Max Bitrate transcode issue

[BillOatman 596]

Hi.  Windows server stable release,  Shield client

Viewing a 20mbps iptv stream.  I had the max bitrate set to 21mbps and stats for nerds said source was 20 and stream is also 20.  

However when I set the max bitrate to 15, it shows a transcode reason of video bitrate over limit which is correct, but it is knocking it down to under 5 mbps instead of near 15,

Anything under 21 max does the same thing. 

I have attached the ffmpeg transcode log.

Thanks!

MaxBitrateIssue.txt

[Luke 42086]

We are passing in 15mbps so the output is just whatever you get from the encoder. Most likely the input source is not a constant 15 mbps but rather 15mbps could be the peak value, and at times it could potentially be much lower than that.

[BillOatman 596]

@@Luke With the max set to 21, I see a better quality picture and geek stats shows a constant 20mbps, so I don't believe it is the input stream.  I also tried with a few streams, same results.   It's only when transcoding is necessary to a lower bitrate that it drops all the way down to 5mbps.

Is there anything in the ffmpeg transcode log to show why?  There are a whole lot of these for example:

Past duration 0.991997 too large

 

 

Is there anything I can do to improve that?

[Luke 42086]

With the max 21 it's not transcoding at all so it's not really an equivalent comparison. That's just the way the encoder works with variable bitrate encoding. If you lower the server crf transcoding setting, you'll get a higher output bitrate, albeit at the cost of bigger output, and the potential that it won't play smoothly.