Transcoding HLS streams to MP3 output

[simoncn]

(03-03-2015 01:03)Tell Wrote:  Yes I'm gradually getting my head round these things now, the golden rule to me seems to be to unpack the encoded stream and then repack it to the level of quality you require require. 320 AAC is going to be 320 MP3 for sure. If one is keeping a recorded programme from say AAC audio or TV stream then you encode it to FLAC so you keep a replica of what it was like on the day and on a player that can handle FLAC you can always re-create what you recorded in AAC at the time.

So yes 320 would be 320 since you can't go higher in standard MP3, 192 AAC if such a thing exists on the BBC system would be probably 320 in MP3. So in MP3 you want that added level up lift from a table. There are tables of equivalence of AAC to MP3 on line so possible that up lift is required for live materiel. I normally do a rule of thumb guess.

Perhaps you could assume that all UK HLS streams will require 320 MP3. Whilst the non UK ones 48k and 96k you could put at 192 MP3 perhaps as a rule of thumb.

This is more desirable than a bit by bit rate matching since you need more for MP3 to package up what has been encoded in AAC which will inherently sound better at that bit rate.

It isn't as easy as I expected for MinimServer to detect the bitrate of the input stream and set the output bitrate to match. This is because MinimServer might need to read and analyse a significant amount of audio data from the input stream to calculate the bitrate.

I think the best solution is to provide a new MinimServer transcoding parameter to allow the user to set the bitrate to be used for encoding the output stream.