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SageTV Placeshifter Discussion related to the SageTV Placeshifter application produced by SageTV. Questions, issues, problems, suggestions, etc. relating to the SageTV Placeshifter software application should be posted here.

 
 
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Old 11-04-2006, 06:46 PM
Tahoe Girl Tahoe Girl is offline
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Join Date: Oct 2006
Posts: 15
Some Stuttering Observations... Make that Observations of Stuttering

I am running SageTV 5.0 and PlaceShifter on a relatively slow connection (Comcast about 370kbs up and AT&T DSL about 380kbs down). Unfortunately, there's not much I can do to improve either of the connection speeds, and so I am experiencing the same stuttering issues that have been mentioned numerous times in this forum.

On the server side, I am running Win2K Pro on a 500MHZ Pentium processor with 384MB of memory (not a big system but its dedicated and runs nothing other than SageTV). The only time it appears underpowered is if I attempt to do rendering on the PC (which I don't). It drives two Media Extenders on a wireless LAN, where the PowerPC's get to do the rendering. Works great, can't tell the difference from live TV.

On the Placeshifter client side, I am running Win XP Pro on a 2.3GHZ Xeon processor with 1GB of memory.

So now for some observations:

I am not expecting great video quality at these connection speeds, but what I see that I can get by playing the "pause/play" game to allow the video buffer to fill a bit is actually surprisingly good. In fact if there's not a whole lot of motion (as in a talk show), it's not bad at all (now a basketball game... that's a whole different story, but still surprisingly good).

I have fiddled with running PS in "fixed-mode" , but to get any reasonable play time (remember "pause/play"), I need to drop it down to 10 frames/sec, and more realistically 5 FPS (which starts to get a bit herky-jerky). It actually runs best in "dynamic-mode", where PS gets to figure out how to deliver the best video quality for the available bandwidth.

So, let's talk a bit about "dynamic-mode". I read in one of these postings that the default video buffer is 1MB, however it appears obvious the PS client is a bit of an underachiever, and doesn't come close to using much of that 1MB at all. In fact, after pausing for some period of time and pressing play, PS seems bound and determined to deplete the video buffer, and actually doesn't seem to worry about how low the buffer utilization becomes until it's too late.

Once the video buffer gets down to where there's only two or three seconds of play time left, the stuttering begins. Unfortunately by this time PS is so far behind the power curve that it cannot recover without some user intervention (i.e. press pause and let the buffer fill for awhile). Well, I don't think anyone really believes that this is the way that PS ought to be used, and it is most unpleasant to try to watch a TV program this way.

So, I am wondering if the developers have considered factoring the current video buffer utilization into their dynamic algorithms ? For example, it's clear that if there's five to ten seconds worth of buffer viewing available, there is no stuttering. What if there were some defined (or parameterized) "happy values" that the algorithms attempted to manage to in addition to trying to maintain the best possible video quality for the bandwidth.

For example, some very conservative numbers might be a low utilization of 10 seconds, and a high utilization of 20 seconds. If PS could keep the steady-state utilization of the video buffer within these bounds, the "pause/play" trick pretty much proves that the stuttering problem would go away. Now doing this *might* impact the video quality , but I know that I ( and I assume many others) would consider that a small price to pay in order to be able to watch a program from beginning to end without the continual pausing to replenish the video buffer.

For the record, I have personally addressed this problem by running with a 32MB video buffer (and am about to try bumping it to 64MB). This means that I need to start viewing a program, immediately pause it, and then find something else to do for about 30 minutes while the buffer fills. It's a bit kludgy, but with 32MB I can get about 45 minutes to an hour of viewing before the stuttering begins and I have to repeat the process. I for one certainly would like to see a solution that make PS more useable.

If anyone has any thoughts or suggestions on how to approach this problem, I would appreciate your comments.

Thanks,
TG
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