avformat/mpeg: do not count PES packets inside PES packets during probing

Fixes: misdetection of test2.mp3

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avformat/mpeg: add commented out av_log() to probe

This is commonly needed for debugging mis-detections

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avcodec/utils: check AVframe.format being set in avcodec_encode_video2()

We dont fail hard if its not set as the old API allowed this and our examples
did in the distant past not set it, these examples still work with the
current code and some encoders.

Based on suggestion by: funman
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>