[FFmpeg-user] formula for transcoding to ogv, shrinking an mkv

[James Miller]

Attempting to implement Carl's suggestions, I tried this as a first pass: 
ffmpeg -y -i infile.mkv -pass 1 -acodec libvorbis -ab 48k -ac 2 -vcodec 
libtheora -b 100k -threads 0 outfile.ogv and got the following output:

ffmpeg version 0.8.4-4:0.8.4-0ubuntu0.12.04.1, Copyright (c) 2000-2012 the 
Libav developers
   built on Nov  6 2012 16:50:25 with gcc 4.6.3
*** THIS PROGRAM IS DEPRECATED ***
This program is only provided for compatibility and will be removed in a 
future release. Please use avconv instead.
[matroska,webm @ 0x92b9220] Estimating duration from bitrate, this may be 
inaccurate
Input #0, matroska,webm, from 'infile.mkv':
   Metadata:
     ENCODER         : Lavf54.29.104
   Duration: 00:48:52.19, start: 0.000000, bitrate: N/A
     Stream #0.0: Video: h264 (High 4:4:4 Predictive), yuv444p, 830x615, 
PAR 1:1 DAR 166:123, 15 fps, 15 tbr, 1k tbn, 30 tbc (default)
     Stream #0.1: Audio: pcm_s16le, 48000 Hz, 2 channels, s16, 1536 kb/s 
(default)
[buffer @ 0x9375480] w:830 h:615 pixfmt:yuv444p
Output #0, ogg, to 'outfile.ogv':
   Metadata:
     encoder         : Lavf53.21.0
     Stream #0.0: Video: libtheora, yuv444p, 830x615 [PAR 1:1 DAR 166:123], 
q=2-31, pass 1, 100 kb/s, 15 tbn, 15 tbc (default)
     Stream #0.1: Audio: libvorbis, 48000 Hz, 2 channels, s16, 100 kb/s 
(default)
Stream mapping:
   Stream #0.0 -> #0.0
   Stream #0.1 -> #0.1
Press ctrl-c to stop encoding
[matroska,webm @ 0x92b9220] Read error0kB time=2249.50 bitrate= 
0.0kbits/s
frame=33750 fps= 12 q=0.0 Lsize=   36317kB time=2249.99 bitrate= 
132.2kbits/s
video:0kB audio:35611kB global headers:7kB muxing overhead 1.961715%

Then I did a second pass with the following command: ffmpeg -y -i 
infile.mkv -pass 2 -acodec libvorbis -ab 48k -ac 2 -vcodec libtheora -b 
100k -threads 0 outfile.ogv . That resulted in the following output:

ffmpeg version 0.8.4-4:0.8.4-0ubuntu0.12.04.1, Copyright (c) 2000-2012 the 
Libav developers
   built on Nov  6 2012 16:50:25 with gcc 4.6.3
*** THIS PROGRAM IS DEPRECATED ***
This program is only provided for compatibility and will be removed in a 
future release. Please use avconv instead.
[matroska,webm @ 0x9440220] Estimating duration from bitrate, this may be 
inaccurate
Input #0, matroska,webm, from 'infile.mkv':
   Metadata:
     ENCODER         : Lavf54.29.104
   Duration: 00:48:52.19, start: 0.000000, bitrate: N/A
     Stream #0.0: Video: h264 (High 4:4:4 Predictive), yuv444p, 830x615, 
PAR 1:1 DAR 166:123, 15 fps, 15 tbr, 1k tbn, 30 tbc (default)
     Stream #0.1: Audio: pcm_s16le, 48000 Hz, 2 channels, s16, 1536 kb/s 
(default)
[buffer @ 0x94fc480] w:830 h:615 pixfmt:yuv444p
Output #0, ogg, to 'outfile.ogv':
   Metadata:
     encoder         : Lavf53.21.0
     Stream #0.0: Video: libtheora, yuv444p, 830x615 [PAR 1:1 DAR 166:123], 
q=2-31, pass 2, 100 kb/s, 15 tbn, 15 tbc (default)
     Stream #0.1: Audio: libvorbis, 48000 Hz, 2 channels, s16, 100 kb/s 
(default)
Stream mapping:
   Stream #0.0 -> #0.0
   Stream #0.1 -> #0.1
Press ctrl-c to stop encoding
[matroska,webm @ 0x9440220] Read error7kB time=2249.67 bitrate= 
301.6kbits/s
frame=33750 fps= 12 q=0.0 Lsize=   82870kB time=2249.67 bitrate= 
301.8kbits/s
video:46159kB audio:35611kB global headers:7kB muxing overhead 1.336090%

The lossless infile.mkv is 491 MB in size, while outfile.ogv winds up 
being 81 MB. That outfile, for some reason, is slightly larger than the 
file I produced using the 1 pass encoding with the errant -crf option and 
no -b option set: that outfile.ogv came in at 73 MB (command line ffmpeg 
-i infile.mkv -r 13 -acodec libvorbis -ab 48k -ac 2 -vcodec libtheora 
-preset slow -wpredp 0 -crf 22 -threads 0 outfile.ogv). I can't detect any 
difference in quality between the two files: both are of acceptable 
quality for my uses.

Any further suggestions on things to try or corrections to implement?

Thanks,
James