peculiar since it is network oriented, RTP is a container like any +other. You have to <em>demux</em> RTP before feeding the payload to libavcodec. +In this specific case please look at RFC 4629 to see how it should be done. +</p> +<a name="AVStream_002er_005fframe_005frate-is-wrong_002c-it-is-much-larger-than-the-frame-rate_002e"></a> +<h3 class="section">4.14 AVStream.r_frame_rate is wrong, it is much larger than the frame rate.<span class="pull-right"><a class="anchor hidden-xs" href="#AVStream_002er_005fframe_005frate-is-wrong_002c-it-is-much-larger-than-the-frame-rate_002e" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-AVStream_002er_005fframe_005frate-is-wrong_002c-it-is-much-larger-than-the-frame-rate_002e" aria-hidden="true">TOC</a></span></h3> + +<p><code>r_frame_rate</code> is NOT the average frame rate, it is the smallest frame rate +that can accurately represent all timestamps. So no, it is not +wrong if it is larger than the average! +For example, if you have mixed 25 and 30 fps content, then <code>r_frame_rate</code> +will be 150 (it is the least common multiple). +If you are looking for the average frame rate, see <code>AVStream.avg_frame_rate</code>. +</p> +<a name="Why-is-make-fate-not-running-all-tests_003f"></a> +<h3 class="section">4.15 Why is <code>make fate</code> not running all tests?<span class="pull-right"><a class="anchor hidden-xs" href="#Why-is-make-fate-not-running-all-tests_003f" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-Why-is-make-fate-not-running-all-tests_003f" aria-hidden="true">TOC</a></span></h3> + +<p>Make sure you have the fate-suite samples and the <code>SAMPLES</code> Make variable +or <code>FATE_SAMPLES</code> environment variable or the <code>--samples</code> +<code>configure</code> option is set to the right path. +</p> +<a name="Why-is-make-fate-not-finding-the-samples_003f"></a> +<h3 class="section">4.16 Why is <code>make fate</code> not finding the samples?<span class="pull-right"><a class="anchor hidden-xs" href="#Why-is-make-fate-not-finding-the-samples_003f" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-Why-is-make-fate-not-finding-the-samples_003f" aria-hidden="true">TOC</a></span></h3> + +<p>Do you happen to have a <code>~</code> character in the samples path to indicate a +home directory? The value is used in ways where the shell cannot expand it, +causing FATE to not find files. Just replace <code>~</code> by the full path. +</p> + <p style="font-size: small;"> + This document was generated using <a href="https://www.gnu.org/software/texinfo/"><em>makeinfo</em></a>. + </p> + </div> + </body> +</html> |