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prebuffering pause questions
http://forums.linhes.org/viewtopic.php?f=17&t=8509		 Page 1 of 1
Author:  mschlott [ Tue Feb 14, 2006 11:40 pm ]
Post subject:  prebuffering pause questions
I may get beat up for bringing this up but I have a question that I can't find the aswer to.

I'm running wireless on both the front end and back end. The back end is closer to the router so it has the best signal. The frontend has to be tweaked to get a good signal.

As I increase the bitrate in the recording profile for live tv, I get more and more prebuffering pauses. The better signal I can get on the wireless, the higher, bitrate I can get without getting the prebuffering errors.

Currently I'm watching 720x480@4Kb/s with no errors for the last 30 minutes. I change the channel and all the sudden I get several prebuffering pause messages in my .xsession-errors file.

If I keep the tuner on the same channel, the prebuffering pause messages taper off and eventually go away. The higher I set my bitrate the worse this behavior gets. I also see this behavior while watching high bitrate recordings and skipping forward or backward. The recording plays fine, untill I skip forward or back.

I am assuming that mplayer is having to catch up after changing channels or skipping forward or back. My question is why does this happen? I have watched live tv with a bitrate as high as 9Mb/s as long as I don't skip.

I'm not realy looking for a fix, as I think the fix is in the network. I am just puzzled as to why this happens.
Author:  tjc [ Wed Feb 15, 2006 12:13 am ]
Post subject:  Re: prebuffering pause questions
mschlott wrote:
I may get beat up for bringing this up but I have a question that I can't find the aswer to.

I don't see why, I think a lot of people mistake the tone around here. Think brisk and distracted. Cecil only lets us bring out the truncheons for the hard cases. ;-)

mschlott wrote:
As I increase the bitrate in the recording profile for live tv, I get more and more prebuffering pauses. The better signal I can get on the wireless, the higher, bitrate I can get without getting the prebuffering errors.

That would match my expectations. Remember you're dealing with a real time activity which has a limited tolerance for stalls. Even if your average bit rate is OK, you'll get glitches if there are any long pauses, like when the connection has to be renegotiated. You can try forcing the wireless routers to use a more conservative rate and not try to negotiate up...

mschlott wrote:
Currently I'm watching 720x480@4Kb/s

You can probably dial that back to the default 480x480 and actually get better quaility... I made several HiQ experiments back in the early days and kept coming back to the default profiles. They seem to be really well tuned.

mschlott wrote:
If I keep the tuner on the same channel, the prebuffering pause messages taper off and eventually go away. The higher I set my bitrate the worse this behavior gets. I also see this behavior while watching high bitrate recordings and skipping forward or backward. The recording plays fine, untill I skip forward or back.

This probably just has to do with the fact that when you switch streams or reposition you lose any buffer backlog you have on the frontend.

mschlott wrote:
I am assuming that mplayer

Not part of the equation. TV recordings use MythTV's own internal player. The mplayer and/or xine players are only used for optical disks and other formats under the "MythVideo" plugin.

Hope this answers some of your questions...
Author:  mschlott [ Wed Feb 15, 2006 12:58 am ]
Post subject:  Re: prebuffering pause questions
I am supprised that 720x480 will not give a better picture. I have been playing with resolutions and bit rates, trying to get the picture to be as clear as the tuner input. I have not had much luck.

I'm also supprised to find out that myth does not use mplayer. I guess I can quit mucking with the .mplayer/config file. :)


Thanks for the feed back. If 480x480 truely gives me no better picture than 720x480 on my svideo out, I may be able to use wireless yet.
Author:  mschlott [ Wed Feb 15, 2006 8:57 am ]
Post subject: 
Since mplayer is not used, where is buffering done? It must be in memory, becuase I can not find any files on my front end that are being updated.

Previously you had pointed out an extra buffering setting. I assumed this to be the extra audio buffering setting. Does this setting affect video buffering as well? Is there anywhere that the video buffer size can be set as in, increasing the cache setting for mplayer? I may be willing to modify the database directly if that is where it's done.


I'm convinced that I could get rid of this pausing by increasing the buffer size. With a sufficiently large buffer, and a network that is mostly running at speeds above the minimum, there should be no prebuffering pauses. Or am I missing something.

mike
Author:  tjc [ Wed Feb 15, 2006 11:21 pm ]
Post subject: 
mschlott wrote:
Or am I missing something.

The buffer takes a certain amount of time to get enough backlog to bridge an gaps. This is why you see it smooth out after a while. However, everytime you change to a new stream, or change position in the stream you have to flush the buffers and start over...
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