[mythtv-users] Video Quality

Steve Briggs zzybaloobah at yahoo.com
Sat Jan 28 05:21:00 UTC 2006


The URL,
http://www.mediachance.com/dvdlab/tutorial/bitrate.html
is fascinating!

My baseline is that I'm used to watching VHS tapes in EP mode.
(OK.. I'm showing my age -- I grew up watching fuzzy OTA from
an outdoor mast VHF/UHF antenna.)

I record analog SD as MPEG-4 at 432x480, 2 Mbps.  If I take that
chart and assume that MPEG-4 needs half the bitrate of MPEG-2 
(for the same quality) and that bitrate scales linearly with
frame size, I get the following bitrates
   For LP quality 2.7 Mbps / 2 * 432 / 352 = 1.7 Mbps
   For SP quality 2.9 Mbps / 2 * 432 / 352 = 1.8 Mbps
   For XP (?) quality 3.8 Mbps / 2 * 432 / 352 = 2.3 Mbps
All of this is assuming CBR.  I *assume* MPEG-4 is VBR, so
I'm probably in good shape (I *assume* when you provide at
bitrate, that's the average).  Of course, the VHS tapes 
are SIF at 352x240, I'm at least getting 432x480.  

OTOH, I do see artifacts (blockiness) in dark areas.
But, my criteria all along was to keep it under 1 GB/hr.
I record a *lot* of stuff.

Steve


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