Audio bit rate settings

[dinkypumpkin]

On 07/02/2013 11:25, Kapitano wrote:
> On 2/7/2013 13:05 PM, Heff wrote:
>> However, each download I do has very low bitrate audio. Even on the
>> flashhd quality level, downloads have 96kbps audio, which sounds
>> terrible!
>>
>> It appears that ffmpeg/rtmp or something converts the downloaded flv
>> to mp4, which I'm guessing effects the audio quality too. Is there a
>> way to adjust the default audio conversion setting so that the final
>> video file contains something like 320kbps audio?
>>
>
> IIRC, GiP uses ffmpeg to *extract* the audio, not convert it to a
> different format. The same for the video.

Yep.  get_iplayer does not transcode.  Audio in == Audio out.

> The BBC uses FLV as a container for the MP4 file (for no good reason
> that I can see), and GiP just takes the MP4 out. For radio files,
> they're AAC inside FLV...which is inside an M4A container, which is the
> name for MP4 with only audio. Still with me? :-).

Why FLV?  Because the Beeb uses Flash Media servers, and Adobe says so. 
  And the FLV isn't inside an M4A container - see below.

> (I download radio using the --raw switch, which takes the FLV out of the
> M4A, then I use a program called FLV-Extract to get the AAC out of the
> FLV. Complicated, but it works.)
>
> BTW, if I'm talking rubbish and anyone can correct me, please do.

The --raw option doesn't "take the FLV out of the M4A".  The --raw 
option tells get_iplayer to skip re-muxing (via ffmpeg) the audio/video 
streams from the downloaded FLV file into an M4A file (audio file with 
MP4 container).  All of the flash* modes are downloaded to FLV files and 
then re-muxed if required.  You should be able to play the FLV without 
extracting the AAC stream.  Unless you need to extract the AAC for some 
other reason, of course.

> 96kbps shouldn't sound terrible, especially if the audio of the video is
> in AAC format. It isn't wonderful quality, but it's perfectly good for
> speech and okay for music. So maybe the problem is your audio playback
> equipment? You might have a bad soundcard, or it might be playing back
> too loud and distorting?
>
> 320kbps is much higher than a tv show needs - anything higher than 192
> and I don't think you'd notice the difference. You *might* want 320 for
> classical music - Radio 3.

OP: keep in mind is that the streams available to get_iplayer are 
intended for an in-browser Flash player or a phone, so high quality 
audio isn't exactly a priority.