What is a failover loopback ?
On-the-fly video processing applications take a live video signal in, perform some computing on it, and forward the modified live signal to next downstream equipment.
This kind of equipment performs live color correction, overlays, video mixing, keying, logo insertion, or any other form of video enhancement.
As the video processor is directly involved in the video signal path, it must be fault tolerant, and it must preserve the video signal in a variety of error cases.
This is why several DELTACAST video I/O card models – especially those that implement a hardware keyer – include failover loopback solutions.
A failover loopback, once triggered, bypasses the hardware or software processing and establishes a direct connection between the video input and the video output.
Several error conditions may require a failover loopback :
- Software crashes
- System failures
- Power outages
- Security breaches
- Maintained video loop during system start or after system shutdown
- Hardware defect
- ...
Loopback solutions
The different models of DELTACAST I/O cards with hardware keyer implement one or several of these failover solutions :
Bypass relays
Bypass relays, also named passive loopback or mechanical failover, is a hardware solution designed to switch between a state where video input and output signals are connected to the onboard processing unit (FPGA), and a state where the video input and output are electrically connected with each other to create a loop.
Bypass relays constitute an absolute failover against most cases of failure, including a loss of power supply. However, as the switch is made at electrical level, it results in a short signal break while operated.
Click on the video below to see the bypass relays in action during a surgical procedure involving live video processing.
Firmware loopback
Firmware loopback, also named active loopback or electronic failover, is a failover solution programmed in the onboard FPGA firmware. Being implemented within the same source code as video reception and transmission channels logic, the firmware loopback can be operated synchronously with the video, producing glitch-free switches.
Firmware loopback constitute a neat and flexible loopback solution, however it requires the FPGA to be powered up, and hence cannot be used as a failover solution in case of power outage.
DELTA-12G-ELP-KEY 11 active loopback
Note that, besides the standard failover solutions based on passive and active (firmware) loopback switching, the very specific DELTA-12G-elp-key 11 hardware keyer card features a third type of failover implemented at electronic level around the SDI reception and transmission chips. We call it active loopback in the VideoMaster SDK and documentation.
The DELTA-12G-elp-key 11 active loopback needs the card to be powered up to maintain the RX-TX loop but, unlike the firmware loopback solution, it does not require the FPGA firmware to be running. That failover mechanism hence provides additional protection against bricked or corrupted firmware situations.
Capture of the incoming signal is still possible while the active loopback loops the RX signal to the TX output of the card.
Summary of failover solutions
| Bypass relays | Firmware loopback | DELTA-12G-elp-key 11 active loopback | |
| Manual control through API | YES | YES | YES |
| Loop when software watchdog triggers | YES | YES | YES |
| Loop when FPGA fails | YES | ||
| Loop in case of power outage | YES | ||
| Seamless video switch | YES | YES | |
| Allows capture while in loop | YES | YES |
