At Tue, 18 Nov 2008 19:08:18 +0800,
Wu Fengguang wrote:
>
> On Tue, Nov 18, 2008 at 11:57:08AM +0100, Takashi Iwai wrote:
> > At Tue, 18 Nov 2008 16:57:16 +0800,
> > Wu Fengguang wrote:
> > >
> > > To play a 3+ channels LPCM/DSD stream via HDMI,
> > >
> > > - HDMI sink must tell HDMI source about its speaker placements
> > > (via ELD, speaker-allocation field)
> > > - HDMI source must tell the HDMI sink about channel allocation
> > > (via audio infoframe, channel-allocation field)
> > >
> > > (related docs: HDMI 1.3a spec section 7.4, CEA-861-D section 7.5.3 and 6.6)
> > >
> > > This patch attempts to set the CA(channel-allocation) byte in the audio infoframe
> > > according to
> > > - the number of channels in the current stream
> > > - the speakers attached to the HDMI sink
> > >
> > > A channel_allocations[] line must meet the following two criterions to be
> > > considered as a valid candidate for CA:
> > > 1) its number of allocated channels = substream->runtime->channels
> > > 2) its speakers are a subset of the available ones on the sink side
> > >
> > > If there are multiple candidates, the first one is selected. This simple
> > > policy shall cheat the sink into playing music, but may direct data to the
> > > wrong speakers.
> > >
> > > Sorry, this last step is not obvious to me. Any domain experts, please?
> >
> > The problem is that the speaker positioning isn't defined in the ALSA
> > API yet. I think your implementation will work in practice.
>
> OK. Let's forget it until (possibly) some one complains ;-)
>
> > > +static struct cea_channel_speaker_allocation channel_allocations[] = {
> > > +/* channel number: 8 7 6 5 4 3 2 1 */
> >
> > Do we need to set ca_index explicitly?
> > Any case ca_index != array index?
>
> Yes, since we stop at the first matching item, the lines could be
> reordered somewhere to give priority to some popular ones.
Fair enough. One thing I forgot is the initialization style.
Try to initialize in C99 style, something like
static struct cea_channel_speaker_allocation channel_allocations[] = {
{ .ca_index = 0x00,
.speakers = { ..... } },
{ .ca_index = 0x01,
.speakers = { ..... } },
...
};
You can indent as you like, though.
thanks,
Takashi
_______________________________________________
Alsa-devel mailing list
Alsa-devel@xxxxxxxxxxxxxxxx
http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
