mlpdec: support major sync headers with optional extension blocks

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
mlpdec: support TrueHD streams with an Atmos substream

The fourth substream is being discarded, since its not raw audio data,
but an encoded Atmos stream which needs a specialized decoder.

Fixes decoding of the true hd stream from Transformers\ -\ Age\ of\ Extinction\ 2014\ 1080P-003.mkv

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avformat/mp3dec: avoid early EOF with concatenated gapless mp3s

Consider a file created with something like:

    cat file1.mp3 file2.mp3 > result.mp3

Then if file2.mp3 has gapless information, result.mp3 would stop playing
something in the middle. This happens because the gapless info directs
the decoder to discard all samples after a certain position. To make
matters worse, the gapless info of file2.mp3 will be used when playing
the file1.mp3 part, because the gapless info is located at the end of
the file.

While handling concatenated gapless files correctly would be insane and
a lot of effort (especially without scanning the whole file on opening),
it's easy to prevent at least early EOF. Playback will happen to work,
even if it's slightly broken.

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
rtpdec_hevc: do not print an error message if the received packet has a valid header but lacks additional bytes as payload

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>