[mythtv-users] 32khz AC3 Streams was: Sound problem with AC3 passthrough

Meatwad meatwad.get.the.honeys at gmail.com
Wed Jun 7 04:20:49 UTC 2006


Rob Baumstark wrote:

> Just let me confirm this, this statement confuses me a little,
> "mplayer and myth pass perfect 48k with ALSA:default"
> 
> Now for the sound to play back properly, there are really only a few
> things that could be occuring.
> 1. your hardware is capable of passthrough of a 32khz AC3
> 2. your hardware/software is decoding 32khz AC3 -> PCM, resampling,
> and out-putting PCM.
> 3. your hardware/software is decoding 32khz AC3, resampling, and
> re-encoding into AC3 to output at 48khz.
> 
> What I posted up there can't be turned into 48khz anything without
> decoding the AC3 (well - anything except chipmunk-mode, which is what
> I get).  I'm  curious as to what your receiver is indicating while you
> say that its working.

ALSA is resampling to 48k because my Denon 3806 on-screen display is 
showing PCM 48,000 but some funkyness has happened between now and then

first, i tried -ao alsa:device=default (ok)

then i tried above with -ac hwac3 (still ok) as seen in the second 
bracket of output

i removed liba52 from system and tried it (strangely, still ok) the 
output from mplayer is not listed below from this test but it DID work fine

HOWEVER, i reinstalled liba52, rebooted for kicks and grins, recompiled 
myth fron the .19-fixes SVN branch after pulling in the recent libmythtv 
fixes to test other things and tried your clip again

WITHOUT -ac hwac3, plays fine (see third block of output)
WITH -ac hwacs, jittery scratchy garble which could only be 32k arriving 
at the receiver (see 4th block of output)

i'm kinda stumped right now and my head is bobbing so i'll continue 
tommorrow afternoon when i can focus alittle more
--
mw


$ mplayer -vo xv -ao alsa:device=default ~/test.mpg
<snip>
==========================================================================
Opening audio decoder: [liba52] AC3 decoding with liba52
No accelerated IMDCT transform found
AC3: 2.0 (stereo)  32000 Hz  320.0 kbit/s
No accelerated resampler found
AUDIO: 32000 Hz, 2 ch, s16le, 320.0 kbit/31.25% (ratio: 40000->128000)
Selected audio codec: [a52] afm:liba52 (AC3-liba52)
<snip>
Checking audio filter chain for 32000Hz/2ch/s16le -> 32000Hz/2ch/s16le...
AF_pre: 32000Hz/2ch/s16le
alsa-init: 1 soundcard found, using: default
alsa: 32000 Hz/2 channels/4 bpf/43688 bytes buffer/Signed 16 bit Little 
Endian
AO: [alsa] 32000Hz 2ch s16le (2 bps)
Building audio filter chain for 32000Hz/2ch/s16le -> 32000Hz/2ch/s16le...
Starting playback...
VDec: vo config request - 720 x 480 (preferred csp: Planar YV12)
VDec: using Planar YV12 as output csp (no 0)
Movie-Aspect is 1.33:1 - prescaling to correct movie aspect.
VO: [xv] 720x480 => 720x540 Planar YV12
alsa-space: xrun of at least 0.079 msecs. resetting stream2.0% 3 0
TS_PARSE: COULDN'T SYNC-0.003 ct: -0.185 970/970 19%  1%  1.5% 10 0
A:  59.8 V:  59.8 A-V:  0.007 ct: -0.181 978/978 19%  1%  1.5% 10 0
alsa-uninit: pcm closed

$ mplayer -vo xv -ao alsa:device=digital -ac hwac3 ~/test.mpg
<snip>
==========================================================================
Forced audio codec: hwac3
Opening audio decoder: [hwac3] AC3/DTS pass-through S/PDIF
No accelerated IMDCT transform found
hwac3: switched to AC3, 320000 bps, 32000 Hz
AUDIO: 32000 Hz, 2 ch, ac3, 320.0 kbit/31.25% (ratio: 40000->128000)
Selected audio codec: [hwac3] afm:hwac3 (AC3 through S/PDIF)
<snip>
Checking audio filter chain for 32000Hz/2ch/ac3 -> 32000Hz/2ch/ac3...
AF_pre: 32000Hz/2ch/ac3
alsa-init: 1 soundcard found, using: digital
alsa: 32000 Hz/2 channels/4 bpf/40960 bytes buffer/Signed 16 bit Little 
Endian
AO: [alsa] 32000Hz 2ch ac3 (1 bps)
Building audio filter chain for 32000Hz/2ch/ac3 -> 32000Hz/2ch/ac3...
Starting playback...
VDec: vo config request - 720 x 480 (preferred csp: Planar YV12)
VDec: using Planar YV12 as output csp (no 0)
Movie-Aspect is 1.33:1 - prescaling to correct movie aspect.
VO: [xv] 720x480 => 720x540 Planar YV12
TS_PARSE: COULDN'T SYNC 0.000 ct: -0.185 970/970 19%  1%  0.7% 4 0
A:  59.8 V:  59.8 A-V: -0.002 ct: -0.186 978/978 19%  1%  0.7% 4 0
alsa-uninit: pcm closed

$ mplayer -vo xv -ao alsa:device=default ~/test.mpg
<snip>
==========================================================================
Opening audio decoder: [liba52] AC3 decoding with liba52
No accelerated IMDCT transform found
AC3: 2.0 (stereo)  32000 Hz  320.0 kbit/s
No accelerated resampler found
AUDIO: 32000 Hz, 2 ch, s16le, 320.0 kbit/31.25% (ratio: 40000->128000)
Selected audio codec: [a52] afm:liba52 (AC3-liba52)
<snip>
Checking audio filter chain for 32000Hz/2ch/s16le -> 32000Hz/2ch/s16le...
AF_pre: 32000Hz/2ch/s16le
alsa-init: 1 soundcard found, using: default
alsa: 32000 Hz/2 channels/4 bpf/43688 bytes buffer/Signed 16 bit Little 
Endian
AO: [alsa] 32000Hz 2ch s16le (2 bps)
Building audio filter chain for 32000Hz/2ch/s16le -> 32000Hz/2ch/s16le...
Starting playback...
VDec: vo config request - 720 x 480 (preferred csp: Planar YV12)
VDec: using Planar YV12 as output csp (no 0)
Movie-Aspect is 1.33:1 - prescaling to correct movie aspect.
VO: [xv] 720x480 => 720x540 Planar YV12
alsa-space: xrun of at least 8.971 msecs. resetting stream?,?% 0 0
TS_PARSE: COULDN'T SYNC-0.004 ct: -0.187 970/970 22%  1%  1.7% 5 0
A:  59.8 V:  59.8 A-V: -0.015 ct: -0.193 978/978 22%  1%  1.7% 5 0
alsa-uninit: pcm closed

$ mplayer -vo xv -ao alsa:device=default -ac hwac3 ~/test.mpg
<snip>
==========================================================================
Forced audio codec: hwac3
Opening audio decoder: [hwac3] AC3/DTS pass-through S/PDIF
No accelerated IMDCT transform found
hwac3: switched to AC3, 320000 bps, 32000 Hz
AUDIO: 32000 Hz, 2 ch, ac3, 320.0 kbit/31.25% (ratio: 40000->128000)
Selected audio codec: [hwac3] afm:hwac3 (AC3 through S/PDIF)
<snip>
Checking audio filter chain for 32000Hz/2ch/ac3 -> 32000Hz/2ch/ac3...
AF_pre: 32000Hz/2ch/ac3
alsa-init: 1 soundcard found, using: default
alsa: 32000 Hz/2 channels/4 bpf/43688 bytes buffer/Signed 16 bit Little 
Endian
AO: [alsa] 32000Hz 2ch ac3 (1 bps)
Building audio filter chain for 32000Hz/2ch/ac3 -> 32000Hz/2ch/ac3...
Starting playback...
VDec: vo config request - 720 x 480 (preferred csp: Planar YV12)
VDec: using Planar YV12 as output csp (no 0)
Movie-Aspect is 1.33:1 - prescaling to correct movie aspect.
VO: [xv] 720x480 => 720x540 Planar YV12
TS_PARSE: COULDN'T SYNC-0.003 ct: -0.189 970/970 21%  1%  0.7% 7 0
A:  59.8 V:  59.8 A-V: -0.014 ct: -0.195 978/978 21%  1%  0.7% 7 0
alsa-uninit: pcm closed


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