Some Stuttering Observations... Make that Observations of Stuttering

[Tahoe Girl]

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

[blade]

I've never used placeshifter, but isn't your server way underpowered for the task? The server has to transcode the video to a more compressed format on the fly so that it can be streamed across the internet and 500mhz would appear to be far too little power to do the job.

[Tahoe Girl]

Well I guess that's a fair question, but since I can only be in one place at a time, I have no idea what the CPU utilization is on that system when I'm viewing things on PS here !

I'm only guessing, but I would think the client on this end sees frames being delivered at a particular rate, and is not necessarily aware as to whether any delay is due to a slow server or a slow internet connection. All I can say for certain is that from what I can see on this end, it really looks like a problem where PS lets the video buffer utilization drop to too low a level.

[ke6guj]

Oh yah, way under powered for placeshifting. Transcoding on-the-fly takes horsepower, plan on 2gigs+ for best results. On my sempron 3100+, I'd see CPU% at more than 50%. It'll stay at 100% until it fills up the buffer, then it will drop down slightly.

To test it, you could fire up the placeshifter at the house and adjust the placeshifter client settings to transcode without having to leave the house.

[Tahoe Girl]

Thanks, I will give that a try.

[millers_35]

This may be a stupid question but how do you increase the buffer size? And whenever I push pause it will buffer up for only like 20 seconds and then its like it just stops buffering.

Miller

[Tahoe Girl]

Come on, there really are no stupid questions .

If you read enough of the posts to these forums, you pick up little tidbits every so often. You need to edit the SageTVPlaceshifter.properties file and insert a line like this:

video_buffer_size=32000000

In this case, the buffer size is being set to 32MB (well 32x1024x1024 would probably be the usual interpretation of 32MB, but I was just being lazy). I have no idea what the range of allowable values is; I am running with 64000000 at the moment and that didn't seem to break it.

BTW, the properties file is in the same directory as the executable (SageTVPlaceshifter.exe). If you don't know where it was installed, right mouse click on your SageTV icon, select properties, and then press the Find Target button.

[Tahoe Girl]

Originally Posted by ke6guj

Oh yah, way under powered for placeshifting. Transcoding on-the-fly takes horsepower, plan on 2gigs+ for best results. On my sempron 3100+, I'd see CPU% at more than 50%. It'll stay at 100% until it fills up the buffer, then it will drop down slightly.

To test it, you could fire up the placeshifter at the house and adjust the placeshifter client settings to transcode without having to leave the house.

Since I have yet to follow up on this, I thought it would be important to reply in case some else is experiencing issues similar to mine. As has been pointed out, the system which is running as my SageTV server is underpowered with regards to performing the necessary transcode processing. However, at this time this is the system that I am stuck with.

FWIW, this system is more than adequate when used with a media extender because the transcode processing does not take place on the server. This means that I get all the functionality that I desire on my televisions to which media extenders are connected. My issues involved poor performance when attempting to run a remote place shifter client.

At this time, I have some new information which may be useful to others with underpowered servers. I have found that if I record programs using a really low quality setting (VCD), that my server does not have to work as hard to transcode the file records before sending them to the client. In my case, recording at a low quality setting seems to have no effect on the quality of the picture received at the client, because of the fact that the data link at the remote location is severely limited (about 350kbs, the fastest DSL I can get at this location). Since SageTV is forced to reduce the quality of the transmitted images to even get the data across this slow link in a timely fashion (i.e. streaming video), nothing seems to be lost by having recorded it using a low quality setting.

So, if you’re having stuttering issues using place shifter, you might try recording on your server using a lower quality setting.

Hope this helps someone .

T.G.