[FFmpeg-devel] Interpretation of duration field in AVI super index chunk

Tobias Rapp t.rapp at noa-audio.com
Tue Feb 24 16:33:10 CET 2015


I am currently trying to interpret the index data of HuffYuv/PCM AVI 
files written by FFmpeg. If the file is larger than 2GiB an "AVIX" RIFF 
chunk is added for each 2GiB-block, each of these blocks gets an OpenDML 
chunk index "ix00" and an OpenDML super index chunk "indx" is written 
for each stream that contains the file offset of the according chunk 
indexes together with its size and total duration.

For this super index "duration" entry the documentation I have found 
states that it shall be the "time span in stream ticks" [1]. FFmpeg 
seems to write the chunk count instead which is correct for video 
streams where one data chunk "00dc" corresponds to one frame. For audio 
streams one data chunk "01wb" usually contains multiple samples.

I guess for audio streams the "duration" should be multiplied by the 
samples-per-chunk factor in avienc.c to allow third-party applications 
to jump to the correct AVIX RIFF segment based on a given timestamp.

Any comments?


[1] http://www.the-labs.com/Video/odmlff2-avidef.pdf

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