I am trying to send an AC-3 stream via the SPDIF OUT of my sound card,
doing real-time encoding of various Jack inputs. The following recipe
ought to achieve that result, I would think, but it does not -- I get
white-ish noise in the output when alsaplayer tries to send data:
- ac3jack -o stdout | ac3dec --iec958c
- alsaplayer -F 48000 -o jack foo.mp3 (to ac3jack:Left and ac3jack:Right)
- jackstart --realtime -d alsa -C
- qjackctl (just to see what's going on)
+-------+ +------+
+----------+--PCM-->+----+--PCM-->| | | |
|alsaplayer| |jack| |ac3jack|--AC3->|ac3dec|--SPDIF-->
+----------+--PCM-->+----+--PCM-->| | | |
+-------+ +------+
Notes:
- Sending ac3dec --iec958c test.ac3 works perfectly.
- I use -C on jackstart so it won't block ac3dec from accessing the device.
- alsaplayer -F 48000 doesn't appear to make a difference.
Any ideas why this creates noise instead of a clean signal?
Thanks,
John
Jaroslav Kysela said:
> On Fri, 23 Jan 2004, John W. Cocula wrote:
>
>> Hello all,
>>
>> With the speaker-test program, why is it that I can get all six channels
>> of surround51 through my analog OUT jacks, but I can only receive the
>> front left and front right channels via the SPDIF digital OUT? (The
>> external digital decoder says it's in "stereo PCM" mode, but I'm
>> obviously
>> trying to drive all six channels, as if it were in "AC-3" mode.)
>>
>> But with xine or totem and an AC-3 source, I get full surround51 through
>> the SPDIF connector, and it switches by itself to "AC-3" mode.
>>
>> What can I do to address all surround51 channels via SPDIF OUT, with
>> means
>> other than an AC-3 source?
>
> You must use an AC-3 encoder. The S/PDIF can carry only stereo or
> compressed format (AC-3, DTS, MPEG, ATRAC) packed into the stereo stream.
>
> Jaroslav
>
> -----
> Jaroslav Kysela <[EMAIL PROTECTED]>
> Linux Kernel Sound Maintainer
> ALSA Project, SuSE Labs
>
>
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