[Libav-user] Different decoded frame number from ffmpeg commend line and the example demuxing

[Sergey Fedorov]

‘-r[:stream_specifier] fps (input/output,per-stream)’

Set frame rate (Hz value, fraction or abbreviation).

As an input option, ignore any timestamps stored in the file and
instead generate timestamps assuming constant frame rate fps.

As an output option, duplicate or drop input frames to achieve
constant output frame rate fps.


2013/7/23 Liang Zhang <liazhang2000 at gmail.com>:
> Hello,
>
> I'm learning how to use libav to decode the video data into YUV. I try to
> use ffmpeg commend line and also use the example program "demuxing" which is
> provided in ffmpeg documentation. It surprised me that both resulted in
> different frame number.
>
> I use the following ffmpeg commend line
>
> ffmpeg -y -i sample.mp4 -an -r 24 -pix_fmt rgb24 -vcodec tiff tif/%06d.tif
>
> to decode one video data file and get, e.g., 1460 frames.
>
> Then, I used the example program "demuxing"
>
> demuxing  sample.mp4  out_video out_audio
>
> to decode the same file and I got 1821 frames.
>
> Can someone help me explain why the frame number is different with these two
> methods?
>
> FYI, I run the program in Ubuntu operating system.
>
> Thanks,
>
>
>
> liang
>
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