I convert my blu-rays using RipBot and generally apply the same settings for everything, typically CF 18/19, single pass at 1080p for a high quality rip - I always prioritise quality over file size.
What I have noticed is that some movies compress MUCH better than others. I was convinced that I had got something wrong with the Social Network as the resulting video stream was about 2.2GB! So I did it again making sure I had my settings correct at CF18 and 1080p. I got the same sized file!
I've had a few others a bit like this, though not to the same extreme. Simpsons Movie was one but I assumed that was down to the bold and limited colours etc. A few other 'proper' movies but I can't recall which ones off the top of my head.
This must be due to the video encoding on the disk, so my question is which formats are most compressible and which are least?
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You are doing some rather extreme compression here in squeezing BD movies which are often over 25 GB in size down to about 2.2 GB. This is a compression of over 10 to 1. I think many here would be doubtful about the quality of your final output, but to each his own. My experience is that generally speaking I think it's possible to squeeze BluRay down to about DVD DL size and still have it look really good. Below that you better be changing the resolution to 720p. Animation will always look good at lower bit rates. I'd argue that you can ever get really good results from old VCD format for animation. Today's HDTVs have various filters on them that make just about anything look good, but if you get very close to your TV and look you can see flaws in the videos up close that are not noticeable from a normal viewing distance.
MPEG-2 is legal for BluRay but not used much. It usually only used when porting old DVD extra features to BluRay. I would expect it to compress quite well when using H.264. I would not expect VC-1 and H.264 to look all that great if compressed at 10 to 1 or more but quality is subjective. An old friend of mine used to make over the air TV recordings a few years ago from a terrible quality analog signal AND he saved them in VCD format. I would rate what he was getting as "horrible" and "unacceptable" and worth viewing only if there was no other way to watch it and you really wanted to see it. But he was quite pleased with himself and the "quality" of what he was getting.
It's not just the format/container. It's also the content of the video and the nature of video compression itself.
Video with a lot of static scenes featuring people talking will compress much better than action stuff where there's a ton of motion.
I know it's an extreem compression.... I'm not asking RipBot to produce a file that small. I select CF 18 single pass so I should have a bigger file and generally I do. However, for certain movies I get a smaller file...
By my understanding setting ripbot with a CF 18 and single pass I should be getting a high quality MKV.
My question is why with certain moves do I get a much smaller file - it's like some stuff compresses much better. My example of the social network does indeed look very, very good even though it's a worryingly small file size.
Less motion, less detail, less noise, less frame-to-frame changes, all these things lead to better compression when using CRF encoding. This is why cartoons and anime usually compresses better than live action material. Attached is six minute 1920x1080, 24 fps, "movie" compressed to a little over 3MB (so a 90 minute movie like this would be about 45 MB). It looks fine. Yes, it's boring but it gets across the point. The fewer changes there are from frame to frame the better the video compresses. This is the beauty of CRF encoding -- you don't have to guess at what bitrate you need to maintain the quality you want.
Last edited by jagabo; 12th May 2012 at 09:43.
Noise is bad for compression. Look carefully at the live action films you're converting - does the noise/grain vary much?
Social Network was shot digitally with Red cameras, so there could well be less noise compared to movies shot on film stock.
I just downloaded a trailer of the movie and there's very little grain. This isn't conclusive, the trailer could have had noise reduction applied. But the video bitrate is nearly 10Mbit/sec which should be enough to reproduce grain in the original footage.
ehhh this is starting to make more sense now... thanks for all the help!