Some questions about bitrate

[Fangrf]

What is the relationship between the sample rate in gnuradio and the bitrate in ffmpeg? The bitrate should be set to how much? I found the delay between transmit and receive is more than 10 seconds. I think may there may be a rate mismatch that causes some data to be buffered. And I didn't use udp source, because I found that udp source may be dropped out. I use file source,and I used fifo file.