[mythtv-users] SPDIF passthrough problems / VDPAU problems

[mythtv at thestack.de]

Am 01.02.2012 08:38, schrieb Jean-Yves Avenard:
> On 31 January 2012 22:29,  <mythtv at thestack.de> wrote:
>> Hi,
>>
>> for the audio problems:
>>
>> My HTPC running mythtv 0.24.1 (now upgraded to 0.24.2) is connected 
>> to
>> an AVR via optical SPDIF. Here's my audio settings:
>>
>> - Audio output device: "ALSA:hw:CARD=CMI8738,DEV=2" (also tried
>> "ALSA:iec958:CARD=CMI8738,DEV=0" here)
>
> this is not a valid device, and not one you want to use.

Why isn't this valid? I pressed the scan button and tried several 
devices to find those using iec958 output which are the two mentioned 
above.

>> - DD and DTS checked in capabilities
>> - Speaker configuration: 5.1
>> - Upmixing disabled
>> - Advanced Audio Config:
>
> What is it with people touching advanced audio config...

Many forum posts stated that this would help. However of course I also 
tried disabling the advanced audio config stuff.

>>  - Digital output device: ALSA:iec958:{ AES0 0x02 } (also tried 
>> without
>> this enabled)
>
> leave the advanced settings untouched, everything should be unchecked

As I wrote that didn't help either.

> Read the wiki and the documentation.
>
> You have a Scan Audio Device button, press it then select an audio
> device that it found.
>
> If using SPDIF, it will have iec958 in its name

I did. That doesn't work for me.

>> - Internal mixer disabled
>>
>> All kind of two channel audio works fine but for multichannel audio
>> (both DD/AC3 and DTS) I only get choppy output. Changing Speaker 
>> config
>> to Stereo or disabling the digital audio device / advanced settings
>> doesn't help oder I even get no sound at all.
>
> you must select 5.1 in the speaker config and have AC3 and DTS 
> checked...

That's what I wrote.

> Forget any ancient documentations that would have stated that for
> digital passthrough you would have to use stereo. Those documentation
> are obsolete and it hasn't been the case for years.
>
>> In VLC media player and mplayer the same media files are working
>> perfectly. I thought the "reenc 0" in the logs means everything is 
>> right
>> but it seems it's not.
>
> what audio device are you using in VLC or mplayer? the same audio
> device will work in myth in the same fashion

Yes, the same audio device works in VLC but *not* in myth.

>> ALSA lib pcm_dmix.c:1018:(snd_pcm_dmix_open) unable to open slave
>> 2012-01-30 12:05:19.018 ALSA, Error:
>> snd_pcm_open("dmix:CARD=CX8811,DEV=0"): No such file or directory
>> ALSA lib pcm_dsnoop.c:551:(snd_pcm_dsnoop_open) The dsnoop plugin
>> supports only capture stream
> [snip]
>
> you should never see those messages when starting a playback.
> Only when you have enabled audio log and are scanning for audio
> devices, it goes through all the ones found by ALSA, and myth filters
> them as required

So what could cause that? I don't have any extra audio logging enabled.

>> 2012-01-30 12:12:20.150 AO: Opening audio device
>> 'hw:CARD=CMI8738,DEV=2' ch 2(6) sr 48000 sf signed 16 bit reenc 0
>> 2012-01-30 12:12:20.152 ALSA, Error: Setting hardware audio buffer 
>> size
>> to 128
>> 2012-01-30 12:12:20.152 ALSA, Error: Error opening
>> /proc/asound/card0/pcm2p/sub0/prealloc: Permission denied.
>> 2012-01-30 12:12:20.152 ALSA, Error: Try to manually increase audio
>> buffer with: echo 128 | sudo tee 
>> /proc/asound/card0/pcm2p/sub0/prealloc
>
> Well, here would be a useful hint to start with on what you have to 
> do
>
>
>> 2012-01-30 12:12:20.152 ALSA, Error: Unable to sufficiently increase
>> ALSA hardware buffer size - underruns are likely
>
>>
>> The last line then gets repeated VERY often (about 25 times per 
>> second,
>> maybe that's one line for each frame?)
>
> well, you have an issue in your video file here and myth is unable to
> decode it with VDPAU

That video file does play fine using vdpau but it just produces those 
log messages.

>> Manually increasing audio buffer with: echo 128 | sudo tee
>> /proc/asound/card0/pcm2p/sub0/prealloc didn't help.
>
> the issue you have reported so far is an issue with the media being
> played, not your audio config (even though this one needs adjusting)

Why does it appear for ALL kind of media files then?