Removed a warning about comparision between signed and unsigned variable in ffmpeg_decoder.

Signed-off-by: Lukasz Gromanowski <lgromanowski@gmail.com>
Removed a warning about comparision between signed and unsigned variable in ffmpeg_decoder.

Added ifdefs because changes in API were introduced in libavc 56.1
and this code doesn't compile with older versions (ie. on Ubuntu, or Debian)

Signed-off-by: Lukasz Gromanowski <lgromanowski@gmail.com>
Simplified casting when comparing to AV_NOPTS_VALUE.

AV_NOPTS_VALUE is casted to int64_t when compared with pts,
so with libavc >= 56.1 it should be no-op because in that version
it's already signed int.

Signed-off-by: Lukasz Gromanowski <lgromanowski@gmail.com>
Merge remote-tracking branch 'lgro/ffmpeg_decoder'