On 11 Nov 2003, Florin Andrei wrote:
> What is _your_ source?
Which one? ;)
The author of mpeg2enc is one. Another can be found in one of
the links from http://www.mir.com/DMG/, go to the MPEG FAQ
and read http://tns-www.lcs.mit.edu/manuals/mpeg2/FAQ
Question/answers #16, #19, #20 and #24.5
In particular #16 which gives the definitions of the MPEG profiles,
note that the "Simple" profile is I and P frame only. One could
look up the formal definitions in one of Charles Poynton's books
but for now the FAQ will suffice ;)
The discussion in #19 and #20 is quite interesting - in essence
at higher (relative to MPEG-1 SIF size) bitrates B frames are
considered by some to be 'wasted bits'.
Then in #24.5 there's the Dual Prime prediction discussed. That's
the part that Ogle doesn't implement but it is most certainly
a part of the standard.
> Mine is a recent el-cheapo Sony digital camcorder (DCR TRV240); kinda
> good in full daylight, but rather noisy in indoors scenes. Is that less
> than perfect enough to warrant dropping the B-frames?
Same here - actually mine's the TRV140 (or was it the 120) - D8 so it's
not analog but nothing fancy (that's for sure :)). Thinking of
getting one of those 3CCD units (Panasonic has one that can be had
for under $1k) one of these days.
Anyhow I shot some footage of the fires that were going on in
Southern California a short time ago (just a couple miles from
the house) and got somewhere around 10% or so reduction in the
bitrate by dropping B frames. I've some tapes made earlier
that I could re-capture and experiment with.
It's also possible to split the difference - instead of dropping
B frames completely you can specify that just 1 is to be used between
P frames. The "-R 1" will reduce but not eliminate the B frames.
It's been mentioned to me that high motion scenes can also benefit
from reducing or eliminating the B frames. Something to consider
when going for maximum quality with live footage.
Cheers,
Steven Schultz
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