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ripping audio from AV files, to avoid transcoding of audio data
post Jan 3 2012, 00:10
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It's been a while since I was last here. Got a quick question.
I've downloaded some video files, that I checked to have an AAC 256KBPS audio part. Let's say I don't want the video part, I want the audio. There are programs which can convert these video files to audio files, but they decode the audio to wav and then convert that to something else. So they transcode the audio. Since 256 k is pretty high quality anyway, I doubt transcoding to something equally high wouldn't make much difference, but still I don't want to lose anything by just taking the video out. Is there a way to cut the video out of the original file?
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post Jan 3 2012, 21:45
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You can do this easy and fast from the command line using mencoder.exe.


I have a video file named input.flv, and I want to extract the raw audio stream to a file named output (at the moment I don't know the file extension).

put mencoder.exe and input.flv in the same folder, and run this command line:
mencoder -of rawaudio -ovc copy -oac copy -o output input.flv

a file named output is created in the same folder.

Don't close the console window yet ...look at the text. You should see something like this:
C:\TEST=====> mencoder -of rawaudio -ovc copy -oac copy -o output input.flv

MEncoder Sherpya-MT-SVN-r32198-4.2.5 © 2000-2010 MPlayer Team
SSE2 supported but disabled
158 audio & 346 video codecs
success: format: 0 data: 0x0 - 0xebb6d
libavformat file format detected.
[flv @ 02230050] Estimating duration from bitrate, this may be inaccurate
[lavf] stream 0: video (flv), -vid 0
[lavf] stream 1: audio (mp3), -aid 0
VIDEO: [FLV1] 320x256 0bpp 25.000 fps 322.7 kbps (39.4 kbyte/s)
[V] filefmt:44 fourcc:0x31564C46 size:320x256 fps:25.000 ftime:=0.0400
Ignoring video stream!
videocodec: framecopy (320x256 0bpp fourcc=31564c46)
audiocodec: framecopy (format=55 chans=1 rate=22050 bits=16 B/s=1000 sample-0)
Pos: 0.9s 22f ( 3%) 0.00fps Trem: 0min 0mb A-V:0.084 [0:55]

Skipping frame!
Pos: 1.2s 32f ( 6%) 0.00fps Trem: 0min 0mb A-V:0.084 [138:55]

Skipping frame!
Pos: 1.7s 44f ( 6%) 0.00fps Trem: 0min 0mb A-V:0.084 [104:55]

Skipping frame!
Pos: 2.7s 71f (10%) 0.00fps Trem: 0min 0mb A-V:0.080 [152:56]

Skipping frame!
Pos: 24.3s 612f (100%) 0.00fps Trem: 0min 0mb A-V:0.049 [250:57]

Video stream: 250.106 kbit/s (31263 B/s) size: 760322 bytes 24.320 secs 612

Audio stream: 57.752 kbit/s (7219 B/s) size: 177075 bytes 24.529 secs


So there is our filetype in red; it is an MP3 file ====>output.mp3
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