[Libav-user] AAC encoding reliability

Claudio Freire klaussfreire at gmail.com
Wed Apr 9 20:20:50 CEST 2014

On Wed, Apr 9, 2014 at 2:02 PM, Gyula Hatalyák
<hatalyak.gyula at artklikk.hu> wrote:
> Hi!
> I would like to ask from which version of ffmpeg is built-in AAC encoding
> reliable?

Tip is not reliable yet, but there is a patch[0][1] that makes it
quite reliable.

Beware, though, that patch makes M/S auto-encoding the default, and it
still has some bugs. You need to specify -stereo_mode off  (or maybe,
just maybe -stereo_mode on is enough to keep the bugs out). I'm pretty
sure -stereo_mode off is as stable as you can get (I've encoded hours
and hours and no artifacts there), but it's less efficient than many
other implementations - due to precisely M/S coding being off.

> Is it still in experimental state?

It's not for me to decide, but I hope after that patch becomes final
and stable enough, it will stop being so.

> What fixes happened recently?

The patch addresses bugs in rate control, bit allocation at high bit
rates, M/S encoding bugs, bit allocation efficiency in general,
clipping due to quantization noise, and implements VBR encoding.

> Should I use libvo codec instead?
> Which is recommended?

While the mentioned patch improves things a lot (and IMHO it's better
than FAAC at least), in the short term I'd still suggest not using it
for productive purposes.

[0] https://trac.ffmpeg.org/ticket/2686
[1] https://trac.ffmpeg.org/attachment/ticket/2686/aac-improvements-wip-v8.patch

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