[FFmpeg-user] Modify sequence header in MPEG with no transcoding?
david.griffiths at gmail.com
Thu Jul 27 15:16:37 EEST 2017
Hi, I have some MOD files with incorrect aspect ratio. MOD files are basically MPEG and were produced by Panasonic/JVC camcorders a few years ago. I can import into things like iMove and Elements but they appear in 4:3 format instead of 16:9. The cause is that the MPEG Sequence Headers have aspect ratio incorrectly set to 4:3 (there is a separate MOI file that says the aspect ratio is actually 16:9).
Anyway, lots of people have hit this problem and the solution usually suggested is to use a program called SDCopy which “sets the widescreen flag” (not actually a flag at all it appears). I’m on a Mac so can’t run SDCopy. I haven’t been able to find any alternatives to SDCopy apart from using ffmpeg to re-encode. I’ve experimented with a Hex Editor to change all the sequence headers from the 4:3 value to 16:9 and that works fine so I’m thinking of writing a little program to do this. Not having to re-encode is my goal here.
But before I do so I just want to check that I haven’t missed some obscure ffmpeg feature that will allow me to do this? From what I read it appears you either have to decode and then reencode or there is the copy option, but the copy option doesn’t touch the sequence headers (I tried "ffmpeg -i file.mod -acodec copy -vcodec copy -aspect 16:9 file.mpeg”)
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