frame index of video frame

[mkassner]

Since frame.pts is often only by coincidence equal to frame index in video stream (and will ultimately fail with non constant frame rates), I was hoping for frame.index to represent the frame index in the steam.

However, it appears that frame index == encoded frame count on frame creation. This mean that after a seek the index become -at least the way I understand it- false.

Any ideas on how to fix that?

[mikeboers]

Unfortunately, I don't think that sort of information is available from FFmpeg/Libav, as it may not be a common thing for codecs to encode into individual frames/packets.

[mkassner]

ok, that makes sense. I just thought it might be possible because of a few members in the AVframe struct:

int     coded_picture_number
    #picture number in bitstream order 

int     display_picture_number
    #picture number in display order 

[mikeboers]

They look promising, but (IIRC) they are set in essentially the same manner as PyAV's Frame.index, and just won't work across a seek. =[

On Jul 12, 2014, at 1:17 AM, mkassner notifications@github.com wrote:

ok, that makes sense. I just thought it might be possible because of a few members in the AVframe struct:

int coded_picture_number
#picture number in bitstream order

int display_picture_number
#picture number in display order
—
Reply to this email directly or view it on GitHub.

[mkassner]

Alright. Thanks for the clarification!

[mikeboers]

Seems like the documentation should be improved, at the least.

[markreidvfx]

If the video is constant frame rate, the frame number should be pts_seconds / frame_rate. That might be good enough for most codecs, assuming the file is encoded correctly, doesn't drop or repeat frames. The only way to do it 100% accurately as far as I understand is to decode every frame and count and then make a pts seek table.
That's what this project does, https://github.com/lbrandy/ffmpeg-fas

[mkassner]

I was hoping for frame indices of variable frame rate videos, otherwise frame index is always just pts/framerate like you said. I was hoping seek tables to already be present in the container. Building one ourselves is not hard so I will go with that!

[mikeboers]

I'm going to leave this open as a documentation issue.

[funkybob]

In my own code, after much painful and tedious research :) I have the following:

'''
        PTS (Presentation Time Stamp), which indicates when this frame should
        be shown, is expressed according to stream.time_base.

        We can compare the PTS to frame numbers if we scale by:
            (stream.average_rate / stream.time_base)
'''
pts_scale = video_stream.average_rate * video_stream.time_base

frame_pts = int(frame_index / pts_scale)

I'm not certain how portable this is, as we only use MP4 video streams.

[jlaine]

I'm going to close this issue, as the following time-related attributes are properly documented nowadays:

• dts
• pts
• time_base