# How can I remux FLV movies from YouTube (e.g. into MKV)?

For some obscure reason, I have some video files I downloaded from YouTube as FLV rather than in another format. I would like to re-mux them into, say, MKV (Matroska). When trying to use ffmpeg, I get a Unsupported video codec (7) message. What should I do?

I'd like to be able to do this both in a command-line tool and through a GUI but either is fine.

My OS for the purpose of discussion is Windows XP SP3.

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What's your OS? I was able to do this on CentOS but I had to build my copy of FFMPEG to get support for codecs like these. –  ethrbunny Feb 25 '13 at 22:08
Please show what exactly you tried with FFmpeg and include the full, uncut command line output. Without that it's hard to guess what the problem is. –  slhck Feb 26 '13 at 3:57
FLV is a video codec and MKV a video container, please specify the video codec you want to convert FLV to. –  Peter Feb 26 '13 at 13:27
@Peter: FLV is not a video codec, it's a container. –  einpoklum Feb 26 '13 at 13:30
The codecs don't matter—FFmpeg can just copy them. ffmpeg -i in.flv -c copy out.mkv for example. What happens when you try that? Or, what was the command you tried before, including the full output? –  slhck Feb 26 '13 at 17:56

2. Run X:\path\to\ffmpeg.exe -i input_file.flv -c copy output_file.mkv