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

[Michael T. Dean]

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.

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).

Mike