On Wed, 2012-08-22 at 15:09 -0300, Mauro Carvalho Chehab wrote:
> Em 22-08-2012 12:19, Mike Isely escreveu:
> > On Wed, 22 Aug 2012, Mauro Carvalho Chehab wrote:
> >
> >> Em 22-08-2012 07:11, Hans Verkuil escreveu:
> >>> I've added some more core profile requirements.
> >>
> >>>>
> >>>> Streaming I/O is not supported by radio nodes.
> >>
> >> Hmm... pvrusb2/ivtv? Ok, it makes sense to move it to use the alsa
> >> mpeg API there. If we're enforcing it, we should deprecate the current way
> >> there, and make it use ALSA.
> >
> > I am unaware of any ALSA MPEG API. It's entirely likely that this is
> > because I haven't been paying attention. Nevertheless, can you please
> > point me at any documentation on this so I can get up to speed?
>
>
> I don't know much about that. A grep at sound might help:
>
> $ git grep -i mpeg sound/
> sound/core/oss/pcm_oss.c: case AFMT_MPEG: return
> SNDRV_PCM_FORMAT_MPEG;
> sound/core/oss/pcm_oss.c: case SNDRV_PCM_FORMAT_MPEG: return
> AFMT_MPEG;
> sound/core/pcm.c: FORMAT(MPEG),
> sound/core/pcm.c: case AFMT_MPEG:
> sound/core/pcm.c: return "MPEG";
> sound/core/pcm_misc.c: [SNDRV_PCM_FORMAT_MPEG] = {
> sound/usb/format.c: case UAC_FORMAT_TYPE_II_MPEG:
> sound/usb/format.c: fp->formats = SNDRV_PCM_FMTBIT_MPEG;
> sound/usb/format.c: snd_printd(KERN_INFO "%d:%u:%d : unknown
> format tag %#x is detected. processed as MPEG.\n",
> sound/usb/format.c: fp->formats = SNDRV_PCM_FMTBIT_MPEG;
>
>
> >
> > Currently the pvrusb2 driver does not attempt to perform any processing
> > or filtering of the data stream, so radio data is just the same mpeg
> > stream as video (but without any real embedded video data). If I have
> > to get into the business of processing the MPEG data in order to adhere
> > to this proposal, then that will be a very big deal for this driver.
>
> I _suspect_ that it is just a matter of adding something like em28xx-audio
> at pvrusb2, saying that the format is MPEG, instead of raw PCM. In-kernel
> processing is likely not needed/wanted.
The ivtv and cx18 drivers ask the CX2341[568] to produce a raw PCM audio
stream and provide that PCM audio via the legacy /dev/video24 device,
and via ALSA as well in the case of cx18.
>From what I can tell, the pvrusb2 driver does not use the raw PCM stream
the CX23416/7 is able to produce. Instead, pvrusb2 appears to "mute"
the video and provides then whole MPEG-2 PS in radio mode. That means
there is a full MPEG-2 PS container stream with both the audio ES and
video ES in it.
If something in user-space needs to get PCM or MPEG-1 Layer 3 audio from
that pvrusb2 "audio" stream via ALSA, something is going to need to
demux the MPEG-2 PS and possibly convert to PCM. I'll bet ALSA
currently does not support that except maybe via some ALSA plug-in which
likely does not exist.
At that point, it might be easier just to use the PCM stream from the
CX23416 and add a pvrusb2-alsa module for the ALSA interface.
Regards,
Andy
> We may try to double check with Takashi during the KS media workshop.
>
> Regards,
> Mauro
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