Hi!
Yesterday I was experimenting with creating a CVD and wondering what
effect the various new options in mpeg2enc would have when making
a CVD.
The results were amazing. For casual viewing (and depending on the
data source) it appears that over 60 minutes of video can be placed
on a 700MB (well, ~800 when the mode2form2 sectors are taken into
account) CD-R!
First the standard SVCD case. I'm in NTSC-land so the encoded frame
size is 480x480. Using the base command:
mpeg2enc -f 4 -q 8 -K kvcd -E -8 -4 2 -2 1
the 12962 frames encoded with an average bitrate of 2232 kb/s (according
to mplex).
Then "yuvmedianfilter -t 0" was added to the pipeline. This filters
only the chroma which helps reduce the dark scene pixelation (the
splotches/blocks that appear in dark scenes). The average bitrate
went down slightly to 2206 kb/s. Small effect to be sure on the
average bitrate but in the realm of ~2000kbs even a 1 or 2% change
is desireable (and the picture quality improved slightly).
Next the "-R 0" (omit B frames) option was added to the encoder so
the command became:
mpeg2enc -f 4 -q 8 -K kvcd -E -8 -R 0 -4 2 -2 1
the average bitrate went down to 1990 kb/s - a signficant drop!
Finally a mild denoising step was added in the form of the
'yuvdenoise -S 0 -l 1' command. The average bitrate dropped to
1572 kb/s. A very signficant drop!
So the standard SVCD results look like this:
base 2232
base+median 2206
base+median+R0 1990
base+median+R0+denoise 1572
For CVD creation I used y4mscaler and told it to crop 8 pixels from
each side (of a 720x480 frame) and then perform a 2->1 scaling
from 704x480 to 352x480. A CVD preset is on y4mscaler's TODO list
I hear ;)
The results for CVD encodings using the same commands as above:
base 1708
base+median 1661
base+median+R0 1439
base+median+R0+denoise 1220
Using vcdimager and cdrdao to burn a CD-R resulted in a disc that
played fine in both my portable (Audiovox) DVD player and of course
in the Philips 724. Quality of image was noticeably lacking compared
to the DVD encoding but that was to be expected. The portable
player's LCD screen looked a lot better than my older TV set.
For playback on portables or a computer the CVD format looks fine but
for extended or critical viewing on a TV set the limitations of the
CVD/SVCD format are noticeable (less detail and so on).
At ~1200 to 1500 kb/s getting almost 70 minutes of video on a
10cent (if that much ;)) CD-R looks to be within reach.
Of course one could also create a VBR VCD at 352x240 and get even
more play time ;)
Cheers,
Steven Schultz
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