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

Paul Jara pjara at rogers.com
Thu Aug 28 10:57:19 EDT 2003


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.

(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).
>
> Thanks in advance for any help,
> Michael
>
>> -----Original Message-----
>> From: Axel Thimm [mailto:Axel.Thimm at physik.fu-berlin.de]
>> Sent: Thursday, August 28, 2003 3:49 AM
>> To: Michael Novich
>> Cc: Paul Jara; mythtv-users at mythtv.org
>> Subject: alsa support in myth (was: Latest atrpms kernel ...)
>>
>>
>> Hi,
>>
>> taking this to the list.
>>
>> On Wed, Aug 27, 2003 at 07:42:39PM -0400, Michael Novich wrote:
>>> Ok, its almost done. I found an update statement to set
>> mythtv to use
>>> alsa, but alas, alsa is not compiled as an option into the
>> myth distro
>>> available through apt-get. Any idea why?  That's the complain that
>>> comes up when trying to play video.
>>
>> 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.

>> I don't know, what the benefits of the native ALSA support
>> really are (probably less overhead and better latency I
>> suppose), but usually alsa in mythtv is not considered as a necessity.
>>
>> If the patch/activation has no drawbacks (e.g. not-ALSA
>> supported soundcard should still work) I'd be happy to
>> include it, but since Isaac did not with 0.11, it sounds
>> maybe like being premature.
>>
>>> 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).
>> -- 
>> Axel.Thimm at physik.fu-berlin.de
>>
>
>



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