[mythtv-users] pvr250 vs standard bttv sanity check

[Richard Lee-Morlang]

Hi people,

In searching through the archives for info, I started questioning some
assumptions, so I'm hoping some people can chime in with their own
experience.

My current box is an XP2200 with a WinTV Stereo card. I believe I record
at Mpeg4 2200 by default. For the most part, it works well, but I have
three annoyances, starting from the least annoying:

* blocking artifacts, particularly in darker scenes. This is probably
mostly to do with my current settings where I'm recording too dark and
playing back too bright, bringing a good portion of the blacks up into
the dark grey range and therefore causing nasty blocking. At least,
that's my theory.
* a fairly consistent stutter visible once or twice a second, mostly
only noticeable in panning scenes. Hockey is completely unwatchable for
me as a result, but everything else is mostly tolerable. I've tried a
few things to reduce this but to no (positive) effect.
* I can't reboot the box or do anything CPU intensive on it without
first checking to see if I have a suitable hole in my recording
schedule.

My proposed solution is to get a PVR-250 and stick it in my fileserver.
I'm expecting the PVR-250's hardware encoder to eliminate the stutter
and mostly eliminate my CPU concerns, and having the backend running on
a separate machine eliminates my reboot issues. At least, that's the
theory. Anyone disagree so far? :-)

Of course, encoding in MPEG2 is going to take up more space than my
current MPEG4 settings, so I'd planned to set the default MPEG2 bitrate
to something fairly high and transcode back down to ~2200 MPEG4.
Opinions about whether this is a good idea seem to be all over the map,
however, with some people convinced it's a Really Bad Idea.

It seems like a lot of the naysayers were a bit confused about the
function of bitrate, and were saying that converting a MPEG2 2200 to an
MPEG4 2200 (or something along those lines) made things look worse. But
it seemed like some people were quite convinced that converting from a
high bitrate MPEG2 to a low bitrate MPEG4 really did make things look a
lot worse, which is not what I'd expect.

I do realize that ANY transcoding results in some loss of quality. I
also realize that I've seen ~900 - ~1500 Kbps DivX's that were ripped
from DVDs that looked entirely acceptable to me, and far superior to
anything I've ever seen from VHS or cable. (Well, I've seen ~450Kbps
MPEG2's that were superior to some cable signals, but that's another
topic altogether. :-)

I also realize that an MPEG4 should look better than an MPEG2 at the
same bitrate. I'm only trying to determine whether transcoding a
~8000Kbps MPEG2 to a ~2200Kbps MPEG4 will result in something of
approximately similar quality while saving diskspace.

Bits of wisdom regarding variable bitrates, multipass encoding, a/v sync
issues, etc.. are also most welcome.

Rick