[FFmpeg-user] Questions about openCORE AMR behavior

[Moritz Barsnick]

On Mon, Feb 02, 2015 at 10:30:51 -0500, Nicanor Garcia wrote:
> Currently I'm using the -b option to set the bitrate of the encoded audio,
> but I want to know what would happen if I didn't set that option? Would I
> get a multi-rate audio signal?

According to the documentation, there are constant bitrate defaults for
both audio and video:

https://www.ffmpeg.org/ffmpeg-codecs.html#Codec-Options

-b:a defaults to 128K [should that be k?] if not given,
-b:v defaults to 200k if not given.

I thought it might be codec dependant, but I can't find any
documentation on that. For example, libx264 video defaults to preset
"medium", crf 23, I believe, which is different from said 200k.

Apart from that, if you want VBR, you will needs to set some
appropriate option to trigger that (often -q/-qscale).

Cheers,
Moritz