[Ffmpeg-devel] PTS calculation revisited (original) (raw)

Colin Ward lists
Sun Feb 19 12:49:50 CET 2006

Hi all.

I have a PTS calculation system in place whereby it seems to work well for most file formats. It is based on scanning through various example code such as ffplay.c. However, for some files the results are incorrect. Take a look at:

http://www.codehq.org/NewMouse.wmv

The output from my media player when playing this is as follows:

AMC Info: CFFMPEG::Open() => File recognised as asf AMC Info: CFFMPEG::Open() => Audio: wmav2, 32000 Hz, stereo, 32 kb/s AMC Info: CFFMPEG::Open() => Video: wmv2, yuv420p, 320x240 Input #0, asf, from 'Lah': Duration: 00:00:16.4, start: 3.100000, bitrate: 355 kb/s Stream #0.0: Audio: wmav2, 32000 Hz, stereo, 32 kb/s Stream #0.1, 30.00 fps(r): Video: wmv2, yuv420p, 320x240

As you can see it is wmv2 video and is 30 FPS. When I allocate a video frame and decode it with avcodec_decode_video() the AVFrame->pts value that is returned is always zero. So I manually calculate the delta between frames by using the following code:

double frame_delay = av_q2d(format_context->streams[video_stream]->codec->time_base); frame_delay *= 1000; // Convert to milliseconds

However, this always results in frame_delay being 1 (millisecond!) rather than 33.3333 which it should be in order to be played at 30 FPS.

What am I doing wrong?

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