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  1. Hello guys, I have a question, there is a way to change the audio from an MP4 video file wich is 5.1 to stereo avoiding to encode all the video?
    I allready use this : ffmpeg -i file.mp4 -acodec mp3 fileout.mp4 but it takes about 30 minutes, I just wanna change the audio since my player does not support 5.1 channel.

    Is there any way to do it faster? I have to encode about 35 files.

    Thanks in advance
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  2. By default ffmpeg re-encodes the video. So you have to tell ffmpeg not to via -c:v copy:
    ffmpeg -i "file.mp4" -map 0 -c:v copy -c:a aac -ac 2 "fileout.mp4"
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  3. Thank you sneaker, Now I'm facing another problem, I have some files in .mkv, any way to do the same? change the audio 5.1 to stereo without reencoding or the fastest way?
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  4. It works the same way. Just change the filenames to xxxx.mkv instead of xxxx.mp4.
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  5. my mistake was that input on mkv output on mp4 then show an error about vcodec, now input mkv output mkv works flawless, thank you again sneaker!
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  6. I have another problem with MKV files, 3 of my files have captions(like subtitles) with corporative information on video startup, this "subtitles" are gone, the mkv now is on stereo audio, but there is no subtitles, any way to the new file in stereo audio also includes the "subtitles" ?
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  7. Try to also add -c:s copy
    If it doesn't work show your complete command-line and ffmpeg log.
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  8. aBigMeanie aedipuss's Avatar
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    if all you want is the old subs in the new mkv then start mkvtoolnix, drag the new mkv into source files window, then drag the old mkv in. in the lower window uncheck the video and audio associated with the old video, and anything else that shows up you don't want in the new video. give the vid a new name and start muxing.
    "a lot of people are better dead" - prisoner KSC2-303
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