[mythtv] frame dropping with ticket #5900 (AC3-enc) + #6279 (soft-volume)

[Markus Schulz]

hello,

i've much trouble with heavy judder cause of frame dropping.
I'm using trunk with vdpau (2xadvanced) with a 9400GT (latest stable 
nvidia-cs) with mostly SD.

At first i think the videoout_vdpau should return true on 
hasHWAcceleration() to prevent additional juddering (see void 
NuppelVideoPlayer::AVSync(void) function):

diff --git a/mythtv/libs/libmythtv/videoout_vdpau.h 
b/mythtv/libs/libmythtv/videoout_vdpau.h
index a7f195b..b8159b9 100644
--- a/mythtv/libs/libmythtv/videoout_vdpau.h
+++ b/mythtv/libs/libmythtv/videoout_vdpau.h
@@ -49,6 +49,10 @@ class VideoOutputVDPAU : public VideoOutput
         { return m_codec_id > kCodec_NORMAL_END; }
     void SetNextFrameDisplayTimeOffset(int delayus);

+    /// \brief Return true if HW Acceleration is running
+    virtual bool hasHWAcceleration(void) const { return true; }


This changes the Frame drops to skipping A/V wait (less of judder).

But i don't understand why i still got a lot of:
2009-07-19 18:31:03.311 NVP(1): Video is 3.22685 frames behind audio 
(too slow), skipping A/V wait.                                   
2009-07-19 18:31:05.891 NVP(1): Video is 3.20082 frames behind audio 
(too slow), skipping A/V wait.                                   
2009-07-19 18:31:05.911 NVP(1): Video is 3.1756 frames behind audio (too 
slow), skipping A/V wait.                                    
'video_output' mean = '40207,36', std. dev. = '25365,55', fps = '24,87'                                                               
2009-07-19 18:31:07.060 NVP(1): Video is 3.02257 frames behind audio 
(too slow), skipping A/V wait.                                   
2009-07-19 18:31:07.064 NVP(1): Video is 3.17943 frames behind audio 
(too slow), skipping A/V wait.                                   
2009-07-19 18:31:07.070 NVP(1): Video is 3.0658 frames behind audio (too 
slow), skipping A/V wait.                                    
2009-07-19 18:31:09.553 NVP(1): Video is 3.2014 frames behind audio (too 
slow), skipping A/V wait.                                    
2009-07-19 18:31:09.556 NVP(1): Video is 3.26355 frames behind audio 
(too slow), skipping A/V wait.
2009-07-19 18:31:09.570 NVP(1): Video is 3.07265 frames behind audio 
(too slow), skipping A/V wait.
'video_output' mean = '39984,38', std. dev. = '22128,54', fps = '25,01'

i can reproduce the problem with the following setup:
- softvolume enabled (mixer = software)
- internal volume completely disabled
- internal volume enabled with alsa:default as mixer (useless cause of 
ac3-enc and passthru)

and all interlaced stuff or HD-1080p stuff. Progressive avi with 25FPS 
shows no frame drops.


the problem arrived with ffmpeg sync (approx. cause i've build no 
version after ~20650 and before ffmpeg sync).

Can someone help me to analyze this problem? Which change can introduce 
such a behavior?

msc