iplayer audio to lpcm

[Christopher Woods]

On 8 November 2014 13:32:51 Owen Smith <owen.smith at cantab.net> wrote:

> Blasted mailing list, I sent the message below as a personal reply, AGAIN. 
> I simply cannot get my brain to accept how this list works. I'm on half a 
> dozen other mailing lists all of which work the other way round ie. replies 
> go to the list. Mutter.
> --
> Owen Smith <owen.smith at cantab.net>
> Cambridge, UK
>
> On 8 Nov 2014, at 12:54, Owen Smith <owen.smith at cantab.net> wrote:
>
> > This is decoding a lossy format (AAC), not encoding. Provided there are 
> no digital volume controls or similar being applied, the results should be 
> identical regardless of which software is used to decode it. It's the 
> definition of AAC that dictates what an AAC stream decodes to. Encoding yes 
> there is plenty of room for different implementations to produce different 
> results, but not decoding. Otherwise it wouldn't be a correct decode of the 
> AAC.
> > --
> > Owen Smith <owen.smith at cantab.net>
> > Cambridge, UK
> >
> > On 8 Nov 2014, at 12:26, Jim Lesurf <jcgl at audiomisc.co.uk> wrote:
> >>
> >> Thanks, I'll look at the above. One of the things I'm curious about is the
> >> relative performance (in terms of quality, etc) of ffmpeg versus avcodec. I
> >> come to this from being a long term user of ffmpeg, but knowing nothing
> >> about the forking or its effects. Given my past I tend to go for using
> >> ffmpeg as my first intent. But would/will change if it is advantageous.
> >>
> >> Jim
> >>
>
>

Bringing this sharply back on topic...

IIRC, DTT, DSAT and iPlayer are basically fed with the same quality source. 
iPlayer caps live from the full fat source signal, with automation to tell 
it when to start and stop, except where something has been preloaded for 
immediate availability. Not intimately familiar with the latest incarnation 
setup but I'll read some docs and confirm with people who do, I'm also 
curious now.

IMO any significant difference in sound is going to be down to relative 
codec efficiency, not due to huge differences in the TX chain. iPlayer 
desktop uses AAC-LC, DSAT is MP2 and AAC for HD, DTT the same albeit at 
lower bit rates.