What exactly is "fudge-factor"?


#1

Looking at logs from people in the forum having transcoding issues I noticed that many times there's a log line similar to "Scaled up video bitrate to xxxx Kbps based on 1.500000x fudge factor". What exactly is this "fudge factor"? And how it impacts the "direct-playability" of movie files?


#2

File Bitrate = the bitrate value sampled from the file itself when its imported into Plex. (aka, when its analyzed) as this is an average value, or even a sampled ranged of values, it's going to be lower than the peak bitrate. (i.e. it wont catch every single bitrate spike in the file)

Calculated Bitrate = the max bitrate value used by Plex when calculating things like bit-rate limits. It needs to be higher than the average bitrate as the last thing someone wants is for spikes in the bitrate to exceed available bandwidth and have buffering in the stream.

Fudge Factor = a multiplier applied to the File Bitrate to cater for the spikes and give an assumed "Maximum" value. AKA, its a quick simple way to take a guess at the peak file bitrate.

File Bitrate x Fudge Factor = Calculated Bitrate.


#3

@trudge said:
Fudge Factor = a multiplier applied to the File Bitrate to cater for the spikes and give an assumed "Maximum" value. AKA, its a quick simple way to take a guess at the peak file bitrate.

File Bitrate x Fudge Factor = Calculated Bitrate.

So this line with fudge factor etc is always present, even in direct play cases? I mean, If I got it right the fudge factor is always applied to have an estimation of peak bitrate and then compared to the required bitrate by the client to see if some transcoding to lower bitrate is necessary. But if there's no such limit and if there's direct play enabled, this calculation should not have consequences.


#4

why would direct play v transcode make any different when it comes to this? The same logic applies to both. (this is part of the decision to transcode or not)

the file bitrate is the same
the peaks in it are the same
the limits are the same (if there is no limit, it's still the same)