Ryan Steffes wrote:
It seems like every time I feel like I get a good grasp on how the
bitrates and resolutions and codecs play together something comes up
that confuses me. Like just about everyone, I'm trying to get the
best quality for the least space, and I thought I was doing alright.
My WAF doesn't tolerate graininess very well, and blockiness is a
killer. I have a PVR150 that I record at 352x480 3500/ 720x480 5000/
720x480 6000 by quality level. The HQ ones I leave alone, but the
low quality ones I autotranscode to mpeg4 at 352x480 2200 with the
four high quality options turned on. This seems to give good quality,
with a half hour show coming in at around 700MB.
Last night though, I ripped a few dvd's to take with me on a trip this
weekend, and I realized that I was ripping a full 140 minute DVD to
about 1GB with perfectly good quality, at only around 1000 bps VBR.
If I tried to transcode my shows at that, they'd look terrible. I'm
sure I'm missing a basic principle somewhere, but I can't figure out
what it is. I would think changing the format would have something to
do with it, from mpeg2 to mpeg4, but wouldn't that apply to the dvd as
well? Double pass encoding might be part of the answer as well (I
don't think myth can do that, can it?)
Can someone explain this effect to me?
I'm recording all my shows from a satellite receiver at 720x480
(DVD-compatible resolution) at 2200kbps VBR up to 9800kbps with
PVR-x50's. My recordings average about 1.15GiB/hr. Picture quality is
very good on my 27" TV. A friend is using the same settings, but
playing back using a projector (8 1/2 foot TV) and--other than the
artifacts from his analog cable signal--it looks great. When playing
something I recorded on his system, the quality is about the same as a
DVD ripped to a 700MB MPEG-4. See
http://mythtv.info/moin.cgi/UserManual_2fTechnicalDetailsAppendix_2fRecordingParameters
I've found that any type of re-encoding of the signal will either
significantly degrade the quality (graininess/blockiness) or require me
to crank up the bitrate to higher than the original (which is why I
record using DVD-compliant settings...).
Also, input signal quality does make a difference. Analog cable signals
often require greater bitrate than digital cable/satellite (which only
becomes analog for the short trip to the PVR-x50, which isn't long
enough for any noticeable degradation of signal quality).
HTH.
Mike
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