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I am using GNU/Linux(Arch Linux), and i need to transcode some videos from .avi/.mov to .webm.

I don't have the original file for most videos, only the "very compressed" .avi, and i can't loose any quality (i will replace the older video, with the transcode). How can i do it?

I already tried ffmpeg (with "ffmpeg -i file.avi file.webm", but it reduces quality) and VLC (the video goes perfect, but the audio goes out of sync (I have "synchronize on audio track" on, but there is no improvement).)

I also tried many other programs like "Transmaggedon", "Arista", "Sinthgunt", "winFF" and "Handbrake" without good results(or results at all).

Thanks for your support

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$> ffmpeg -i in.avi -c:v copy out.mkv

note: .webm is essentially a matroska (.mkv) container with vp8 video and vorbis audio. so, technically you can only create a webm if your source-media is the same as vp8 video and vorbis audio .. which in your case is not the case, i guess. on the other hand: the matroska container eats it all, thus the example yielding a .mkv

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Note that the output is valid VP8 only if your source files already contain VP8 video and any audio is Vorbis. ffmpeg has no problem with other formats, but browsers won't accept them since VP8 mandates those stream formats. – Mechanical snail Aug 16 '12 at 5:48
Mostly they are encoded with MPEG-4 and MPGA I also need to use some of the files in <video> tags(HTML) and they should be .webm in my case. (bandwidth is not a problem(lan-only)) – Cláudio Pereira Aug 16 '12 at 5:51
@Claudiop: that is why i put the "note" there. you won't be able to create a "lossless" .webm if you won't have vp8 video and vorbis audio. end of story. you can throw a lot of bits to the reencoder and hope for the best, but you have to reencode it to be a valid .webm. – akira Aug 16 '12 at 5:57
@akira So if i change the "lossless" with "loss as less as possible"? VLC made a perfect "re-encode" with a good size, the only problem was the audio(out-of-sync). Is there any way to make the same with ffmpeg(but with everything in sync)? – Cláudio Pereira Aug 16 '12 at 6:00
@Claudiop: what is your question? the ffmpeg-commandline with as much bitrate as possible to get the best looking .webm? – akira Aug 17 '12 at 12:39

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