[mythtv] Separate Record and Play boxes? (system design)

Grant Taylor mythtv-dev@snowman.net
Thu, 19 Sep 2002 11:13:58 -0400


>>>>> mythtv-dev@snowman.net writes:

>> I dunno if NFS will be workable for this.  It may add enough jitter
>> that some sort of additional buffering logic will be needed in the
>> player.

> I'm currently using NFS to store all of my movies, and playing them back 
> (with mplayer) without any sort of problems.

> I routinely set the cache in mplayer to 4096KB, just to be on the safe 
> side, but even if I forget to do this, there is not jitter apparent in 
> the output.

Well, this is interesting.  DVD rate is circa 1.5Mbps, IIRC; rtjpeg
tends to produce more data.  But I bet it still fits, certainly so if
mpeg4 is used.

What I wonder about is this buffering - mythtv uses a "ringbuffer"
structure which doesn't appear to implement very much buffering.  And
the primary difference between my system (which jitters excessively)
and Isaac's (which generally doesn't jitter) appears to be disk speed
(5400 vs 7200) and some marginal memory settings on his part.  This
suggests that mythtv may be more susceptible to filesystem
irregularity than mplayer (which works fine for me every which way,
too).

Issac, could you describe how the coder and decoder threads interact
with the files?  It appears that they coordinate through the
RingBuffer class, but that the file reads and writes actually happen
in the coder/decoder threads themselves?

--
Grant Taylor - gtaylor@picante.com - http://www.picante.com/~gtaylor/
    Linux Printing Website and HOWTO:  http://www.linuxprinting.org/