[mythtv-users] What keeps causing "prebuffering pauses" ?!?!?!

Andrew Dodd atd7 at cornell.edu
Fri Jan 30 11:33:09 EST 2004


Quoting Hamish Moffatt <hamish at cloud.net.au>:

> On Wed, Dec 24, 2003 at 06:35:03PM +0100, Robert Krig wrote:
> > Ive read a few posts about this problem in the mailing list. But apparently
> no one has come up with a good explanation or a good solution, or at least I
> havent seen one.
> > 
> > In mythtv 0.12 everything was fine, I've upgraded to mythtv 0.13 and now Im
> getting prebuffering pauses. It doesnt happen all the time, it seems to be
> totally random, but as soon as it starts, I cant get it to stop. Sometimes if
> I switch to a different channel, it will be fine, but if I switch back then
> it starts over again. It doesnt always happen on the same channel either. My
> cpu is only used 40%, my harddisk has more than adequate performance. Im
> pretty sure its not my hardware, since A. Everything was fine in Myth 0.12
> and B. Im not the only one experiencing this. 
> 
> Any resolution for this? I'm getting it sometimes on my DVB-T setup.
> Switch to a particular channel and it occurs non-stop, switch to another
> and it's fine, go back and it starts again. One channel is the most
> affected.
Possible causes:

XvMC and 16bpp are a Bad Combination (Sometimes X config utilities will drop you
into 16bpp without you realizing it.  This happened to me.  I set my box up for
24 bpp default, at some point the default changed to 16, I have NO IDEA how.)

Enable "extra audio buffering" - This helped for me.

Finally, define "more than adequate performance".  Raw read/write speeds are
irrelevant for Live TV, as the HD has to keep seeking back and forth between
locations on the drive.  I had a relatively recent 120GB 7200RPM Maxtor drive
that was *insufficient* for watching Live TV.  (Although other factors were that
it was in an external Firewire case and running a FAT32 filesystem.)  Raw
read/write transfer rate was 20 MB/sec.  It couldn't even handle one LiveTV
stream without occasional prebuffering pauses.  In situations of intense reading
and writing at the same time (example:  Saving the raw video stream from a
recording using avidemux), the transfer rate would drop to below 5 MB/sec due to
the amount of seeking that was being done.

My new Seagate 200GB running ext3 internally works great.  hdparm read tests
approach 60 MB/sec.

Why doesn't someone invent a hard drive with seperate and dedicated read and
write heads???



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