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Extreme Variation in File Size

Posted: Tue Aug 13, 2019 12:35 pm
by Blatherscribe
Greetings,

I was hoping someone might help me understand why my Handbrake-finished files show such a wide range of file sizes after being transcoded with the same settings. I'm using RF 18 and the "veryslow" transcoding speed. Most Blu-Ray movies start at around 28 GB, and end up at 8 or 9 GB. But some have been as low as 5.5 GB (full length, full size Blu-Ray), and just last night one wound up at 16 GB. That 16 GB file also took more than four hours to transcode, when usually it takes about 125% the running time of the film to transcode. For a final piece of strangeness, the movie that took twice as long and wound up twice as large as usual wasn't a special effects extravaganza made last year, it was the Muppet Movie (1979).

Any ideas about why this might be so?

Thanks!

Re: Extreme Variation in File Size

Posted: Tue Aug 13, 2019 12:55 pm
by Ritsuka
Random noise or grain can't be easily compressed. Older movies usually have more video grain.

Re: Extreme Variation in File Size

Posted: Tue Aug 13, 2019 2:33 pm
by BradleyS
Try the NLMeans denoising filter to clean up the video and make it more compressible. It's slow but you will likely turn that 16 GB encode into something much smaller.

Re: Extreme Variation in File Size

Posted: Tue Aug 13, 2019 3:30 pm
by mduell
Gee if only we had an encode log to see what happened.

Re: Extreme Variation in File Size

Posted: Tue Aug 13, 2019 3:39 pm
by Ritsuka
Does the activity log show how much grain is there in the video?

Re: Extreme Variation in File Size

Posted: Tue Aug 13, 2019 3:55 pm
by mduell
Ritsuka wrote:
Tue Aug 13, 2019 3:39 pm
Does the activity log show how much grain is there in the video?
Does it tell us definitively what settings OP used? Yup
Does it report definitively what the encoding outcome was? Yup.
Are there a lot of heuristics in there we can use to make a more educated guess if grain is the real problem? Yup.

Re: Extreme Variation in File Size

Posted: Wed Aug 14, 2019 6:11 pm
by Blatherscribe
Thanks for the responses. I didn't post an activity log because I was asking a general question rather than a tech support one. I've looked at it, and it doesn't say anything about grain, possibly because I didn't use either denoise filter. I've seen examples, and while it does remove film grain, it also tends to make the images look a bit flat and smeared, at least in my opinion.

The Muppet Movie, for what it's worth, has an absolute ton of film grain. So I'm sure that's the reason the file is so large. Thank you for explaining that! I didn't realize it would be such an issue, but in retrospect, it does make sense. It's not really predictable, so the program can't compress and extrapolate frames.

I'm still a bit puzzled about why one movie would wind up at 5.5 GB and another at 9 GB when both were made around the same time, but I'll just chalk that up to the mysteries of compression.

Thanks again. :)

Re: Extreme Variation in File Size

Posted: Wed Aug 14, 2019 6:39 pm
by JohnAStebbins
I've seen examples, and while it does remove film grain, it also tends to make the images look a bit flat and smeared, at least in my opinion.
Have you looked at examples of the NLMeans filter specifically? This filter is very good at removing noise without the side effects you are concerned about. You should at least try encoding a short example for yourself and look at the results with *your* video.
I'm still a bit puzzled about why one movie would wind up at 5.5 GB and another at 9 GB when both were made around the same time, but I'll just chalk that up to the mysteries of compression.
A lot of things contribute. Sometimes the original source was better preserved. Sometimes the content is processed during the transfer to disc. Noise isn't the only contributing factor to size variation. High detail (trees, flocks of birds, etc), high motion (chase scenes, flocks of birds in flight) will increase file size.

Re: Extreme Variation in File Size

Posted: Wed Aug 14, 2019 7:18 pm
by Blatherscribe
Thanks for the suggestion. I tried that filter, and it has to be cranked up to maximum to make a noticeable change, by which point the image quality is diminishing. I'll just live with the film grain. At least it's real, not the special effect they add to some video games. :)

Re: Extreme Variation in File Size

Posted: Wed Aug 14, 2019 11:32 pm
by mduell
Don't crank it up to the max. It can be quite effective at reducing size without drastically changing the image.

Re: Extreme Variation in File Size

Posted: Thu Aug 15, 2019 12:20 am
by BradleyS
The NLMeans Grain tune specifically does not process the luminance channel, only the chrominance (color) channels. This can reduce color noise and splotches and as a result, reduce file size while preserving the appearance of grain without smearing.