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Stuttering with the pcHDTV-3000 + NVidia + XvMC
PostPosted: Mon Jan 09, 2006 9:21 pm Reply with quote
EvilBill
 
Joined: 09 Jan 2006
Posts: 1




I recently picked up a pcHDTV-3000 and was experiencing bad stuttering issues. After much playing around, I figured out there are three main causes of stuttering and the first one was the biggest culprit and the biggest surprise.

1) When running xine-hd with "-V xvmc" to use the NVidia card for MPEG-2 decoding, I noticed bad stuttering and snow in the picture (even in the opening animation). Changing to either "-V xv" or not specifying the video driver (so xv was used) resulted in much cleaner and smoother video. This was with both the 7676 and 8178 NVidia drivers on a Asus branded Ti4200 (Asus V9280/TD).

2) Running xine --verbose=1 will show frame skip/drop statistics and messages. There are two flavors of messages, one indicated by something like:

Code:
video_out: throwing away image with pts 2037974 because it's too old (diff : 12317).


My best guess is that it is a combination of xine timing issues and a packet arriving at the wrong time e.g. due to multipath issues. Changing my UHF antenna to one appropriate to my situation not only increased my signal strength but also my S/N ration and my multipath rejection.

Oddly, using xvmc seemed to make the junked frames worse.. that is occur more often. I am not sure there was a real correlation there but it seemed to be the case.

No one really mentions this but when you tune into a channel in xine with the verbose option, you will see a couple of lines like this:

Code:

input_dvb: Signal strength: 62979
input_dvb: Signal/Noise Ratio: 64469


When I had a S/N Ration less than 60000 there seemed to be many problems throughout the stream. When it is higher than that there are startup frames that get junked but afterward it seems to stabilize.

3)The third item is the good old skipped frames due to the computer not being able to handle the data. On my old Athlon 1.4GHz and the two items above resolved, I get from 0-40 out of 200 frames skipped. It is higher than I would like but still watchable.

In conclusion, while you are always very strongly encouraged to use xvmc, if you are having problems don't rule out that it is causing the problems.
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Re: Stuttering with the pcHDTV-3000 + NVidia + XvMC
PostPosted: Tue Jan 10, 2006 11:09 am Reply with quote
Scott Larson
 
Joined: 15 Oct 2003
Posts: 713
Location: Portland, OR




EvilBill wrote:
Code:
video_out: throwing away image with pts 2037974 because it's too old (diff : 12317).


My best guess is that it is a combination of xine timing issues and a packet arriving at the wrong time e.g. due to multipath issues.

Multipath only corrupts packets. xine is throwing away the image because it realized the timestamp (PTS) on the image has already passed. Displaying this image will cause audio/visual sync problems since the audio is already past the time when this frame would have been displayed.

This will happen even on the fastest systems sometimes. The only way to eliminate it completely is to disable everything else on the system (including cron) so nothing else will compete for the CPU. Fortunately a dropped frame now and then doesn't look that bad.
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Stuttering with the pcHDTV-3000 + NVidia + XvMC
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