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Old 02-02-2011, 02:26 AM   #1
sumeet inani
Registered: Oct 2008
Posts: 902
Blog Entries: 26

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extract audio from video file using mencoder

I ran
mencoder The.Negotiator.mkv -of rawaudio -oac mp3lame -ovc copy  -o sound-mencoder.mp3
I got a 195.3MB mp3 file

ffmpeg -i The.Negotiator.mkv sound.mp3
I get 64.9MB file.

If I analyse both file i see
file sound-*
sound-ffmpeg.mp3: Audio file with ID3 version 2.4.0, contains: MPEG ADTS, layer III, v1,  64 kbps, 48 kHz, JntStereo
sound-menc.mp3:   MPEG ADTS, layer III, v1,  32 kbps, 48 kHz, JntStereo
How can I get smaller audio file using mncoder ?

Last edited by sumeet inani; 02-02-2011 at 02:27 AM.
Old 02-02-2011, 02:41 AM   #2
sumeet inani
Registered: Oct 2008
Posts: 902
Blog Entries: 26

Original Poster
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I have tried
mencoder input.mkv -dumpaudio -dumpfile sound.mp3
Then I read in man page "dumpaudio works for MPEG/AC3 only"

I also found this formula to calculate video bitrate for making dvdrip
bitrate(in Kb/s) = (target_size_in_Mbytes - sound_size_in_Mbytes) * 1024 * 1024 / length_in_secs * 8 / 1000
I found that
sound_size should be obtained from mencoder result that is 195MB not mp3 which is compressed.
How can I get smaller audio file from video using mencoder ?

Last edited by sumeet inani; 03-06-2011 at 11:19 PM.
Old 03-29-2011, 09:03 AM   #3
Registered: Jan 2011
Posts: 83

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You can experiment with bitrate values to ffmpeg with the -ab switcn

ffmpeg -i The.Negotiator.mkv -ab 96k sound.mp3

The lower the bitrate, the lower the file size will be, but audio quality becomes degraded.

Lower bitrates are good for audio that is talk.
Higher bitrates over 128k is best for music.

Another option is use the -fs switch, a file size limit. you choose how big you want the file to be. The example below will create a 5MB file.

ffmpeg -i The.Negotiator.mkv -fs 5000000 sound.mp3

Last edited by RedNeck-LQ; 03-29-2011 at 09:17 AM.


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