[mythtv-users] Playback problem -- random short pauses

[Don Lewis]

On 23 May, Michael T. Dean wrote:
> On 05/23/2011 12:07 PM, Paul Gardiner wrote:
>> On 23/05/2011 16:42, Michael T. Dean wrote:
>>> If you want to prevent all the "random short pauses" that occur during
>>> playback, simply change your Playback Profile group such that you never
>>> use VDPAU decoding.  Use ffmpeg decode with VDPAU rendering, and all
>>> works well.  The only pauses you'll see is the at-recording-start/stop
>>> pauses (which is a completely separate and unrelated problem).
>> Confused! I thought it was the at-recording-start/stop pauses we
>> were talking about. I don't believe I see any other type of
>> pause on my system, and I'm using VDPAU decode, so I guess
>> I must be lucky.
> 
> There are 3 types of pauses that occur during playback with current 
> MythTV on a properly-configured system.  These are distinct and 
> unrelated issues.  This thread has various users talking about the 3 
> different issues and providing information that seems contradictory, but 
> that is well explained by the fact that they're discussing very 
> different things.  The 3 issues are:
> 
> 1) Short pauses that occur when the UI thread is blocked during 
> qapp-processEvents() call.  This is the at-recording-start/stop pauses I 
> mention.  These will occur regardless of which decoder/renderer you use.
> 
> 2) Short pauses that occur due to video buffer starvation due to a 
> combination of ffmpeg demux (reading data from the file to pass to the 
> decoder) and vdpau decode.  These pauses occur at "random" intervals 
> during playback--even when nothing is happening on the backend or the 
> frontend.  These can be worked around by not using VDPAU decode--instead 
> use ffmpeg decode.
> 
> 3) Short pauses that occur at Live TV program boundaries.  These may or 
> may not be related to #1, and I know nothing at all about them because I 
> don't use Live TV.

4) Short pauses while watching a previously recorded program that occur
when mythbackend starts and/or stops recording.

I have problems #1 and #4.  I don't see #2 and I don't use Live TV.

There have been times when I've had as many as four recordings in
progress, and is long as recordings are not starting or stopping,
playback is flawless.  A single recording starting or stopping (I don't
happen to know which) on an otherwise idle system causes playback
pauses.

> So, if you use ffmpeg decode (rather than VDPAU decode), you'll only see 
> #1 and #3.  Issue #1 only occurs when the backend starts or stops a 
> recording (so generally happens on the top of or half past the hour, and 
> only while you're actually recording shows while watching other 
> recordings).  Issue #3 only occurs in Live TV, as it's a Live TV 
> specific thing, and only occurs on program boundary/when the backend 
> stops and starts the Live TV recordings.
> 
> Also, it's possible that specifying videobuffersize=32 in the filter 
> section of the VDPAU-decode playback profile may work around the VDPAU 
> video buffer starvation issue (#2), but that may "undo" all the changes 
> that have allowed use of VDPAU on low-memory video cards (like 256MB 
> cards)--you'll likely need a 512MB or greater card.  We're still testing 
> this, and would appreciate users providing feedback about whether it 
> helps or not.  This may be why you're not seeing the VDPAU issues, Paul 
> (so please let us know if you have specified videobuffersize or other 
> filters).

I'll try experimenting with VDPAU, but I think I was still using the
Nvidia 7050 onboard video, which is not VPDAU capable, when I upgraded
from 0.23 to 0.24 and started seeing the problem.  I don't think I
dropped in the GT220 until later, when I got my HD-PVR.  It's been so
long ago that I'm kind of fuzzy on the timeline at this point.