Video Levels


musicvid10 wrote on 5/15/2014, 8:58 AM
Having been forced to transition from analog to digital audio production some years back, I can only sympathize with video producers and broadcasters who automatically think and speak in terms of analog broadcast principles and theory.

It is a different technology. Like VU levels, IRE had a soft ceiling. And broadcasters of yore would push it until TVs buzzed and displayed white lightning. Today that is no more, right along with +6 VU.

Whether or not broadcasters still speak in percentages, publish clamped or loose submission standards, post-level or reject too-hot video, it's all BT 709 or stricter when it hits the pipe. That's (16-235 luma, 16-240 chroma), at least in ATSC land. (Note: Saying "104% chroma" is already a little too hot for BT 709, or so it seems).

Nowhere in BT 709 are the deprecated IRE references mentioned, nor are VU audio levels, and correctly so.
Former user wrote on 5/15/2014, 9:04 AM

I have worked in TV a long time and I never knew any broadcaster who pushed white levels. You couldn't do it. First off, most video switchers used a proc amp that would clamp levels at 100, maybe 102. ( I am talking lumance, chrominance was a bit different) Second, broadcasters normally have a clamp on the transmitter end so if the video did get out at over 100, it got clipped at the transmitter level.

Chrominance was usually allowed up to 110.

The main reason for video being sent out hot was if the tape op did not set up to bars correctly. But see second above.

Most buzzing that you heard on a TV was caused at the receiving end by a poor antenna or TV.
musicvid10 wrote on 5/15/2014, 9:09 AM
I endured rural ground broadcasting for most of my early life (late fifties through sixties). I sincerely doubt all the engineers were qualified or the equipment monitored. With one or two stations for every sixty mile radius, you know they pushed everything.

Mostly prevalent during locally-produced commercials, when the scene switched to white background or text. No doubts about the source of the problem.

I should have mentioned that not all of those splattered whites were pushed deliberately; and at what point in the chain they occurred I surely won't debate. However, they sure were nasty!

And I hope you don't feel that I'm criticizing your frame of reference. Shaking the analog mindset for me was just a little harder than quitting cigarettes.
Former user wrote on 5/15/2014, 9:45 AM
"And I hope you don't feel that I'm criticizing your frame of reference"

No not all. I would guess some stations were more lax than others. And video engineers (specifically cameramen) always wanted to push levels. And film graders would push them as well, but as an editor I had to reign them in. We actually had our proc amps set for 106 so we could see what was getting clamped and adjust accordingly.

In the digital world, I don't see that there should be limits since digital has limits built in (try to go above 255 white levels ;) ). But as I stated in an earlier post, in the US we are always concerned about backward compatibility. Witness the Color TV transmission (bringing us 29.97 instead of 30fps), Stereo (had to mix down to mono correctly), Widescreen (graphics must be 4x3 safe). I think in other countries they just tell people to move on or suffer but in the US we always worry about the viewers who are behind in tech.

I think it is time to allow the specs to match the tech, but I am not in any position of power to do it. Most of my work these days is for computer streaming or theater so the broadcast standards only apply as far as the limitations of the equipment being used. I generally don't worry about the setup or levels like I used to because the equipment is not concerned.

But here is also a concern about this issue. There are a lot of very respected people on this posting who can't agree on how it should be done. I respect Glenn, Chienvideo, Musicvid and others, but they all have different points of view and good reasons for them. so how could anyone who is less qualified know what the traps are and how to avoid them? Until we become ALL digital (from acquisition to delivery) with digital specs, we will never agree.

Just my thoughts.
musicvid10 wrote on 5/15/2014, 9:52 AM
"Until we become ALL digital (from acquisition to delivery) with digital specs, we will never agree."

That's a point of agreement, Dave. 0-255 broadcast delivery would mean more colors on the screen without everyone switching to UHDTV; reworking the 6 Mhz bandwidth rule would be a bit of a pain, though. Maybe h265/HEVC will eventually get us around that.
Marco. wrote on 5/15/2014, 10:08 AM
You can't use Vimeo for a demonstration because then happens exactly what should not been done with the signal: computer based processing. It's meant for a test on purely digital video equipment: DVD and Blu-ray-disc player, hardware media player, HDMI connection, LCD TV panel. Nothing else. If it runs through a processing like the player involved by Vimeo distribution, it is – of course – very likely studio swing will be stretched to full swing thus clipping the signal (but all depends on the setting of your grafic device in this case).

To distinguish between computer and video based processing is as important as to distinguish between peak levels and reference levels.
Marco. wrote on 5/15/2014, 10:38 AM
Yes, BT. 709 lacks several details and one is the distinction between reference and peak levels. It says the values 16, 235, 240 are the nominal peaks. It also says video level quantization is in the range of 1–254.

Though it is not recommended to use BT. 709 solely to determine production conditions. BT. 709 completely lacks any reference to the EOTF, which is even more important for production. I would never use BT. 709 as only reference without also using BT. 1886 and EBU Tech. 3320. BT. 709 alone makes limited sense once a signal is quantized/digitized.

Unlike computer levels, giving and retaining footroom and headroom is one of the most important property of digital video levels. The core of this discussion was the way Vegas Pro handles video levels. Vegas Pro just keeps footroom and headroom unaltered. Input = output. Many people, me included, appreciate this. Different surroundings, different equipment, different purposes – different meanings. Not just one truth.
musicvid10 wrote on 5/15/2014, 10:42 AM
"Many people, me included, appreciate this."
I think you can safely include me, atom12, and a few others in sharing that sentiment.
Former user wrote on 5/15/2014, 10:45 AM

I agree as well, but people have to realize that is what it is, footroom and headroom.
Marco. wrote on 5/15/2014, 10:51 AM
So – without limitation – we all earned a cold beer this evening :D

I'm curious now to what extend there might be differences in video hardware equipment (how devices like DVD-players, Blu-ray-disc players, media players, HDMI handle levels outside 16–235) between EBU und US.
Former user wrote on 5/15/2014, 10:58 AM
All of my DVD players clip black at 16 (7.5). I am not sure about the whites.

musicvid10 wrote on 5/15/2014, 11:12 AM
What dvd players do can depend on the output method (analog or hdmi). And they all seem to be different, and also can have user settings.

One of my old dvd recorders set up the blacks a second time, giving me 33.
GlennChan wrote on 5/15/2014, 11:13 AM
Glenn, I'm trying to get my head around your suggestion. I'm curious how you think this should look in Vegas if everything came in correctly. Assume I have these three media:

1: Vegas would know where black level is supposed to be and where white level is supposed to be. A sensible setup would be to put black at 16 16 16 rgb and white at 235 235 235 rgb.

The JPEG image will get converted so that its blacks are at 16 rgb and white is at 235 rgb.
I don't know what you mean by "MTS video" (DVD???). There are standards that govern video formats. For Rec. 601 and Rec. 709 formats, both white and black level are defined. So Vegas should respect the spirit of that standard. These standards exist so that people don't have to deal with situations like what you experience in Vegas today.
If there are superwhites in the original footage, they should stay as superwhites (as the default behaviour). If the user wishes to manually bring the superwhites into legal range, they can manually opt to do so. This is how other NLEs handle it.

2: When you export, Vegas should correctly map your black level to the correct black level.

Other NLEs already do this. The concept of having to convert between studio and computer RGB doesn't exist in those NLEs.

*There was a time where FCP would screw up with dSLR footage. But once the codec got fixed, that issue was solved.

The big picture is this. Because other NLEs handle levels conversions for you (in a standards-compliant way), it frees the user to do other things. You never think about this stuff because the NLE handles it for you.

When you specify white in Final Cut Pro... you get white. You don't get a light grey, white, or an illegal white.
If you use the color generator preset in Vegas for white... you will either get white or an illegal white.
If you use the color bars generator in Vegas... maybe the color bars will be correct. Or maybe not.
If you use the waveform monitor in Vegas.... maybe it will be correct. Or maybe not. Years ago, I had access to a real set of hardware scopes (with SDI in) so I was able to figure out how Vegas' levels worked. Don't trust the waveform monitor in Vegas. It can be useful but do not use it to figure out levels.

That's madness in my opinion. The way Vegas does things is inconsistent, unintuitive, confusing, and error-prone. That's why I keep saying that Vegas should handle levels automatically for the user. Clearly, this is too difficult even for advanced Vegas users.
Marco. wrote on 5/15/2014, 11:13 AM
I think clipping black near the very end of the pipeline could be fine, if not intended to carry special test patterns like the PLUGE signal. The well-adjusted TV panel would not display super-black anyway.

But headroom is different, so I usually only test the headroom area (and only digitally connected via HDMI).
musicvid10 wrote on 5/15/2014, 11:15 AM
MTS means standard AVCHD from a camcorder.
Typically 16-255 without user intervention.

7 billion phones and devices do not respect BT 601/709 standards. Most of them do not employ VUI flags, So in order for Vegas to be "automatic," it would have to do more than honor the colorspace flag. Allowing the highlights to clip is the same as doing nothing.
Marco. wrote on 5/15/2014, 11:18 AM
Are you refering to black and white peak levels or to black and white reference levels? A system can not automatically detect what the intended white reference level is, nor can it differ between a pushed reference black and noise below reference black.
GlennChan wrote on 5/15/2014, 11:29 AM
Yes, BT. 709 lacks several details and one is the distinction between reference and peak levels. It says the values 16, 235, 240 are the nominal peaks. It also says video level quantization is in the range of 1–254.
BT. 709 defines 10-bit video. It never talks about 8-bit video.

Vegas Pro just keeps footroom and headroom unaltered.
That's not really true. If you import footage video via a codec that decodes to computer RGB, then you will lose superblacks and superwhites.
Quicktime Prores (e.g. if footage was captured on another system) into Vegas might do this.

Input = output.
Again, not true.

You can take the same footage and export it to different formats. It is possible to create situations where the same footage will decode to different levels in Vegas.

You're confused because you don't understand.

Look... I wish this stuff wasn't so confusing and unintuitive. That's why I'm saying that the NLE should handle this stuff for you. That way, you don't need to worry about converting levels correctly.

(*There will still be situations where you need to manually intervene, bugs, etc. Cameras shooting superwhites will be an extremely common issue that you still need to deal with. But there will be many other issues that you just won't need to worry about.)
Marco. wrote on 5/15/2014, 11:35 AM
Quicktime ProRes is a rare exception. Any variant of H.264, any variant of XDCAM/XDCAM HD/XDCAM EX, MPEG-2, HDCAM SR, uncompressed (also the YUV variant), P2 works in the way input equals output.

"BT. 709 defines 10-bit video. It never talks about 8-bit video."

Are you sure we mean the same doc? I did not re-write these values mentioned. I did a copy and paste from the document I directly downloaded from the ITU (no Wikipedia nonsense). In chapter 6 of "Digital representation" it clearly talks about "8 bit coding" while 10 bit is only mentioned in a small side note.

Isn't it funny if someone says others do not understand?
GlennChan wrote on 5/15/2014, 11:45 AM
MTS means standard AVCHD from a camcorder.
You're making things needlessly confusing.

There is no NLE in the world that will by default map 16 Y' to legal black and 255 Y' to legal white. Vegas shouldn't either. That behaviour would be madness.
GlennChan wrote on 5/15/2014, 12:01 PM
I'm going to bow out of this discussion. I don't know why anybody would argue that Vegas' handling of levels makes sense.

The simple truth is this:
-Other NLEs handle levels sensibly.
-Vegas doesn't.
-I wish Vegas handled levels sensibly. I know that there are a lot of Vegas users out there who are confused. Or, they have been burned by some unintuitive behaviour that they didn't know about (there are so many of them). It shouldn't be like that.
Marco. wrote on 5/15/2014, 12:14 PM
To me and many others sensible level handling means: not mapping levels and not clearing footroom and headroom before I tell the system to do so.

Except of rare exceptions like the ProRes processing you mentioned (and same is for another certain flavor of MOV files), for many people Vegas does a good job. And probably no one would reject some nice new options in Vegas Pro so it would also fit other's preferences.
VidMus wrote on 5/15/2014, 12:14 PM
"You can't use Vimeo for a demonstration because then happens exactly what should not been done with the signal: computer based processing. It's meant for a test on purely digital video equipment: DVD and Blu-ray-disc player, hardware media player, HDMI connection, LCD TV panel. Nothing else."

Sorry Marco., but the mp4 videos before they were uploaded to Vimeo are exactly the same. I can render for DVD and get the same results when played back on my TV's. It has absolutely nothing to do with Vimeo.

The video levels above 235/100 IRE gets chomped off no matter how I do it.

When going from sRGB to cRGB on my external monitor all levels above 235 are chomped. If I turn off the conversion, the levels above 235 will not get chomped off but then the external display will be wrong in the same way as the little viewer is.

This whole thing reminds me of the confusion caused by multiple systems in place throughout the world. There is the USA system, the variation of that in Japan and then the others. Beyond the levels is the frame rate in various systems and countries. The USA system has that awful backward compatible mess as well.

So what works a certain way where you are does not work that certain way where I am.

It would be great if we could ALL get one universally compatible system that we can all use without all of this mess. But then good luck on getting everyone to agree on one universally compatible system!

I do what I need to do to make my videos work in the USA. I know what my cameras shoot and I know what the NTSC color bars consist of in levels and colors, so I know what I need to do to get the desired results here in the USA. And I do get the desired results I want.

Marco. wrote on 5/15/2014, 12:19 PM
O.k, I see what you mean. Strange.

"I can render for DVD and get the same results when played back on my TV's."

Is your player connected via HDMI?
larry-peter wrote on 5/15/2014, 12:27 PM
If Vegas allowed "automatic" level handling as an option, maybe everyone would be content and its user base would increase. Those would be good things. I respectfully request the option to continue in the current manner.

The points made above about the analog > digital transition in TV workflow resonate completely with me. Human knowledge and intervention were always necessary to ensure the highest quality transmission of a recorded signal. Many times, relying on solely on the equipment resulted in an inferior broadcast. I've witnessed it too many times. Moreso today than in the analog past, actually.

Basically, I'm too old to relearn NOT to check and intervene. Even if Vegas handled levels automatically, and did it perfectly, I would still be checking levels on every imported clip on the timeline. Maybe I would save some keystrokes by not applying my presets as often, but I'm conditioned to take responsibility for the program. I was told that was my job from the first time I entered an analog online suite.

Perhaps in my next life I'll believe that software can do it better than I can.