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Nicias Guru
Joined: 06 Dec 2005 Posts: 446
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Posted: Sat May 11, 2013 1:30 pm Post subject: ffmpeg speed/quality/size strange behaviour |
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Hello,
I'm working out transcoding settings for my video collection. Right now it is mostly just uncompressed DVD rips. I decided to look into x264 with ffmpeg. I read this http://ffmpeg.org/trac/ffmpeg/wiki/x264EncodingGuide and did some trial runs with a 5 minute video clip.
If I understand it correctly, I should pick a "crf" value that is of sufficent quality, and then pick a "preset" or speed value that gives me the compression time/file size tradeoff I want. I settled on a crf of 17 (supposedly psychovisually transparent) I put together a script to check the compression time/file size of various speeds and I found something strange: Slower speeds didn't produce better compression, in fact after a point, they produced larger files.
I suppose my question is, am I doing something wrong, or is there just little to no point to the slower compression presets? Perhaps it makes more of a difference with a higher crf?
Test script: Code: | #!/bin/bash
TEMPDIR=/var/tmp/dvd-import/
LOGFILE=speed-log.txt
for x in ultrafast superfast veryfast faster fast medium slow slower veryslow
do
echo "Starting speed=$x-mp3 encoding: " `date` >> ${LOGFILE}
ffmpeg -i input.mkv -c:v libx264 -preset $x -crf 17 -c:a libmp3lame -q:a 0 -ac 2 ${TEMPDIR}$x-17-mp3.mkv
echo "Starting speed=$x-mp3 indexing: " `date` >> ${LOGFILE}
mkvmerge -o $x-17-mp3-index.mkv --engage no_simpleblocks ${TEMPDIR}$x-17-mp3.mkv
echo "Finished speed=$x-mp3: " `date` >> ${LOGFILE}
echo "Filesize: " `ls $x-17-mp3-index.mkv -lh | cut -d" " -f5` >> ${LOGFILE}
echo "Starting speed=$x encoding: " `date` >> ${LOGFILE}
ffmpeg -i input.mkv -c:v libx264 -preset $x -crf 17 -c:a copy ${TEMPDIR}$x-17.mkv
echo "Starting speed=$x indexing: " `date` >> ${LOGFILE}
mkvmerge -o $x-17-index.mkv --engage no_simpleblocks ${TEMPDIR}$x-17.mkv
echo "Finished speed=$x: " `date` >> ${LOGFILE}
echo "Filesize: " `ls $x-17-index.mkv -lh | cut -d" " -f5` >> ${LOGFILE}
done
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Resulting log flie Code: | Starting speed=ultrafast-mp3 encoding: Fri May 10 19:21:45 EDT 2013
Starting speed=ultrafast-mp3 indexing: Fri May 10 19:23:06 EDT 2013
Finished speed=ultrafast-mp3: Fri May 10 19:23:13 EDT 2013
Filesize: 165M
Starting speed=ultrafast encoding: Fri May 10 19:23:13 EDT 2013
Starting speed=ultrafast indexing: Fri May 10 19:24:20 EDT 2013
Finished speed=ultrafast: Fri May 10 19:24:26 EDT 2013
Filesize: 166M
Starting speed=superfast-mp3 encoding: Fri May 10 19:24:26 EDT 2013
Starting speed=superfast-mp3 indexing: Fri May 10 19:26:26 EDT 2013
Finished speed=superfast-mp3: Fri May 10 19:26:31 EDT 2013
Filesize: 109M
Starting speed=superfast encoding: Fri May 10 19:26:31 EDT 2013
Starting speed=superfast indexing: Fri May 10 19:28:19 EDT 2013
Finished speed=superfast: Fri May 10 19:28:23 EDT 2013
Filesize: 110M
Starting speed=veryfast-mp3 encoding: Fri May 10 19:28:23 EDT 2013
Starting speed=veryfast-mp3 indexing: Fri May 10 19:31:01 EDT 2013
Finished speed=veryfast-mp3: Fri May 10 19:31:03 EDT 2013
Filesize: 51M
Starting speed=veryfast encoding: Fri May 10 19:31:03 EDT 2013
Starting speed=veryfast indexing: Fri May 10 19:33:28 EDT 2013
Finished speed=veryfast: Fri May 10 19:33:31 EDT 2013
Filesize: 51M
Starting speed=faster-mp3 encoding: Fri May 10 19:33:31 EDT 2013
Starting speed=faster-mp3 indexing: Fri May 10 19:38:12 EDT 2013
Finished speed=faster-mp3: Fri May 10 19:38:15 EDT 2013
Filesize: 59M
Starting speed=faster encoding: Fri May 10 19:38:15 EDT 2013
Starting speed=faster indexing: Fri May 10 19:42:46 EDT 2013
Finished speed=faster: Fri May 10 19:42:48 EDT 2013
Filesize: 60M
Starting speed=fast-mp3 encoding: Fri May 10 19:42:48 EDT 2013
Starting speed=fast-mp3 indexing: Fri May 10 19:49:31 EDT 2013
Finished speed=fast-mp3: Fri May 10 19:49:33 EDT 2013
Filesize: 63M
Starting speed=fast encoding: Fri May 10 19:49:33 EDT 2013
Starting speed=fast indexing: Fri May 10 19:56:06 EDT 2013
Finished speed=fast: Fri May 10 19:56:08 EDT 2013
Filesize: 64M
Starting speed=medium-mp3 encoding: Fri May 10 19:56:08 EDT 2013
Starting speed=medium-mp3 indexing: Fri May 10 20:04:13 EDT 2013
Finished speed=medium-mp3: Fri May 10 20:04:16 EDT 2013
Filesize: 60M
Starting speed=medium encoding: Fri May 10 20:04:16 EDT 2013
Starting speed=medium indexing: Fri May 10 20:12:10 EDT 2013
Finished speed=medium: Fri May 10 20:12:12 EDT 2013
Filesize: 60M
Starting speed=slow-mp3 encoding: Fri May 10 20:12:12 EDT 2013
Starting speed=slow-mp3 indexing: Fri May 10 20:24:00 EDT 2013
Finished speed=slow-mp3: Fri May 10 20:24:02 EDT 2013
Filesize: 61M
Starting speed=slow encoding: Fri May 10 20:24:02 EDT 2013
Starting speed=slow indexing: Fri May 10 20:35:35 EDT 2013
Finished speed=slow: Fri May 10 20:35:38 EDT 2013
Filesize: 62M
Starting speed=slower-mp3 encoding: Fri May 10 20:35:38 EDT 2013
Starting speed=slower-mp3 indexing: Fri May 10 20:58:29 EDT 2013
Finished speed=slower-mp3: Fri May 10 20:58:31 EDT 2013
Filesize: 60M
Starting speed=slower encoding: Fri May 10 20:58:31 EDT 2013
Starting speed=slower indexing: Fri May 10 21:21:10 EDT 2013
Finished speed=slower: Fri May 10 21:21:12 EDT 2013
Filesize: 60M
Starting speed=veryslow-mp3 encoding: Fri May 10 21:21:12 EDT 2013
Starting speed=veryslow-mp3 indexing: Fri May 10 22:02:05 EDT 2013
Finished speed=veryslow-mp3: Fri May 10 22:02:08 EDT 2013
Filesize: 53M
Starting speed=veryslow encoding: Fri May 10 22:02:08 EDT 2013
Starting speed=veryslow indexing: Fri May 10 22:42:53 EDT 2013
Finished speed=veryslow: Fri May 10 22:42:55 EDT 2013
Filesize: 54M
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Maitreya Guru
Joined: 11 Jan 2006 Posts: 441
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Posted: Wed May 15, 2013 9:03 am Post subject: |
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DVD rips come from DVD's (duh) which at most (as i've seen) have MPEG-2 @ 8Mbit.
I guess the sweet spot for that crf is there because quality of the input is limited? |
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