[MPlayer-dev-eng] MPEG to S/PDIF passthrough

[Ilkka Karvinen]

On Thursday 06 March 2008 13:57, Ulion wrote:
> 2008/3/6, Ulion <ulion2002 at gmail.com>:
> > 2008/3/5, Ilkka Karvinen <kartsan at gmail.com>:
> > > There have been no comments on this patch. I'm wondering if there could
> > > be
> > >
> >  >  people around here who have a home theater amplifier which supports
> >  > MPEG audio? It would be interesting to hear if this feature works with
> >  > your hardware. Especially if you are running mplayer on a bigendian
> >  > machine since I can't currently test this code on a such machine.
> >  >
> >  >  If your amplifier supports AC3/DTM decoding, its DSP may also support
> >  >  MPEG audio. My old Harman Kardon amplifier uses Cirrus Logic's DSP
> >  >  which supports it and that was my initial reason to start
> >  > investigating this stuff.
> >  >
> >  >  I send attached diff that Ulion made for me if you would like to give
> >  > a try to this feature. It adds new codec hwmp3 which redirects the
> >  > MPEG frames to hardware via S/PDIF.
> >  >
> >  >  I have tested it and it works with mp3 audio files and video files
> >  > with mp3 audio track. However, some mp3 files do not work and I don't
> >  > know why. My guess is that their frames are not recognised by my
> >  > hardware. There are no similarities with the failing samples. Another
> >  > sample with equal parameters (header bits are the same) may work
> >  > flawlessly.
> >
> > found some problem about this patch:
> >
> >  in decode_audio():
> >  +  uint16_t *buf16 = (uint16_t *)buf;
> >
> >  should this be put into the while loop and looks like this:
> >
> >  +  uint16_t *buf16 = (uint16_t *)(buf + toc);
>
> I mean:
> +  uint16_t *buf16 = (uint16_t *)(buf + tot);

What is the problem?

> and there's another type value for 'MPEG-2 with extension' it should
> be 6 instead of 5.
> there's also a type value for 'MPEG-2 layer-3 low sampling frequency'
> referred by IEC 61937-4.
> should these two type be handled in the code?

Those MPEG-2 types were so rare that I didn't put them there. Actually
there was type 4 in my original implementation which is MPEG-1 layer-1
but even that I've never seen so I dropped it. I can add them to this codec
to make sure. I'm pretty sure that the documentation of the DSP in my
amplifier said it supports only MPEG-1 layer 3 so those formats were
unknown for it anyway...

Ilkka