Advanced Digital Video Part 3)

Welcome back.

We’ll turn on the Wayback Machine and go all the way back to analog video.

In an analog video image, you have different portions of video: active, sync, front porch and back porch.

Most importantly, the pulse sync is a feature that is used to keep the synchronization.

Video receivers and displays look for the sync pulse by detecting the leading edge of the pulse.

For analog video, CRT screens used a method called raster scanning,

which could scan from the top to bottom and back, up.

As it did this, the scan rate would create horizontal and vertical frequencies associated with the on-screen image.

Today we use these concepts but we also insert important information,

like audio and ancillary data during those blanking periods.

Here’s what a blanking period and active portion look like today.

That is all we care about right now.

Video data includes both the visual (or active) portion and the non-visual (or the blanking) portion.

There is both horizontal (H) and vertical portions (V) of data and we can determine the total,

active and blanking portions of both the horizontal and vertical using these equations below.

(Don’t worry, these won’t be on the test, just good information to know.)

TMDS (or for Transition Minimized Differential Signaling) carries the actual video, audio and infoframe data.

TMDS encodes the data using an eight to ten bit encoding algorithm,

so every eight bits of data we send ten bits (There's a little bit of overhead of 2 bits for every 10 bits sent.)

There are three channels (0, 1 and 2) used to send the TMDS data which aligns with R, G and B or Y, Cb and Cr.

The TMDS clock keeps everything in sync as it is sent across the wire.

Recall that we are still following what we did with analog video. There is an active region and a blanking region.

The active video Data region is the pixel data that is to be displayed on the sink.

The blanking region is used for control of the synchronization of the data between the horizontal and the vertical sync pulses.

Additionally in the blanking region there are Data Islands which contain either audio or infoframes.

By making use of essentially empty data

we are able to pack in audio and details about the video data being sent.

Both audio data and infoframes are sent during the horizontal and vertical blanking periods.

Audio data contains the audio packets, that is considered embedded audio.

There are a few different kinds of infoframes

but the one we're really concerned about is the AVI or the Auxiliary Video Information.

Similar to EDID the AVI infoframe provides the timing details.

However, this information is specific to the video and audio data being sent,

unlike EDID that provides multiple timings for ranges of values capable by the sink.

Here is a visual example of how the data is packed.

The visual portion is the darker gray area

and the data island containing audio and infoframes is the blue portion.

You can see those are placed in the blanking portion.

Let’s talk about DisplayPort!

DisplayPort was designed to be backwards-compatible with HDMI, DVI, and VGA,

supporting next-generation displays

while maintaining the compatibility with existing analog and digital displays.

Dual-mode DisplayPort interfaces are designed to transmit a single DVI or HDMI protocol

across the interface through the use of an adapter.

When it comes to the Q-SYS NV Series,

here’s a list of common resolutions and corresponding frame rates on the HDMI inputs.

NV Series can also scale to these resolutions and frame rates on the HDMI outputs.

That's right, you heard correctly, there are robust scalers built into every HDMI output in the NV Series.

For audio, the NV Series supports multiple input scaling frame rates and outputs them to 48 kHz.

Every HDMI input is capable of receiving and de-embedding 8 channels of LPCM audio

and every HDMI output is capable of sending and embedding audio up to 8 channels of LPCM.

And of course, all of that audio is fully Q-SYS routable, which means you can route to external loudspeakers,

or if you really want to get tricky

you can use a PA router to send pages directly to the display’s onboard loudspeakers.

Alright, we’re in the home stretch.

When you get back, we're gonna wrap up with a discussion of our video codec, Q-SYS Shift.

We'll see you in a bit.