avformat/rawdec: add FF_DEF_RAWVIDEO_DEMUXER2, which allows specifying the flags

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avformat/rawdec: mark raw vc1 and mjpeg as having no timestamps

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avformat/utils: dont wait for a first dts on demuxers which have AVFMT_NOTIMESTAMPS set

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avformat/rawdec: Increase probe score when "Content-Type: image/jpeg" is found at the file start

Based-on code by: Carl Eugen Hoyos and Andrey Utkin
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>