Vegas video levels - debate possible changes


musicvid10 wrote on 4/28/2014, 8:58 PM
"Common users could use some docs on levels and some help/prompt/wizard."
Yes, I agree.
That was a driving force behind the video tutorial we produced in 2011.

Can you show me a MediaInfo of some AVC that is "flagged full range"? Libav works exactly the same as any other encoder with everything I've given it.

Unfortunately, many more things come into play besides seeking min/max levels. That would be easy. The thing these algorithms are unbearably slow (and terrible) at are putting any meaningful attributes to those levels. Are they wrong or were they meant that way?

Compressed ranges in high- and low-key scenes are essentially impossible to distinguish from overexposure and underexposure, respectively. Beach scenes, fireworks, sunsets, overcast, white cat in a snowstorm, black cat in a coal mine, all fail 90% of the time. Likewise, high contrast scenes reveal nothing to scan algorithms about whether the subject is frontlit or backlit, or just has specular highlights which should be ignored.

A switch for preview and "perhaps" output is really all we, or any amateur (along with a little education), need. Anything more just compounds confusion and adds time to the workflow, which I'm certain nobody wishes for. I'll be done with this thread though, thanks for compelling us (and Sony) to take a third look.

[Edited for detail}
Former user wrote on 4/28/2014, 9:15 PM
I am not being an advocate of FCP, but they use the Zebra to indicate that your video exceeds 100 (much like a camera), I would think that this same type of thing could be done for blacks that are too low in Vegas.

In FCP you can turn this off or on.

musicvid10 wrote on 4/29/2014, 12:06 PM
The "AVC VUI flag" you mentioned turns out to be nothing but the x264 fullrange switch in this context, which has been around forever, as far as I can recall. What it doesn't do is alter encoding levels. It is a decoder flag only, one that has found very limited support.

In fact, when I discussed this with Handbrake developers a few years back, we could only find a couple of players that even recognized it.
As a user flag, it could (and probably would) be used incorrectly, which would add even more confusion, not less.

x264 is an open source, GPL library. For that reason, it is unlikely Vegas would ever support something like that. I'm curious though; what camcorders actually shoot x264, much less invoke the fullrange decoding flag?

I appreciate your willingness to explore and learn, yet a lot of this territory has already been covered.

We need a preview switch, not a Goldberg solution.

(Zebras or a "show clipping" option would be kind of cool, though.)
GlennChan wrote on 4/29/2014, 11:04 PM
The engineer Marc S is talking about is me, I think. :-) If I seemed underinformed on the topic at NAB it's simply that color and levels are not my area of expertise -- I have a reading-level knowledge of the topic, but not expert level. I assure you, it's not a deliberate attempt to ignore the problem!

I've bugging SCS to have Vegas automatically handle levels for a very long time now... lol. I sent some notes to Dave Hill on how to do it.

A lot of NLEs automatically convert levels for the users so they don't notice this stuff or have to worry about it*.

*There are situations where you do have to worry about stuff that you can't see in the NLE's interface like superwhites, superblacks, and levels that aren't broadcast safe (if your material is going to broadcast). Even if the NLE handles levels for the user.


The reason to do this is to make the program easier to use. Clearly getting users to manually convert their levels correctly is extremely hard. There have been very long debates on this forum.

I've posted part of the answer here:
It's pretty ridiculous that the right way of doing things involves consulting a giant table. And I don't even get into how the compositing modes are screwed up or why the video scopes are screwed up (there should be a line at 7.5 if the 7.5 IRE checkbox is checked).

Making Vegas handle levels correctly would really help make it more intuitive to use. There are a lot of unintuitive behaviours that SCS could eradicate.

It will take work because you have to:
- make a new project setting
- write code to understand the levels coming from different codecs (including the weird full range Y'CbCr stuff from DSLRs) and what levels the codecs expect
- automatically convert levels
- revamp filters
- have filters understand whether the project has everything converted into studio or computer RGB
- revamp the compositing mode
- make changes in Vegas wherever you have a checkbox or setting for "studio RGB"
- add a 7.5 line to the video scopes
- possibly implement dithering (I'm not sure I would do this)
- think about whether you should allow Vegas to passthrough DV and HDV. When Vegas renders a cross-dissolve, that cross dissolve will be limited to computer/studio RGB space. The video on both sides of the cross dissolve may be in Y'CbCr space. Studio RGB color space is smaller than Y'CbCr and I believe you'd be able to see this on a CRT TV. (And yes, some/many cameras shoot levels that fall outside of studio RGB.)
- revamp the color pickers
etc. etc.
GlennChan wrote on 4/29/2014, 11:25 PM
The document for Rec. 709 describes a 10-bit format, not an 8-bit format. The highest and lowest codes are reserved for synchronization signals.

In esoteric situations that might matter because you will realize that 255(Y') from an 8-bit format gets clipped in certain workflows. Esoteric situations involving really expensive gear where you are sending video over SDI or dual-link SDI. (Situations I honestly wouldn't worry about.)

2- In general, there is so much misinformation on this forum about video engineering. The subject is inherently unintuitive so I can see why people are confused.
TeetimeNC wrote on 4/30/2014, 8:24 AM
>(Zebras or a "show clipping" option would be kind of cool, though.)

I would really like to see the show clipping option as implemented in Lightroom so we can see clipping in both highlights and shadows.

NormanPCN wrote on 4/30/2014, 11:01 PM
The "AVC VUI flag" you mentioned turns out to be nothing but the x264 fullrange switch

The AVC/H.264 VUI flag is nothing created or defined or unique to x264. It is defined within the H.264 spec.

You can see the definition in a publically available ITU document here.

x264 as an H.264 encoder is simply exposing this VUI option, and other VUI options, for those that may want to define it.

I can't see myself ever wanting to define that in an encode.

It is a decoder flag only, one that has found very limited support.

My previous posts talk about products that certainly seem to support this flag.

I have never proposed that Vegas would output this flag. I only proposed that Vegas, like others, be capable of using this information at the users request. Never automatic.

what camcorders actually shoot x264, much less invoke the fullrange decoding flag?

My previous posts list some that output the flag.

Here is a dump the MediaInfo developer sent me from a Canon DSLR file I sent him.

musicvid10 wrote on 5/1/2014, 12:13 AM
So, that's the solution?
Shoot or encode everything at 0-255, set the flag, and everything will be fine?

Sorry, it just didn't work that way for me, in hours of testing. Still plays clipped and decodes 0-255, whether Canon DSLR or anything else.

What could I possibly have done wrong?

farss wrote on 5/1/2014, 12:44 AM
False colour metering is way more useful in post, not used much in cameras.
It isn't that hard to work out what clipping using a waveform monitor, false colour metering lets you see where things are siting as well as what's clipping.