container == RIFF_FOURCC('R','F','6','4'));
TRY_IO(pcm_read32le(&reader->io, &fcc));
ENSURE(fcc == RIFF_FOURCC('W','A','V','E'));
container == RIFF_FOURCC('R','F','6','4'));
TRY_IO(pcm_read32le(&reader->io, &fcc));
ENSURE(fcc == RIFF_FOURCC('W','A','V','E'));