[mythtv-users] MythTV 0.24 HDMI audio problem

John P Poet jppoet at gmail.com
Thu Dec 9 15:47:12 UTC 2010

On Wed, Dec 8, 2010 at 11:18 PM, Jean-Yves Avenard <jyavenard at gmail.com> wrote:
> Hi
> On 9 December 2010 16:56, John P Poet <jppoet at gmail.com> wrote:
>> When I kick on timestretch, the pre-amp switched from showing Dolby
>> Digital 5.1, to PCM 2.0 and only the two primary speakers are used --
>> the others are quiet.  This make me think myth is trying to use LPCM,
>> but it is not making it to my pre-amp.
> If you haven't checked the "Stereo PCM" flag in the advanced option
> and you are using an hdmi output (or an audio device reporting more
> than 2 channels), then decoded AC3 won't be re-encoded as AC3, but
> instead passed as multichannels LPCM ; no point re-encoding as it only
> adds extra audio losses and is slower.
> Mind you, depending on your amplfier, not all accepts multichannels
> LPCM. I know that the yamaha one I use for my main frontend, when I
> pass it 5.1 PCM, all I can hear is the left and right front channel
> (which is the reason I added that "Stereo PCM" flag, I needed it)
>> When I run alsamixer it lists ALL the outputs from the nvidia GT220
>> card as being S/PDIF.  Is that correct?  I would half expect HDMI to
>> be different from S/PDIF.
> that's how it shows mine too. doesn't bother me too much. It does
> bother me that it shows 4 spdif device there and I have no clue what
> they are there for
>> I have not tried your latest updates yet.  Is multi-channel ( > 2 )
>> LPCM working for you?
> well, that's the embarassing thing: my last fix to enable LPCM to be
> used, revealed another bug.
> If you use the upmixer, if 2 channels audio is upmixed as 6 channels
> audio, and you have LPCM ; then it's all screwed up.
> I believe the issue is related to the timestamp calculation, and it
> doesn't handle properly the fact that the audio stream is suddenly 3
> times bigger ; in turn I get "Waiting for video ..."
> When LPCM wasn't in used, and instead audio was re-encoded to AC3, it
> wasn't a problem because AC3 is also embedded in a stereo PCM stream,
> so the amount of data going to the audio card is the same as before it
> was upmixed...
> That's a guess anyway. I spent the whole day yesterday on this but I
> can't find why it's behaving that way...
> I'll have more time tonight, but the wife said that me staying up to
> 3AM to work on mythtv isn't acceptable anymore (and as such, can't
> wake up at 6.30 to manage the kids)


 Jean-Yves, I really do appreciate the work you do on this stuff.


A: Because it messes up the order in which people normally read text.
Q: Why is top-posting such a bad thing?

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