Taking into account you use PASS, TVH will 'take banana .. give banana' so someone else is generating the actual encoding (H264 or H265 ... or whatever). 'Someone else' is the one that decide the bitrate (and the variability in bitrate).
To add even more variability ... if you use YouTube (or some internet source), the networks tends to add variability in fluency of the packets. To give you an example: even when you select constant bitrate the encoding (amount of bits allocated per second) are constant, but when you look at the internet bandwidth on your router you will see in average is the constant bitrate but is bouncing up/down due to internet latency. Longer the distance ... more variability you are going to see (because more servers with more constrains are going to be added on your path from source to destination).
An interesting feature for TVH would be to add a variable buffer ... like sling box implementation.
Description of the feature:
- when you switch channel the buffer is short (in order to start playing at destination with small delay)
- reduce temporary the frame rate in playback in order to generate a buffer increase at the destination.
- when buffer is long enough you switch to source frame rate.
- I don't know if TVH can override the Time to Play ( I think is called) on the stream in order to force client (like Kodi) to change actual frame rate played (and force him to increase the buffer).