Provides a way to change bandwidth parameter inside DASH manifest after a non-CBR H.264 encoding.
Caller now is able to compute the bitrate by itself, after all packets have been written, and then set that value in AVFormatContext->streams->codecpar->bit_rate before calling av_write_trailer. As a result that value will be set in DASH manifest.
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>