wrong duration output with -t on audio with edit lists (preroll)

[Cosmin Stejerean]

Given a typical AAC audio file in MP4 format it will contain an edit list for the necessary preroll duration. Attempting to decode a subset of such a file (with -t) will result in wrong duration output. Reproduced this in ffmpeg 5

Steps to reproduce

1. Acquire a test AAC in MP4 file, or trivially create one as follows

ffmpeg -f lavfi -t 30 -i anullsrc=channel_layout=stereo:sample_rate=48000 -codec:a libfdk_aac -profile:a aac_he test.mp4

2. Attempt to decode the first 10s of audio from this file

ffmpeg -i test.mp4 -t 10 out.wav

3. Observe that the output is not in fact 10s long, it is missing precisely the duration of the start edit list in the original

ffprobe out.wav

Duration: 00:00:09.90, bitrate: 1536 kb/s

4. Using -t as a demuxer option (before -i) results in correct output

ffmpeg -t 10 -i test.mp4  out2.wav
ffprobe out2.wav

Duration: 00:00:10.00, bitrate: 1536 kb/s

Based on this I believe that most likely the -t option is wrongly considering time without the edit list offset at the beginning, at least on the audio case. I have not verified what happens with -t on video inputs that also contain edit lists.

[James]

Should be fixed in 5114ce1e2a4c71ddf4971ad3cf9bd43ae16571c3

[Balling]

It really is an issue we faced (samples are indeed HE-AACv2) ​https://bugs.chromium.org/p/chromium/issues/detail?id=1234227

Thanks for fixing this!