[mythtv-users] Capture Card Advice

Dennis Cartier pvr at trigger.net
Thu Jul 24 17:11:22 EDT 2003



> I guess my question comes down to is this: obviously, a software
> encoder can
> potentially produce a better image given enough computing power,
> with little
> to no artifact, smearing, or ghosting problems on the encode
> side, and good
> de-interlacing of the source image.  Since the hardware encoders are fixed
> silicon (unless there's a pga in there), are they at a fixed compression
> mode or do they allow different compression levels of the mpeg encoding.

The PVR-250's use a fully programmable compression engine that uses firmware
that you download to the card when you load the drivers. You can select all
aspects of the resulting MPEG2 stream, the size of the captured images, as
well as the bitrate of the stream. Selecting a lower bitrate reduces quality
and also results in much smaller captures. Capturing at DVD quality @ 720 x
480 takes about 4GB per hour on my PVR-250.

The other thing to consider is how to support multiple tuners. Using
PVR-250's I  can use 4 of them simultaeously on two very slow backend
machine. Doing this with POT's (Plain Old Tuners) would require a lot of CPU
power.

Dennis




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