Hello,
My main question isn't specifically for mjpegtools, but I think
it's of interest to this group, and also I think I'm more likely
to get a good answer here. It's about the values I'm seeing from
the dvdview program recommended here a few days ago -- and since
it seems development on dvdview stopped over a year ago, I'm
further inclined to ask here.
And the question basically is what some of the numbers mean that
are reported for each "SequenceHeader" (as reported with the "-v 1"
setting. Most of the numbers are easily understood. The
strangest one though is the one I'm most interested in: "bitrate".
Based on the values I used to encode the mpeg2 files I've been
testing with "dvdview", it seems that the reported value of bitrate
is always 2.5 times the value I encoded at. So if I set the
max bitrate at 10000, the reported value is 25000. Which means,
I can easily figure out the actual value, but I'm still very
curious as to why the number is multiplied.
But I'm more curious about why the number never changes (so now this
is an mjpegtools question). I generally run "mpeg2enc" something
like:
% mpeg2enc -S 400 -B 384 -q 4 -b 8000 -f 8 -r 16 -N -I 1 -v 0 -o
iyis_vid.m2v < iyis_vid_dn.yuv
So, why if I'm doing variable bitrate encoding, does the bitrate
never change?
NOTE: these were from encodings done with version 1.6.1 of mjpegtools.
Another question that occured to me concerns the -B option: in
the above senario, would the video stream I'm encoding use up
to 8000kbs, or would it actually just use (8000-384)kbps? So,
if I were to set the max bitrate at 10000, would using the -B
option preserve space for other streams? Or do I also need to
make sure to subtract other stream usage from the 10000 to
stay within the DVD spec?
And, I'd also like to know what some of the other values reported
with each SequenceHeader are:
VBV buf.size -- generally reported as 112, except from
an mpeg-1 trailer I downloaded, which reported 3.
aspect code -- always seems to be 2 for mpeg2enc output
(including an SVCD), and 1 for an mpeg-1 file
I have.
constrained -- no idea. It was always false except the
mpeg-1 trailer.
profile -- don't know, but possible values are: Simple,
Main, SNR, Spatial and High.
level -- don't know, but possible values are: Low, Main,
High and High1440.
As an aside, I did try to modify dvdview to show the "bitrate"
value on screen, but didn't find an existing means by which to
get that value to the part of the code that does to video post
processing, so figured I'd just watch the text on the terminal
for now.
Thanks once again,
Bill
--
Bill Sherman
VR Impresario & co-author "Understanding Virtual Reality"
NCSA Virtual Environments Group
[EMAIL PROTECTED]
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