Video Transcript
Advanced Digital Video (Part 2)
9m 56s
00:07
Usually when you're troubleshooting digital video, it’s usually not because of the actual video data,
00:13
but the ancillary video tech like these that come along with it.
00:18
These provide communications between the source, sink (display/endpoint device) and repeater devices.
00:26
This is a very valuable slide. I would take a screen shot of this if I were you.
00:31
At a very high level, this shows the handshake process that takes place when you connect two HDMI devices.
00:38
If you learn nothing else during this presentation besides this one slide it will have been time well spent
00:44
and should really help you during your troubleshooting sessions with digital video.
00:48
First our source sends a +5V,
00:51
a sink interprets that as a connected source and in turn sends a Hot Plug Detect response.
00:59
You often hear about “hot plugging” a source or sink which means removing and reseating the HDMI cable,
01:05
and basically restarting the whole HMDI handshake process.
01:09
Once the source receives the HPD, it will then request EDID, and then the sink will respond with the EDID data.
01:18
At this point one of two things will happen: if the source is HDCP compliant it will send an HDCP request.
01:26
If the source is not HDCP compliant, then the source will start delivering unencrypted video via TMDS.
01:34
If the source is HDCP capable and has sent an HDCP request then it will perform the HDCP negotiation
01:42
and if everything goes well as planned it will begin to encrypt that video data as needed.
01:47
The video timing sent by the source is determined through reading the sink’s EDID
01:52
and sending video data compatible with the sink EDID.
01:55
Let’s talk about DDC, or Display Data Channel.
02:00
This is an older technology that uses an I2C technology bus.
02:05
An I2C bus consists of three wires: SDA (which is data), SCL (which is clock), and a logic "high" DC pull voltage.
02:16
For the DDC, the logic "high" voltage is specified to be +5V.
02:22
The DDC specifications define a +5V supply connection for the source to provide the power
02:28
to a display's EDID circuitry so that communication can be enabled, even if the display is powered off.
02:34
Here's where you see the HDMI connector where theDDC is. Pin 15 is for the SCL
02:41
and pin 16 is for the SDA.
02:43
EDID (or extended display identification data) allows the sink to tell the source what it can and can't do.
02:50
A display basically says “I support these resolutions and frame rates” …
02:54
and then the source will send appropriate video data based on the EDID it reads over the DDC.
03:00
The EDID carries the preferred resolution, which is typically what the source will output.
03:06
EDID started out with VGA, and then moved on to DVI, HDMI, and Display Port.
03:12
It was developed by VESA, and it's transmitted today over at the E-DDC, but we still just call it DDC.
03:19
There are EDID standards, structure, and data blocks.
03:23
When speaking about EDID is good to keep these in mind to help from getting confused.
03:27
Here’s a quick look at the EDID standards available today.
03:31
With structure, we still mainly use 1.3 but some 1.4 structures are starting to appear.
03:38
Blocks are what actually contains EDID information.
03:41
The primary data block 0 is always required, and one or more extension blocks might exists as well.
03:48
Most commonly found extension block is the CTA-861,
03:54
which supports advanced capabilities of consumer devices that incorporate HDMI.
03:59
Data block 0 is where we find the preferred timing and other characteristics of the sink
04:05
and if there are extension blocks that's where we'd look.
04:08
Now there are many extension blocks supported in EDID but the CTA-861 extension block,
04:13
which is shown here, is almost always available in most HDMI sinks.
04:18
It contains additional sink characteristics not already defined in the primary block 0.
04:24
As we have learned, EDID is read from sink, display or projector.
04:28
It identifies connection type, supported resolutions, its preferred resolution,
04:33
supported audio and color space information.
04:36
Based on reading EDID,
04:38
a source or repeater device knows what to send and will format its video data appropriately.
04:43
Our Q-SYS NV Series also does some intelligent EDID filtering so connected sources
04:49
don’t send any video data that is not supported on this device.
04:54
This ensures that if the device EDID is copied and used on any HDMI input in the Q-SYS Design
05:00
it will be 100% compatible with NV Series devices.
05:04
For example, we accept up to eight channels of LPCM audio on any HDMI input but we don't currently
05:11
accept Dolby or DTS encoded audio.
05:15
In this case, we remove the support for Dolby,
05:18
DTS and any other forms of bitstream audio and only list up to 8 channels of LPCM audio.
05:25
Next is DRM, which stands for Digital Rights Management.
05:29
And more specifically, when we talk about DRM we're usually talking about HDCP.
05:34
HDCP protects the intellectual property of the creators, making it harder to copy or steal that content.
05:41
For better or for worse, HDCP is here to stay, so let’s do our best to understand it.
05:48
This video encryption process uses three steps: authentication, encryption and key renewal.
05:55
A source device initiates an authorization handshake protocol using keys and encrypted messages
06:02
to determine if a connected device is authorized and able to receive encrypted content.
06:07
All downstream devices must be authorized for encrypted content.
06:11
Once the source device has determined that all downstream devices
06:15
are HDCP compliant and the maximum number of devices has not been violated,
06:20
encrypted content is then sent to all downstream devices.
06:24
Encryption keys are periodically updated while devices are connected and sending content.
06:29
Secret keys are used during the encryption process,
06:32
so if those secret keys are compromised the whole system can be circumvented.
06:37
All compromised keys are revoked and the revoked list compared against any downstream devices
06:43
to verify only legitimate public keys are used.
06:47
Let's be honest, HDCP is often the root of significant issues in transporting digital video.
06:53
Sometimes when it is not needed, it might be worth turning it off.
06:58
That's why we added that feature to the NV-32-H.
07:01
On the HDMI inputs of each of these devices, you're able to disable HDCP.
07:07
Recall, HDCP doesn't just apply to HDMI but it is also valid on other interfaces.
07:13
It is transmitted over the DDC, same as EDID.
07:17
HDCP was designed to prevent content from being played or recorded on unauthorized devices.
07:23
Therefore, all authorized devices must obtain a license, pay annual fee and submit to certain conditions.
07:30
Here is a brief timeline of HDCP.
07:33
As you can see, more interfaces began to adopt the protocol as time goes by.
07:38
But … you might be asking "why do you care about these versions?"
07:42
Well, for starters, version 2.2 is not backwards compatible with version 1.4.
07:49
HDCP 1.4 is typical for HD content and HDCP 2.2 is typical for 4K content.
07:58
Since they are not backwards compatible between 2.2 and 1.4,
08:02
manufacturers need to build devices that support both 1.4 and 2.2.
08:08
There are three types of devices in the HDCP link: the source, the sink and the repeater.
08:13
Now, the source and the sink are pretty self-explanatory.
08:17
However the Repeater accepts content, decrypts it, and then re-encrypts and retransmits the data.
08:25
Repeaters have HDMI inputs and outputs.
08:28
Which is another reason why we care about HDCP versions - it's the device count limitation
08:34
As you can see, HDCP 1.4 allows more devices in in the chain than 2.2. 7 levels of repeaters versus 4.
08:44
In general HDMI 1.4 is likely to be used with HDCP 1.4, and HDMI 2.0 is likely to be used with HDCP 2.2.
08:55
However, some HDMI 1.4 (HD) devices may support HDCP 1.4 or 2.2
09:05
and some HDMI 2.0 (4K) devices may support HDCP 1.4 or 2.2.
09:12
Remember this slide? Well, it’s back!
09:15
Let's recall that the source will send +5V, the sink will respond to the HPD event,
09:22
the source requests the EDID, and the EDID is sent to the source,
09:27
then the HDCP is then negotiate and the video data is sent encrypted or unencrypted.
09:33
CEC is not necessarily part of the handshake or hotplug process,
09:38
but it is an additional bidirectional ancillary data channel for device control over HDMI.
09:45
Okay, let's step away from your computer, let your eyes uncross, go get some fresh air,
09:51
and we'll come back whenever you're ready.
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Advanced Digital Video (Part 2)
9m 56s