mjpegdec: parse JPS extension and save relevant stereo3d information

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avcodec/mjpegdec Fix potential memleak of stereo3D at the end in case of decoding failure

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avcodec/mjpegdec: use av_freep() instead of av_free()

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
Force automatic thread_count to 1 for cbr mjpeg frame threading.

Constant bit rate mjpeg encoding fails for threads > 1 and frame threading.
Warn the user if mjpeg cbr encoding with frame threading was requested.