Since libavcodec56 libav native opus decoder is used instead of libopus
decoder.
This decoder only ouput float planar audio data (AV_SAMPLE_FMT_FLTP)
This commit detect the output format and convert it to signed 16bits
in case of float planar.

Refs #64245

Change-Id: Idb8240a1158a0add446d7df3b4a1ed51089e2781