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Old 06-12-2017, 05:05 PM   #1
zvit
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Default Is 25Mbps bitrate quality just an illusion

Many have suggested exporting offline files at bitrates of 25-30 Mbps for 24,25,30 fps for 2k video and 35-45 Mpbs for 4k with the same frame rates. (4k resolution needs to compress more data into every second thus needs more bitrate to maintain quality).

The reasons given? Not very clear. Usually "it looks great", "it's good enough", "no need for higher bitrate"...

This is a general question about the suggestions all over about getting the highest possible quality from your export. Your final destination and use of the file will be the main factor to your export settings but let's simplify this with a simple example. In this post I am asking about bitrate only - even though resolution, codecs and other things will also determine final quality.

1. You want to export a 2k video file for offline viewing only.
2. You chose all other settings, say H.264 mp4, CBR, etc.
3. You don't care about the export time or file size. Your goal is to get the highest quality possible with your bitrate setting (but you don't want to export RAW).
4. Let's say it's a video of a wedding so it will be watched on a large screen TV.

The question:
Why is 25-30 Mpbs a magic number?
Will bumping up the bitrate to a crazy number like 100 give better quality but maybe can't be noticed to the human eye? Or is there a limit to how much bitrate can actually be compressed into a 2k video? If so, is 25-30 really the limit or do people just use it because they got used to it (like me)?
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Last edited by zvit; 06-12-2017 at 07:28 PM.
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Old 06-12-2017, 06:59 PM   #2
Liverpool TV
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Hi Zvit.

25Mb is easily enough for high quality HD at the standard frame rates you mention. Even Edius' own H.264 is now very capable at these rates for most types of content.

If you use the X.264 plugin for Edius, then you'd get away with even less bitrate for high quality H.264.

For UHD Edius can still produce great results between 20-30Mb, content dependent. Again though, the plugin would allow for very high quality at low bitrates.

If you want maximum UHD quality at low bitrates of around 25Mb, then you'd after go outside Edius. As you'd need to use at least H.265 and Edius doesn't have this ability, I may be wrong but I don't think the X264 plugin can do it.

That said. The best way to achieve maximum quality UHD at low bitrates would be to use VP9. This is an awesome codec for UHD. Even if you don't have a VP9 encoder to hand you can try it with YouTube, and its average bitrate is below 25Mb.

Just create a short HQ/X file of maximum quality and upload it to YouTube then rip the UHD version that YouTube produces. The pictures are quite stunning for such low bitrates.

This post actually covers everything you've asked about and there's a bunch of comparison UHD bitrates you can download, including YouTube encoded VP9.

https://forum.grassvalley.com/forum/...ad.php?t=39964

The Edius only encodes from this test are in the following post, for anyone not logged in or for anyone browsing the forum without an account who can't access the lounge.

https://forum.grassvalley.com/forum/...ad.php?t=39965

The posts will explain the point of the tests etc. But for what you're looking into, they're probably good for giving like for like examples of low bitrates across multiple encoders. Due to the very low bitrate nature of some of the encodes, they show up artefacts between the different methods, which helps to visualise and gauge the differences. High bitrates would be more of a leveller and probably wouldn't help with your questions regarding low bitrates.

Cheers,
Dave.
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Last edited by Liverpool TV; 06-12-2017 at 07:24 PM.
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Old 06-12-2017, 07:37 PM   #3
zvit
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All great answers - thanks.

But my questions wasn't on how to get great quality with lower bitrates. My question was more technical, or say "geeky".... Say I don't care to have huge bitrates. Don't care about the file size. Just want to know if giving it a crazy bitrate would end up giving even better quality - that a viewer would notice.

More4K wrote "at the beginning quality increases a lot with bitrate, but after some point you need a lot of bitrate to increase quality further..." so yes, let's bump up to 100Mbps and increase quality further... or will this really be the case?

Is there a point to increase bitrate to even more than the raw footage was filmed in? Would this be like trying to create something from nothing?

So like I said - I want a family to watch their wedding video on a large TV screen - at the highest quality possible - no matter the file size.
So would it still be preferable to do no more than 30Mpbs? and if so - why? (geeky answer - not solutions :-)
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Old 06-12-2017, 07:59 PM   #4
Liverpool TV
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Quote:
Originally Posted by zvit View Post
All great answers - thanks.

But my questions wasn't on how to get great quality with lower bitrates. My question was more technical, or say "geeky".... Say I don't care to have huge bitrates. Don't care about the file size. Just want to know if giving it a crazy bitrate would end up giving even better quality - that a viewer would notice.

More4K wrote "at the beginning quality increases a lot with bitrate, but after some point you need a lot of bitrate to increase quality further..." so yes, let's bump up to 100Mbps and increase quality further... or will this really be the case?

Is there a point to increase bitrate to even more than the raw footage was filmed in? Would this be like trying to create something from nothing?

So like I said - I want a family to watch their wedding video on a large TV screen - at the highest quality possible - no matter the file size.
So would it still be preferable to do no more than 30Mpbs? and if so - why? (geeky answer - not solutions :-)
You don't need high bitrates low bitrates will do it with the right encoder and settings. Typical wedding videos would lend themselves to lower bitrates and most family members wouldn't notice a proper well done 30Mbit encode compared to a 100Mbit one.
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Old 06-13-2017, 05:19 AM   #5
zvit
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Quote:
Originally Posted by More4K View Post
30mbit is no near to be transparent quality for 2K. It's just good viewing quality video, sort of Blu-ray quality, so fairly good representation of the master.
100mbit x264 for 2K will make you file visually very close to uncompressed.
One of the way to test it is to use lossless mode in x264. This will show you at what bitrate x264 can achieve mathematically lossless video. Going above this makes no sense at all- file is already as good as source and it can't be better :)
Very well explained. All the rest is also clear and understandable. Very good read. Thanks.
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Old 06-13-2017, 08:14 PM   #6
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Quote:
Just want to know if giving it a crazy bitrate would end up giving even better quality - that a viewer would notice.
A higher bit rate normally gives better quality until you reach uncompressed, all other things being equal. But as noted above, some encoders do better than others at a given bit rate.

What a viewer will notice depends on the quality of their playback/viewing system, their vision, and viewing conditions including what they have just viewed.

For HD, somewhere between 17 and 25 Mbps appears to be a point of diminishing returnsfor "average" noise-free material, but as always your mileage may vary. Higher may be better, but the average viewer will not notice it unless specifically coached as to what to watch to for.
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Old 06-14-2017, 09:21 AM   #7
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I'm surprised that one thing was not discussed yet: Constant vs. variable bitrate
I would expect that some scenes that compress well (talking about data rate, not loss of details) would save some "bitrate credits" for scenes that don't compress that well (when following "soon" in the timeline).
Is that the case?
(I have a semi-professional DSC that seems to limit the size of JPEGs (similar to the bitrate constraint in video encoding). Regularly I notice that irregular structures like plain green grass looks like green mud (more or less), even when having selected the highest quality for JPEGs. When taking pictures in RAW format, I don't have that artefact, but on average I'll have to add more works go get images as "crispy" as those JPEGs. So usually I still create JPEGs).
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Old 06-14-2017, 11:39 AM   #8
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Andrew, regarding using VBR, wouldn't that depend on the size or the project, in that a short corporate promo could be encoded at a higher CBR as it will fit onto any small media. Then of course as you elude to, giving someone a file that hits 100Mbit that chokes on a TV is a major problem. I have never found any specs as to what a TVs max bit rates are. Remininscent of the early days of DVD encoding and the well meaning idiots that were encoding high at 8500 and then finding the player fell short of the whitebook spec (or their total DR exceeded it). By 2003 Encoding Guru Ben Waggoner taught me 6500 out of Procoder +AC3!
Max DR for TVs would be helpful...and you can bet they will vary from manufacturer to manufacturer.
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