Add stereo rematrixing support to the AC-3 encoders.

[ffmpeg] / tests / ref / acodec / wmav1

26a7f6b0f0b7181df8df3fa589f6bf81 *./tests/data/acodec/wmav1.asf
106004 ./tests/data/acodec/wmav1.asf
stddev:12245.52 PSNR: 14.57 MAXDIFF:65521 bytes:  1064960/  1058400
stddev: 2095.89 PSNR: 29.90 MAXDIFF:27658 bytes:  1056768/  1058400