I did extensive tests with 1.9.0-RC3, regarding the average and maximum
bit rate, and the results are intriguing. It seems like the bit rate is
too high.
Source is a cheap new DV camcorder, NTSC 16:9. I've a bunch of DV files
that I transcode with different parameters, the numbers below are the
average and maximum bit rate for each file, as reported by mplex when
multiplexing the video and the audio tracks.
I am transcoding for DVD.
First off, a thoroughly default configuration.
mpeg2enc -v 0 -I 1 -f 8 -b 8000 -F 4 -n n -a 3 -o blah
These are the average and maximum bitrates for the set of files I use as
input. Each line in the table below represents another input file.
avg max
4902000 8682400
4592400 6982000
4612000 8553600
4559600 6766400
4267600 6428000
5892000 9595200
5288000 9306400
8031600 9641200
4768000 9283600
4727600 7980800
Now I'm doing a bunch of tests with more complex parameters. I am trying
to maximize image quality.
The only things that change from one test to another are -q (quality
factor, either 7 or 8), and the matrix (default, kvcd and tmpgenc). A
sample command line picked randomly from one of the tests is:
mpeg2enc -v 0 -I 1 -f 8 -b 8000 -F 4 -n n -a 3 -o
"va-2007.12.09_16-55-18.m2v" -c -q 8 -4 1 -2 1 -s -D 10 -K kvcd -R 2 -M 2
These are the results. The values for -q and -K can be deduced from the
names of the logs printed before each set of results (format is:
va-${q}-${K}-mplex.log). The other parameters do not change. Each line
represents a different file in the set of input files.
va-7-default-mplex.log
avg max
7142800 9865600
6896400 9557600
6978000 10058000
6462800 8055200
6074000 8042400
7407600 9738800
7137200 9618800
8036000 9870400
6469200 9840800
6557600 9621600
va-7-kvcd-mplex.log
avg max
4279200 8897600
4182800 6774000
3966000 7983600
3579600 5184800
3310000 4769200
4769200 9402000
4310400 7422000
7998400 9406400
4151200 7887200
4003200 7381200
va-7-tmpgenc-mplex.log
avg max
4860000 9014000
4679200 7060000
4566800 8618400
4245200 6052000
3957600 5659600
5607600 9658800
5054000 8530400
8032000 9589600
4748400 9254000
4610000 8070000
va-8-default-mplex.log
avg max
4939600 8903600
4678800 7069200
4660400 8322000
4510800 6237200
4299200 6067600
5760800 9594400
5201200 8762000
8031200 9836400
4764800 9136800
4665600 7923200
va-8-kvcd-mplex.log
avg max
3377200 7429600
3338400 5602800
3092400 6458000
2770800 4051600
2549600 3687200
3636800 8965600
3323200 5699600
7469600 9587200
3239600 6257200
3123600 5996000
va-8-tmpgenc-mplex.log
avg max
3670400 7559600
3594000 5654000
3418400 6902800
3166800 4598000
2952800 4272000
4182400 8666400
3801200 6608400
7886000 9236800
3611200 6952400
3488800 6508800
It seems like it's overshooting a bit. E.g., with -q 7 -K default the
max is as high as 10000, even though I'm using -b 8000
The only combination that's remotely acceptable is -q 8 -K tmpgenc, but
even then the third file from the bottom gets up to 9200k bitrate.
I can provide a sample of one of the DV input files, but only by request
and only to the developers - I won't post the URL to the mailing list
because even a short sample can be pretty big.
--
Florin Andrei
http://florin.myip.org/
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