FFMPEG does not support J2C output

[Pierre-Anthony Lemieux]

ffmpeg -i blah.mj2 -frames:v 1 -vcodec copy -y blah.j2c results in a mjp2 file (starts with 0000000c6a5020200d0a870a) instead of a file that contains a bare codestream (starts with FF4F).

[Balling]

Erm, with mer_shrt_23976_vdm_sdr_rec709_g24_3840x2160_20170913_12bit_DCDM.4bpp.mxf file it produces the magic MIME FF4FFF5100, as it should.

[Balling]

Oh, can be reproduced with ​https://samples.ffmpeg.org/ffmpeg-bugs/trac/ticket4471/spot-day.mj2

[Pierre-Anthony Lemieux]

Yes, this is because MXF wraps J2Cs :)

[Pierre-Anthony Lemieux]

The fundamental issue AFAIK is that FFMPEG treats MJ2, JP2 and J2C as the same format, which they are not. This is not a problem on input, because the J2K parser accepts all of them. It is a problem on output when copying the codestream since a MJ2 is not the same as a J2C file.