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How can I concatenate several .webm files (e.g. downloaded from youtube) into a single file? I've tried a simple cat followed by "mencoder -forceidx -oac copy -ovc copy ..." - didn't work. I'm using Linux.

studiohack
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eug
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  • That's gonna be hard – most videos are not meant for concatenating. You can somewhat do this with MPEG-2 and h.264, but no idea for WebM, *unless* you want to re-encode them. – slhck May 06 '12 at 09:39

3 Answers3

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As Lou mentioned, try mkvmerge like this (from command line):

mkvmerge -o output.webm -w file1.webm + file2.webm

Laurent S
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Remember that the WebM container format is a strict subset of Matroska, so Matroska tools will work on WebM files. Try mkvmerge (which ships with mkvtoolnix) to re-mux files without re-encoding. The result may or may not be satisfactory for your purposes, but mkvtoolnix is mature and GPLv2-licensed, and well worth a try. There's even a mkvmerge GUI.

Lou Quillio
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  • Thanks for this info - I think this is definitely on the right track. I've tried the GUI but just feeding the files to it seems to be creating an output with multiple video tracks, not a single video whose length is the sum of all the inputs.. – eug May 09 '12 at 06:38
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    An mkvmerge GUI operation analogous to Laurent S's CLI solution above is to **Add** the first file and to **Append** the subsequent files in the series. Might not be obvious at first. – Lou Quillio Jul 09 '12 at 19:46
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If you use the mkvmerge GUI, you right-click in the "input file" section, then choose "Add Files" and select the first file from wherever you stored it.

Now, you right-click on the first file in the "input file" section and select "append files".

If, instead of choosing "append files", you chose "add files as additional parts", it won't work. This option is for combining files where the second/third/etc files don't have video headers (like if you used the Unix split command to just cut a file into chunks). If you chose that option with two WebM files, you wouldn't get any errors, but only the first video file will be present in the resulting MKV.

Chris Slycord
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