[FFmpeg-devel] Exposing preroll and remainder info for aac and mp3.

[Dale Curtis]

Hi all,

We're running into problems with leading and trailing silence due to
pre-roll and remainder with aac and mp3 encodes. To illustrate here's a
demo showing the decoded output of a couple mp3 and aac files:

http://rtoy.github.com/webaudio/codec-tests/plot-audio.html

(requires Chrome or very recent Safari). Compare the aac and mp3 results
with ogg.

We're wondering what the best approach is here. Should ffmpeg/libav be
cutting the codec specific preroll information before sending it on? Or
should we simply expose this information through say
AVCodecContext->metadata for downstream consumers to do what they wish with?

See the following for the AAC specific information:
http://developer.apple.com/library/mac/#documentation/QuickTime/qtff/QTFFAppenG/QTFFAppenG.html

The reason this is necessary is for sample accurate playback of clips which
is important for applications like WebAudio.

Has anyone looked into this before?

Thanks in advance!

- dale