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lavf: add av_guess_frame_sample_aspect_ratio function

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Guesses the sample aspect ratio of a frame, based on both the stream and the
frame aspect ratio.

Since the frame aspect ratio is set by the codec but the stream aspect ratio
is set by the demuxer, these two may not be equal. This function tries to
return the value that you should use if you would like to display the frame.

Basic logic is to use the stream aspect ratio if it is set to something sane
otherwise use the frame aspect ratio. This way a container setting, which is
usually easy to modify can override the coded value in the frames.

Signed-off-by: Marton Balint <cus@passwd.hu>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
This commit is contained in:
Marton Balint
2012-05-07 20:27:08 +02:00
committed by Michael Niedermayer
parent 9cf5bcded0
commit 94a9ac1277
4 changed files with 46 additions and 1 deletions
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22
libavformat/utils.c
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@ -4414,3 +4414,25 @@ const struct AVCodecTag *avformat_get_riff_audio_tags(void)
{
return ff_codec_wav_tags;
}
AVRational av_guess_sample_aspect_ratio(AVFormatContext *format, AVStream *stream, AVFrame *frame)
{
AVRational undef = {0, 1};
AVRational stream_sample_aspect_ratio = stream ? stream->sample_aspect_ratio : undef;
AVRational frame_sample_aspect_ratio = frame ? frame->sample_aspect_ratio : undef;
av_reduce(&stream_sample_aspect_ratio.num, &stream_sample_aspect_ratio.den,
stream_sample_aspect_ratio.num, stream_sample_aspect_ratio.den, INT_MAX);
if (stream_sample_aspect_ratio.num <= 0 || stream_sample_aspect_ratio.den <= 0)
stream_sample_aspect_ratio = undef;
av_reduce(&frame_sample_aspect_ratio.num, &frame_sample_aspect_ratio.den,
frame_sample_aspect_ratio.num, frame_sample_aspect_ratio.den, INT_MAX);
if (frame_sample_aspect_ratio.num <= 0 || frame_sample_aspect_ratio.den <= 0)
frame_sample_aspect_ratio = undef;
if (stream_sample_aspect_ratio.num)
return stream_sample_aspect_ratio;
else
return frame_sample_aspect_ratio;
}