[FFmpeg-user] Getting wrong timestamps with my decoding code, but showinfo filter shows correct timestamps

[Andreas Sommer]

The following problem happens only with MOV files (.3g2 extension) that
were encoded after the following change was introduced in movenc.c (commit
b02493e476):

            while(track->timescale < 10000)
                track->timescale *= 2;

With my own decoding source code that uses libavformat:

    bytesDecoded = avcodec_decode_video2(m_videoCodecContext,
m_currentFrame, &frameFinished, &packet);
    [...]
    if (frameFinished)
    {
        int64_t  best_effort_timestamp=
av_frame_get_best_effort_timestamp(m_currentFrame);
        pts =best_effort_timestamp * (float)
av_q2d(m_videoCodecContext->time_base);

        printf("pts %f, %f, %f (fps=%f)\n", pts, (float) packet.dts,
av_q2d(m_videoCodecContext->time_base), (float) packet.dts / pts);
        [...]

..., I always get these values for the first frame:

pts 25.600000, 512.000000, 0.050000 (fps=20.000000)

so the first frame is at 25.6 seconds which is wrong. However if I use
ffmpeg.exe from the same build, and test that video file with "ffmpeg.exe
-i thatfile.3g2 -vf showinfo -an -y dummy.3g2 >log.txt 2>&1", I'm getting
this info:

[Parsed_showinfo_0 @ 00CA0B20] n:0 pts:476 pts_time:0.0464844 rawpts:476
timebase:0.000098 pos:67 fmt:yuv420p sar:12/11 s:176x144 i:P iskey:1 type:I
checksum:EB50BAC2 plane_checksum:[D057F94B 29FD60B4 29FD60B4]

Here the first frame is at roughly 0.05 seconds which is correct (don't
know why pts=476 instead of 512, possibly audio sync or whatever, probably
doesn't matter here). And look at the timebase here which is 0.000098 as
compared to 0.05 with my source code. What am I doing wrong? Do I have to
change the calculations for the pts variable to get the timestamp in
seconds?

Thanks a bunch
Andreas