Video Transcript
Advanced Digital Video Part 3)
5m 6s
00:07
Welcome back.
00:08
We’ll turn on the Wayback Machine and go all the way back to analog video.
00:13
In an analog video image, you have different portions of video: active, sync, front porch and back porch.
00:22
Most importantly, the pulse sync is a feature that is used to keep the synchronization.
00:27
Video receivers and displays look for the sync pulse by detecting the leading edge of the pulse.
00:33
For analog video, CRT screens used a method called raster scanning,
00:38
which could scan from the top to bottom and back, up.
00:42
As it did this, the scan rate would create horizontal and vertical frequencies associated with the on-screen image.
00:49
Today we use these concepts but we also insert important information,
00:53
like audio and ancillary data during those blanking periods.
00:58
Here’s what a blanking period and active portion look like today.
01:02
That is all we care about right now.
01:04
Video data includes both the visual (or active) portion and the non-visual (or the blanking) portion.
01:11
There is both horizontal (H) and vertical portions (V) of data and we can determine the total,
01:17
active and blanking portions of both the horizontal and vertical using these equations below.
01:24
(Don’t worry, these won’t be on the test, just good information to know.)
01:28
TMDS (or for Transition Minimized Differential Signaling) carries the actual video, audio and infoframe data.
01:37
TMDS encodes the data using an eight to ten bit encoding algorithm,
01:43
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.)
01:51
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.
02:02
The TMDS clock keeps everything in sync as it is sent across the wire.
02:07
Recall that we are still following what we did with analog video. There is an active region and a blanking region.
02:13
The active video Data region is the pixel data that is to be displayed on the sink.
02:18
The blanking region is used for control of the synchronization of the data between the horizontal and the vertical sync pulses.
02:25
Additionally in the blanking region there are Data Islands which contain either audio or infoframes.
02:32
By making use of essentially empty data
02:35
we are able to pack in audio and details about the video data being sent.
02:39
Both audio data and infoframes are sent during the horizontal and vertical blanking periods.
02:45
Audio data contains the audio packets, that is considered embedded audio.
02:50
There are a few different kinds of infoframes
02:53
but the one we're really concerned about is the AVI or the Auxiliary Video Information.
03:00
Similar to EDID the AVI infoframe provides the timing details.
03:05
However, this information is specific to the video and audio data being sent,
03:10
unlike EDID that provides multiple timings for ranges of values capable by the sink.
03:16
Here is a visual example of how the data is packed.
03:19
The visual portion is the darker gray area
03:22
and the data island containing audio and infoframes is the blue portion.
03:27
You can see those are placed in the blanking portion.
03:30
Let’s talk about DisplayPort!
03:33
DisplayPort was designed to be backwards-compatible with HDMI, DVI, and VGA,
03:38
supporting next-generation displays
03:41
while maintaining the compatibility with existing analog and digital displays.
03:46
Dual-mode DisplayPort interfaces are designed to transmit a single DVI or HDMI protocol
03:53
across the interface through the use of an adapter.
03:55
When it comes to the Q-SYS NV Series,
03:58
here’s a list of common resolutions and corresponding frame rates on the HDMI inputs.
04:04
NV Series can also scale to these resolutions and frame rates on the HDMI outputs.
04:09
That's right, you heard correctly, there are robust scalers built into every HDMI output in the NV Series.
04:17
For audio, the NV Series supports multiple input scaling frame rates and outputs them to 48 kHz.
04:25
Every HDMI input is capable of receiving and de-embedding 8 channels of LPCM audio
04:32
and every HDMI output is capable of sending and embedding audio up to 8 channels of LPCM.
04:40
And of course, all of that audio is fully Q-SYS routable, which means you can route to external loudspeakers,
04:46
or if you really want to get tricky
04:49
you can use a PA router to send pages directly to the display’s onboard loudspeakers.
04:54
Alright, we’re in the home stretch.
04:56
When you get back, we're gonna wrap up with a discussion of our video codec, Q-SYS Shift.
05:01
We'll see you in a bit.
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Advanced Digital Video Part 3)
5m 6s