[mythtv-users] Re: alsa support in myth (was: Latest atrpms kernel ...)

[Jarod C. Wilson]

On Thursday, Paul Jara wrote:

> On Thursday, August 28, 2003, at 05:47  AM, Michael Novich wrote:
>
>> Interestingly, trying to use an Alsa device once fixed my black video
>> problem.
>> I changed it back to /dev/dsp and the video stills shows, but no 
>> audio.
>>
>> I manually changed the player settings for mplayer (within myth) to 
>> add
>> "-ao alsa9" to the command line and voila - crystal clear sound. I'm
>> sure, however, that there is a better solution and that although I 
>> have
>> Alsa installed, OSS emulation (which is what I believe I am supposed  
>> to
>> be using) must not be working right.
>> Any way to diagnose this?
>>
>
> That's a pretty good hypothesis. I'm not sure of the best way to 
> diagnose the problem but one way I liked to do it was to use an app 
> like XMMS that (with the right plug-ins) could use both OSS and ALSA - 
> though not both at the same time. If ALSA is not working, the XMMS 
> ALSA output mode won't work but the OSS one will. Vice versa if OSS 
> emulation is not working. If you want to test this out, you'll need to 
> install the xmms-alsa plug-in that is available from repositories such 
> as freshrpms as it is not installed by default with XMMS.
>
> Since you've got a pvr-250 which also does sound (if I'm not mistaken) 
> and should therefore show up as a sound card, I'd bet there's a 
> configuration error somewhere. Things can get pretty complex when two 
> or more sound cards are installed. I'd check to see if your true sound 
> card configuration and pvr-250 sound configuration aren't conflicting 
> with eachother or otherwise mixed-up.

The PVR-250 does do audio, but it does NOT show up as a sound card. The 
audio is muxed w/the video, straight into an mpeg2 stream.

> (more commentary below in Axel's e-mail)
>
>> Here's what used to happen.
>>
>> If user mythtv ran mplayer from a shell, it would say "device not 
>> found
>> /dev/dsp" and then autmoatically print out something about finding 
>> Alsa
>> and would go ahead and use it.
>> When mythfrontend would run it, it would just not find /dev/dsp and 
>> then
>> no sound would come out. It would keep attempting to use /dev/dsp for 
>> a
>> while before dying, but the error was printed 10-20 times.
>>
>> I'm running on a pundit with a pvr-250, recording works fine (I'm sure
>> there is some tweaking left, but overall, its better than VHS, so I'm
>> not 100% worried).

Just a shot in the dark, but you did run through setup, and get to the 
point where you clicked "Finish" in the part where you tell MythTV to 
use /dev/dsp for sound, didn't you? I've seen systems, where even 
though the default setting in the setup is /dev/dsp, it didn't actually 
take hold until I went through that part of the setup and committed it 
w/a "Finish".

>> Thanks in advance for any help,
>> Michael
>>
>>> From: Axel Thimm [mailto:Axel.Thimm at physik.fu-berlin.de]
>>> Hi,
>>>
>>> taking this to the list.
>>>
>>> This request reappears every now and then. Lately Paul (Cced)
>>> checked out the situation, but he finally suggested to not
>>> include the ALSA patch (or activation?) for now in the rpms,
>>> as it didn't improve his situation.
>
> Let me elaborate a bit on this. I had a specific problem with sound in 
> MythTV. I was getting jerky live TV playback and the sound would 
> stutter. I was using OSS-emulation but had the ALSA drivers installed. 
> I thought compiling ALSA support into MythTV might remedy the 
> situation so I did just that. The situation did not get better. In 
> fact, it got a bit worse. I'm at a loss to explain why but I guessed 
> it had to do with the fact that MythTV only had preliminary, and 
> therefore a bit immature, ALSA support. I eventually stumbled on a fix 
> for my problem when I thought I'd move back to a Windows-based PVR 
> solution. I tried, but nothing came close to MythTV's level of 
> features and functionality. So, I decided to go back to Linux. I 
> reinstalled Red Hat 9, and immmediately installed MythTV from Axel's 
> repository and low-and-behold, everything worked nicely even in live 
> TV mode. I decided to leave everything as-is. As such, I haven't 
> installed the ALSA drivers nor have I bothered (of course) to 
> compile-in ALSA support into MythTV. I have noticed some drawbacks. 
> With OSS, changing channels causes the video and audio to lose sync 
> for the first initial seconds. But after those few seconds, the sync 
> is perfect again. With ALSA, there was no sync issue. And, when MythTV 
> was working properly, the MythTV OSS-emulation mode/ALSA driver 
> combination seemed more responsive to channel changes and such.
>
> Basically, my opinion for RH9 right now is to try to stick to basics. 
> Get pure OSS mode working. If you cannot, then try OSS-emulation with 
> ALSA drivers. If there are still problems, then I'm not certain a pure 
> ALSA mode will alleviate them. There is probably something more subtle 
> going on.

Though if you want to use something like S/PDIF out to your amp, ALSA 
is the only way to go. :) I use Red Hat Linux 9 and all of Axel's 
packages, including ALSA. I'm definitely curious what benefits I might 
see if using pure ALSA mode MythTV, though I have no problems to speak 
of with my system as-is... Axel, care to spin off a test rpm w/the ALSA 
part enabled?


>>>> Now, before I used the update statement, I got a black
>>> screen, now I
>>>> see the video, but no audio. I asume the audio is the problem and I
>>>> hope the s-video out on the motherboard is working right.
>>>
>>> I forgot what your hardware was. If this is ivtv based, it
>>> sounds like some known problem which went away with the
>>> latest CVS version (rpm packaged).

Yep, I second that. Try updating your ivtv drivers.

--Jarod

-- 
Jarod C. Wilson, RHCE

Got a question? Read this first...
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MythTV, Red Hat Linux 9 & ATrpms documentation:
http://pvrhw.goldfish.org/tiki-page.php?pageName=rh9pvr250