How accurate is my idea of bitrate/filesize estimation?

General questions or discussion about HandBrake, Video and/or audio transcoding, trends etc.
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Silent_Strider
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How accurate is my idea of bitrate/filesize estimation?

Post by Silent_Strider »

Hi everyone,

especially with older movies, and especially with upscaled BluRays, it is (at least for me) often difficult to imagine, which RF quality one should use.

For example, once I encoded Mary Poppins with RF 21, Preset Very slow. The source file was something like 28 GB. And the encoded file was... 26GB. Yeah, maybe RF 21 wasn't this great, but it's just to give an example.

So it took quite a while to encode and it wasn't worth anything to wait for.

Soo... I wrote myself a little batch file, which does the following:
Every 10 minutes it cuts a 1 minute sequence from the video with ffmpeg and saves that 1 minute video as a temporary file. Then it uses mkvmerge to stitch all 1 minute videos together to a new file and delete the 1 minute videos in the end.

So e.g. if the movie is 95 minutes long, I will have 9 minutes of the movie with bits from every part of the movie.

Do you think it is somewhat reliable to test RF settings with this smaller bit of video and then just assume the filesize times 10 for a final movie? Making test encodes with only 10% of the movie can make it quite faster to test around with some settings I believe.
mduell
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Re: How accurate is my idea of bitrate/filesize estimation?

Post by mduell »

Sure, it will get you some reasonable result. 95% confidence within 1%? Probably not.

But why are you doing this in the first place?
If you want to keep the grain, you should use the grain tune, and expect large output files.
If you want to obliterate the grain, use nlmeans filter with the grain tune, and expect smaller output files.
If you want some specific file size (due to limited media size or something), use an average bitrate target based on the movie length.

Or if you're "really sophisticated"/borderline insane, use or adapt Don Melton's Video Transcoding tools to suit your min/max quality and min/max output size preferences.
Silent_Strider
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Re: How accurate is my idea of bitrate/filesize estimation?

Post by Silent_Strider »

Sounds like it would be difficult to keep the grain, but also get a reasonable size?

My thought was, when I found out, that I e.g. need RF 28 for a reasonable size, how bad can it really be on an already grainy video to use the "lower" quality?
Woodstock
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Re: How accurate is my idea of bitrate/filesize estimation?

Post by Woodstock »

The more detail you ask the encoder to preserve, the more bits it takes to do it. Grain (actual grain, not artificially-produced) and "static" (think old movies from damaged prints) exhibit a lot of movement, so that needs to be accounted for.

Raising the RF level tells the encoder to toss out more detail. Using a noise filter tosses out detail before the encoder sees it.
rollin_eng
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Re: How accurate is my idea of bitrate/filesize estimation?

Post by rollin_eng »

Silent_Strider wrote: Fri Mar 19, 2021 8:01 pm
Do you think it is somewhat reliable to test RF settings with this smaller bit of video and then just assume the filesize times 10 for a final movie? Making test encodes with only 10% of the movie can make it quite faster to test around with some settings I believe.
The only real way is to try it out.

I did some file size estimations here:

viewtopic.php?f=14&t=34831
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