On Thu, 16 Jun 2005, Matto Marjanovic wrote:
> "If mpeg2enc is told to encode N seconds of material with a target
> bitrate of M bits/second... then the resulting file should be
> roughly the N*M bits long, no matter what it is encoding."
Well - that's not how it read ;) What was written was far too
easy to read as: "that's bits/frame and you don't know what units
you're using".
That has the builtin assumption that all the bits it was given
were being used, right? If it's 'under budget' at 30fps then
reducing the amount of data to be encoded by 20% should result
in being even further 'under budget'. Right?
> One would expect the _quality_ of the encoding to vary though. With the
> 24fps input, mpeg2enc should have more room in the same file to store
> real information. With the telecined input, mpeg2enc will squander
> some of its limited bit reservoir in encoding those redundant fields.
Is it reasonable to say:
If it's not bitstarved in the first place (i.e. isn't using
all the bits it was given) then reducing the amount of data
substantially should result in a smaller (even less bitstarved)
file?
It could well be that the tape was noisier than it looked even
after being cleaned up before going off to mjpegtools-land where
it was run thru y4mdenoise.
If the difference had been even a little larger (5-10%) I'd probably
not have even bothered discussing it. But 1% even with a few
variations on parameters was an anomaly worth exploring.
Maybe it was more bitstarved than it appeared at first glance - I'll
give another tape a try this weekend and see what happens with that.
Steven Schultz
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