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I have three flv files around 30 Mb each. I joined them together using mencoder on Linux with

mencoder -forceidx -ovc copy -oac pcm -o output.flv input1.flv input2.flv input3.flv

The video codec is H.264 and the audio is MPEG-4 AAC.

The resulting file is 390Mb.

Is there a way to join flv files on Linux without this file size increase?

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The reason for the increase is that you are converting the audio to uncompressed PCM: -oac pcm.

Try this instead:

mencoder -forceidx -ovc copy -oac copy -o output.flv input1.flv input2.flv input3.flv
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  • I already tried it but got this error: Audio format 0x4134504d is incompatible with '-oac copy', please try '-oac pcm' instead or use '-fafmttag' to override it. – To Do Feb 14 '14 at 17:40
  • Well, the pcm command is the reason it is increasing in size. Have you tried the other alternative it suggested? – Shevek Feb 14 '14 at 17:52
  • I tried adding the option but got an error message: The fafmttag option must be an integer: -o. I got partial succes with -oac mp3lame: the file size went down to 127 Mb, still bigger than the original, though. – To Do Feb 14 '14 at 17:56
  • Try ` -fafmttag 0x706D ` – Shevek Feb 14 '14 at 20:03
  • Tried that. It tells me that -oac copy can only be done when the different files have the same codec. According to the details of the 3 files they do have the same audio codec. – To Do Feb 14 '14 at 21:42
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I progressively discovered what the problem was.

using the -oac pcm option was rencoding the audio without compression.

It was not possible to use -oac copy -fafmttag 0x706D due to slight differences in the audio bit rate.

Using -oac mp3lame reduced the file size but a bit rate higher than the original was being used.

Using -oac mp3lame -lameopts vbr=3:br=96 I got a file with a size equivalent to the sum of the three original files. I did not check if the sound quality is the same or not.

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  • 1
    That is what my next suggestion would have been ;) – Shevek Feb 19 '14 at 12:13

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