audio_frame_queue: Incorrect dequeued timestamps

[Lastique]

The ff_af_queue_add/ff_af_queue_remove functions do not reproduce the timestamps that the user provides in AVFrame::pts. Effectively, the af_queue introduces a negative offset in the timestamps produced in AVPacket::pts.

For example, aacenc encoder has a delay of 1024 samples. If the user provides AVFrame::pts = 0 in the first frame sent to the encoder then the first packet received from the encoder will have AVPacket::pts = -1024.

Encoders should produce encoded timestamps equivalent to the timestamps that were passed by the users in decoded frames.

This problem was found when using ffmpeg through C API, I'm not sure it can be shown from CLI.

[Carl Eugen Hoyos]

Is the issue reproducible with current FFmpeg git head?
Please provide a simplified testcase that allows to reproduce.

[Lastique]

A test case that demonstrates the problem

[Lastique]

I've attached a test case that demonstrates the problem. The test output is:

Input pts: 0, output pts: -2048
Input pts: 1024, output pts: -1024
Input pts: 2048, output pts: 0
Input pts: 3072, output pts: 1024
Input pts: 4096, output pts: 2048

The expected output should list the same values for input and output timestamps.

[mkver]

This is just normal encoder delay.

[Lastique]

No. The delay is indicated by avcodec_receive_packet returning AVERROR(EAGAIN) and no packet. Subsequent calls returning packets are expected to return timestamps that were passed on input.

As it is, the encoder does not introduce a delay but a negative offset in timestamps.

[Marton Balint]

Replying to Lastique:

No. The delay is indicated by avcodec_receive_packet returning AVERROR(EAGAIN) and no packet. Subsequent calls returning packets are expected to return timestamps that were passed on input.

As it is, the encoder does not introduce a delay but a negative offset in timestamps.

You misunderstand, it is indeed encoder delay, or audio priming is another name for it:

​https://developer.apple.com/library/archive/documentation/QuickTime/QTFF/QTFFAppenG/QTFFAppenG.html