forMultistreamBitRate
s = MediaString::forMultistreamBitRate(format.u.multistream.avg_bit_rate,
s = MediaString::forMultistreamBitRate(format.u.multistream.avg_bit_rate,
s << (empty ? "" : ", ") << forMultistreamBitRate(format.avg_bit_rate,
static BString forMultistreamBitRate(