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bjustice  
#1 Posted : Tuesday, December 4, 2018 9:44:15 AM(UTC)
bjustice

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Hello everyone!

Disclaimer: I am an aerospace engineer and am out of my element here. Nonetheless, I need find a solution that will meet the following requirements:
- Record 30 3G-SDI streams
- all streams at 1080p60
- Only need to record for 500 seconds intervals
- Need to encode/save as MPEG-2 format

Here are my collected thoughts so far:

- Use VMIX multicorder software.
- Build 2 machines. Each machine will be responsible for recording up to 16 channels each
- Use BlackMagic Decklink Quad 2 capture cards. (2 cards per machine)
- Use BlackMagic MPEG-2 codec. (My vague understanding is that the capture cards perform the encoding rather than GPU or CPU?)
- Each capture card needs 8 gen2 PCIE lanes, so I need 16 PCIE lanes to CPU for each machine solely for these cards
- Use 2 Samsung Evo 960 NVMe in RAID 0 format. This will consume 4 PCIE lanes each. (If each stream consumes 100Mbits/second, then that's 1.6Gbits/second of required write speed to hard drive)
- motherboard/CPU with atleast 4 full PCIE slots with 8 dedicated PCIe lanes to each slot. (I haven't picked a board or CPU yet.)
- 32GB DDR4 RAM

Again, I only have a vague understanding of what I'm doing. I have a list of things that I don't quite understand yet:

- My understanding is that the BlackMagic capture cards have onboard FPGA that will encode the SDI input into MPEG-2 without having to pass the uncompressed video through the GPU or CPU. Is this true, or am I incorrect?
- My understanding is that the capture card will push the encoded MPEG-2 video to the CPU which then reroutes to the SSDs. As such, I shouldn't need very much GPU. Rather, I simply need to make sure that CPU can handle the PCIe lane number
- My understanding is that I can RAID 0 multiple SSDs in order to increase my write-rate. Looking at the numbers, it seems that two Samsung Evo 960 NVMEs at a write rate of 1900MB/s each should be plenty.

Any feedback on these thoughts would be greatly appreciated. It has been oddly difficult to find other people building similar machines.
Thanks for any input/thoughts!
IceStream  
#2 Posted : Tuesday, December 4, 2018 12:57:44 PM(UTC)
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@ bjustice





I'm not saying it's impossible, but you might need more than two machines...
Just my thoughts.


Ice
bjustice  
#3 Posted : Tuesday, December 4, 2018 1:54:51 PM(UTC)
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haha, it's very possible. And more machines is fine. But, ultimately, I guess that I don't have a good understanding of what resources that I need in order to capture/encode/record SDI video.

And I'm pretty fuzzy on what resources are available on the capture card FPGA. Can the capture card perform embedded encoding, or am I forced to push the video through the GPU for encoding?
bjustice  
#4 Posted : Tuesday, December 4, 2018 2:06:23 PM(UTC)
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So far, this thread has been the most insightful:
https://forums.vmix.com/...aspx?g=posts&m=57091

This thread seems to indicate that:
- capturing 16 SDI streams at 1080p50 is within grasp of a modest machine. Maybe ~$10k
- The encoder settings will determine how much GPU is used. (This indicates to me that the video has to be passed though the GPU for encoding. I'm still curious if there are any encoder options that can be performed directly on the capture card FPGA without involving the GPU.)
- NDI/IP streams consume a ton of CPU resources in order to decode/record. As such, it's much better for me to try to perform all recording using SDI streams into capture cards.
zenvideo  
#5 Posted : Tuesday, December 4, 2018 6:27:16 PM(UTC)
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I know this is a vMix forum, but software-wise you might be better off looking at something like Metus Ingest which is a dedicated multi-channel video recording application with lots of codec options, assuming you haven't seen it already.
bjustice  
#6 Posted : Wednesday, December 5, 2018 4:57:42 AM(UTC)
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I have not seen Metus-Ingest. This seems like an interesting option.
Here is their hardware requirements page:
https://metuskb.atlassia...equirements+-+The+Latest

"The hardware requirement of Metus Ingest depends on many variables, such as number of inputs, target format, frame rate etc…
Please contact our sales team for Ingest hardware recommendation that would meet your need."

So, I'll contact them and see what they suggest
JoseL  
#7 Posted : Wednesday, December 5, 2018 6:31:41 AM(UTC)
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Metus for 30 cameras?, really?, only licenses will be more expensive than hardware. I think vmix is more eficient than metus, at least with mp4.
I didn’t test mpeg2, but mp4 with p5000 is near limit or maybe over limit with 16 sdi3g inputs.
I think the best way is 3 machines. No problem to get 10x sdi 3g with p5000 to mp4. But i didn’t test mpeg2.
bjustice  
#8 Posted : Sunday, March 17, 2019 3:34:38 PM(UTC)
bjustice

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Update:

As you have all pointed out, I was very naive of the computing requirements for handling even a single 3G-SDI stream at 1080p 60fps.

We're landing on a solution where we will have multiple video recording machines where each machine is built to record 8 streams of 3G-SDI. A single machine build has specs that roughly look like this:
- 2U form factor
- 2 Samsung Evo 970 Pro NVME 1TB (formatted as individual drives where VMIX writes 4 video streams to one drive, and 4 video streams to the other)
- low-end GPU that supports DirectX 10 (We're not planning any hardware accelerated encoding, and we're truly only interested in VMIX for multicorder)
- Intel Xeon processor. We're thinking something around 16 cores @ 2.6 GHz as the minimum spec
- BlackMagic Decklink Quad2 capture card

We're planning to recording directly to YUV 4:2:2 uncompressed format. Quite simply, the CPU requirements for real-time transcoding are insane. I had no idea that this was the case. The uncompressed codec uses very little CPU and ensures that I don't drop any frames. The Samsung Evos (thank god M.2 technology is here) handles the massive write speed of all of this uncompressed data. At 8 streams of 3G-SDI, this yields around 120GB/s of data being written to disk. The Evos (1 TB each) then give me about 16 minutes of recording time assuming an empty disk. Plenty for my purposes.

Post-recording transcoding can then happen with Handbrake and I'm a happy camper. Handbrake is amazingly fast it seems.

So, for anybody who finds this post in the future, beware that 1080p 60fps is a beast, and real-time software based transcoding is not where I would have expected for it to be at this day in age. And I also idly wonder why there aren't capture cards on the market that are able to acquire raw 3G-SDI and encode to H.264 on enbedded FPGAs and then stream the H.264 to the computer as the "captured video." Maybe these do exist and I didn't find it. Who knows.
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