mirror of https://git.ffmpeg.org/ffmpeg.git
Merge remote-tracking branch 'cigaes/master'
* cigaes/master: doc/faq: explain DAR/SAR preserving. doc: set documentencoding on toplevel texi files. Merged-by: Michael Niedermayer <michaelni@gmx.at>
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\input texinfo @c -*- texinfo -*-
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\input texinfo @c -*- texinfo -*-
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@documentencoding UTF-8
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@settitle Developer Documentation
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@settitle Developer Documentation
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@titlepage
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@titlepage
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35
doc/faq.texi
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doc/faq.texi
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\input texinfo @c -*- texinfo -*-
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\input texinfo @c -*- texinfo -*-
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@documentencoding UTF-8
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@settitle FFmpeg FAQ
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@settitle FFmpeg FAQ
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@titlepage
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@titlepage
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@ -466,6 +467,40 @@ point acceptable for your tastes. The most common options to do that are
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@option{-qscale} and @option{-qmax}, but you should peruse the documentation
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@option{-qscale} and @option{-qmax}, but you should peruse the documentation
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of the encoder you chose.
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of the encoder you chose.
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@section I have a stretched video, why does scaling does not fix it?
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A lot of video codecs and formats can store the @emph{aspect ratio} of the
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video: this is the ratio between the width and the height of either the full
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image (DAR, display aspect ratio) or individual pixels (SAR, sample aspect
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ratio). For example, EGA screens at resolution 640×350 had 4:3 DAR and 35:48
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SAR.
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Most still image processing work with square pixels, i.e. 1:1 SAR, but a lot
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of video standards, especially from the analogic-numeric transition era, use
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non-square pixels.
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Most processing filters in FFmpeg handle the aspect ratio to avoid
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stretching the image: cropping adjusts the DAR to keep the SAR constant,
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scaling adjusts the SAR to keep the DAR constant.
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If you want to stretch, or “unstretch”, the image, you need to override the
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information with the
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@url{http://ffmpeg.org/ffmpeg-filters.html#setdar_002c-setsar, @code{setdar or setsar filters}}.
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Do not forget to examine carefully the original video to check whether the
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stretching comes from the image or from the aspect ratio information.
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For example, to fix a badly encoded EGA capture, use the following commands,
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either the first one to upscale to square pixels or the second one to set
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the correct aspect ratio or the third one to avoid transcoding (may not work
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depending on the format / codec / player / phase of the moon):
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@example
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ffmpeg -i ega_screen.nut -vf scale=640:480,setsar=1 ega_screen_scaled.nut
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ffmpeg -i ega_screen.nut -vf setdar=4/3 ega_screen_anamorphic.nut
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ffmpeg -i ega_screen.nut -aspect 4/3 -c copy ega_screen_overridden.nut
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@end example
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@chapter Development
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@chapter Development
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@section Are there examples illustrating how to use the FFmpeg libraries, particularly libavcodec and libavformat?
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@section Are there examples illustrating how to use the FFmpeg libraries, particularly libavcodec and libavformat?
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\input texinfo @c -*- texinfo -*-
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\input texinfo @c -*- texinfo -*-
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@documentencoding UTF-8
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@settitle FFmpeg Automated Testing Environment
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@settitle FFmpeg Automated Testing Environment
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@titlepage
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@titlepage
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\input texinfo @c -*- texinfo -*-
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\input texinfo @c -*- texinfo -*-
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@documentencoding UTF-8
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@settitle FFmpeg Bitstream Filters Documentation
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@settitle FFmpeg Bitstream Filters Documentation
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@titlepage
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@titlepage
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\input texinfo @c -*- texinfo -*-
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\input texinfo @c -*- texinfo -*-
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@documentencoding UTF-8
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@settitle FFmpeg Codecs Documentation
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@settitle FFmpeg Codecs Documentation
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@titlepage
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@titlepage
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\input texinfo @c -*- texinfo -*-
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\input texinfo @c -*- texinfo -*-
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@documentencoding UTF-8
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@settitle FFmpeg Devices Documentation
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@settitle FFmpeg Devices Documentation
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@titlepage
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@titlepage
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\input texinfo @c -*- texinfo -*-
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\input texinfo @c -*- texinfo -*-
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@documentencoding UTF-8
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@settitle FFmpeg Filters Documentation
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@settitle FFmpeg Filters Documentation
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@titlepage
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@titlepage
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\input texinfo @c -*- texinfo -*-
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\input texinfo @c -*- texinfo -*-
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@documentencoding UTF-8
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@settitle FFmpeg Formats Documentation
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@settitle FFmpeg Formats Documentation
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@titlepage
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@titlepage
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\input texinfo @c -*- texinfo -*-
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\input texinfo @c -*- texinfo -*-
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@documentencoding UTF-8
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@settitle FFmpeg Protocols Documentation
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@settitle FFmpeg Protocols Documentation
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@titlepage
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@titlepage
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\input texinfo @c -*- texinfo -*-
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\input texinfo @c -*- texinfo -*-
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@documentencoding UTF-8
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@settitle FFmpeg Resampler Documentation
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@settitle FFmpeg Resampler Documentation
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@titlepage
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@titlepage
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\input texinfo @c -*- texinfo -*-
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\input texinfo @c -*- texinfo -*-
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@documentencoding UTF-8
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@settitle FFmpeg Scaler Documentation
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@settitle FFmpeg Scaler Documentation
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@titlepage
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@titlepage
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\input texinfo @c -*- texinfo -*-
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\input texinfo @c -*- texinfo -*-
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@documentencoding UTF-8
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@settitle FFmpeg Utilities Documentation
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@settitle FFmpeg Utilities Documentation
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@titlepage
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@titlepage
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\input texinfo @c -*- texinfo -*-
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\input texinfo @c -*- texinfo -*-
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@documentencoding UTF-8
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@settitle ffmpeg Documentation
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@settitle ffmpeg Documentation
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@titlepage
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@titlepage
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\input texinfo @c -*- texinfo -*-
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\input texinfo @c -*- texinfo -*-
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@documentencoding UTF-8
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@settitle ffplay Documentation
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@settitle ffplay Documentation
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@titlepage
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@titlepage
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\input texinfo @c -*- texinfo -*-
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\input texinfo @c -*- texinfo -*-
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@documentencoding UTF-8
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@settitle ffprobe Documentation
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@settitle ffprobe Documentation
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@titlepage
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@titlepage
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\input texinfo @c -*- texinfo -*-
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\input texinfo @c -*- texinfo -*-
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@documentencoding UTF-8
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@settitle ffserver Documentation
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@settitle ffserver Documentation
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@titlepage
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@titlepage
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\input texinfo @c -*- texinfo -*-
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\input texinfo @c -*- texinfo -*-
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@documentencoding UTF-8
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@settitle General Documentation
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@settitle General Documentation
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@titlepage
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@titlepage
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\input texinfo @c -*- texinfo -*-
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\input texinfo @c -*- texinfo -*-
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@documentencoding UTF-8
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@settitle Using git to develop FFmpeg
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@settitle Using git to develop FFmpeg
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\input texinfo @c -*- texinfo -*-
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\input texinfo @c -*- texinfo -*-
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@documentencoding UTF-8
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@settitle Libavcodec Documentation
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@settitle Libavcodec Documentation
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@titlepage
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@titlepage
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\input texinfo @c -*- texinfo -*-
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@documentencoding UTF-8
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@settitle Libavdevice Documentation
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@settitle Libavdevice Documentation
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@titlepage
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@titlepage
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\input texinfo @c -*- texinfo -*-
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\input texinfo @c -*- texinfo -*-
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@documentencoding UTF-8
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@settitle Libavfilter Documentation
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@settitle Libavfilter Documentation
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@titlepage
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@titlepage
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\input texinfo @c -*- texinfo -*-
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\input texinfo @c -*- texinfo -*-
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@documentencoding UTF-8
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@settitle Libavformat Documentation
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@settitle Libavformat Documentation
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@titlepage
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@titlepage
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\input texinfo @c -*- texinfo -*-
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\input texinfo @c -*- texinfo -*-
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@documentencoding UTF-8
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@settitle Libavutil Documentation
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@settitle Libavutil Documentation
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@titlepage
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@titlepage
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\input texinfo @c -*- texinfo -*-
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\input texinfo @c -*- texinfo -*-
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@documentencoding UTF-8
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@settitle Libswresample Documentation
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@settitle Libswresample Documentation
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@titlepage
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\input texinfo @c -*- texinfo -*-
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\input texinfo @c -*- texinfo -*-
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@documentencoding UTF-8
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@settitle Libswscale Documentation
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@settitle Libswscale Documentation
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@titlepage
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\input texinfo @c -*- texinfo -*-
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\input texinfo @c -*- texinfo -*-
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@documentencoding UTF-8
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@settitle NUT
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@settitle NUT
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\input texinfo @c -*- texinfo -*-
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\input texinfo @c -*- texinfo -*-
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@documentencoding UTF-8
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@settitle Platform Specific Information
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@settitle Platform Specific Information
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@titlepage
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@titlepage
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