[FFmpeg-devel] audio gop_size

Michael Niedermayer michaelni
Tue Aug 24 18:21:07 CEST 2010

On Sun, Aug 22, 2010 at 04:40:54PM -0400, Justin Ruggles wrote:
> Hi,
> There are several audio codecs (such as MLP, ALS, and Speex) which
> utilize the concept of groups of frames.  For decoding, it is simple
> enough to either decode the whole group at once or decode
> frame-by-frame, but for encoding there are other issues.  This is how
> Thilo and I have implemented it in the ALS encoder we've been working
> on, and I wanted to run it by the list to make sure we're on the right
> track.
> 1) Make gop_size an audio option as well.
> alternative: The downside is that it defaults to 12, which may not be an
> appropriate default for some audio codecs.  Would changing the gop_size
> default have API implications?  Should we instead add another field for
> audio group of frames size that would default to 0 or -1?
> 2) Use an internal buffer in the encoder to store each encoded frame
> until it has enough for a group, then set coded_frame->pts appropriately
> and output the whole group.  The reason that the whole group needs to be
> encoded at once is because the container packet should always contain a
> whole group (at least this is the case for ALS and Speex).

if the container needs a "GOP" per packet and the encoder outputs a whole gop
at a time then this is semantically different
from video gops and it appears more a encoder internal structuring like mp3
or aac using short instead of long windows

Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

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