flvdec: use the correct audio codec id when parsing metadata
flvdec: read audio sample size and channels metadata

This is needed in order for the FLV demuxer not to detect a codec change when
using the "flv_metadata" option.
Merge commit 'c3d015775388882b8a122afc337ea35108f652be'

* commit 'c3d015775388882b8a122afc337ea35108f652be':
  flvdec: use the correct audio codec id when parsing metadata

Merged-by: Michael Niedermayer <michaelni@gmx.at>
Merge remote-tracking branch 'qatar/master'

* qatar/master:
  flvdec: read audio sample size and channels metadata

Merged-by: Michael Niedermayer <michaelni@gmx.at>
avutil/buffer: add get_opaque

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
ffmpeg/avformat: factor av_guess_frame_rate() out

This will be used in ffplay

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