Recording HDMI - Page 1
Forum section: electronics / projects

author: Jan Audio
author_rank: Frequent Contributor
timestamp: June 21, 2020, 11:10:52 am
content: Hi, i was talking to someone who bought a box to use for recording HDMI.Some special box he need for streaming for twitch so people can watch him play games.I think he got ripped off, it is not allowed to sell a device that can record HDMI or am i wrong ?There are no HDMI video recorders in any shop.What chip do you need to make a simple HDMI recorder to SD card ?I bet a PIC32 in DIP can not handle it as usual.What do you think about it, does he got ripped off for 500 ?, is twitch selling these devices maybe indirect ?I have the feeling he wont be earning his money back.

author: ebclr
author_rank: Super Contributor
timestamp: June 21, 2020, 11:56:32 am
content: HDMI can be recorded if not HDCP involved,https://pt.aliexpress.com/item/4001019854432.html?spm=a2g0o.productlist.0.0.2ccd6d90zkRjAw&algo_pvid=9886697e-672c-4254-9e27-791bb36978d6&algo_expid=9886697e-672c-4254-9e27-791bb36978d6-5&btsid=0ab50a5715927404221081543ee6b8&ws_ab_test=searchweb0_0,searchweb201602_,searchweb201603_

author: NiHaoMike
author_rank: Super Contributor
timestamp: June 21, 2020, 02:27:33 pm
content: A LKV373A is about $30 for 1080p capture. Add about $10 for a splitter that defeats HDCP. Or about $40 for a splitter that can downscale 4K if he wants to play at 4K but stream at 1080p.4K capture is a lot more expensive.

author: DaJMasta
author_rank: Super Contributor
timestamp: June 21, 2020, 03:21:47 pm
content: HDCP stripping exists and can be bought, perhaps more doubiously, but as commercial products. HDMI recording without HDCP can be done fine, legally - I've got a ~$75 box that let's me do 1080p60 capture for my digital microscope and it works great.As for what you need - single chip solutions to capture exist, but a regular SD card isn't going to be able to keep up with the bandwidth. To store it, you'd need an encoder of some sort, then still a pretty fast storage medium. By no means impossible, but much easier to do not as a standalone where you can just send all that data to a device that can process it without issue.Capture cards are essential for the broadcasting industry now - and that's not just for streamers - so there is a large market for them and especially if they have 4k60 capability or multiple inputs, $500 or more could be quite justified.

author: NiHaoMike
author_rank: Super Contributor
timestamp: June 22, 2020, 02:58:06 am
content: I have bought two HDMI splitters that happen to strip HDCP out of the box. One of those I bought with the intent of hacking it into a HDCP stripper after I read an article about it, the other I bought for the audio extraction feature. Not sure if I'll ever take advantage of the HDCP stripping feature since I boycott DRM in the first place, but it's ready if I ever find the need for it.The LKV373A has a H.264 encoder built in. That's usually a plus, but for some applications like performing machine vision on the HDMI signal, that gets in the way and there are USB 3.0 capture adapters that deliver an uncompressed capture.

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: June 22, 2020, 06:05:50 am
content: Your friend probably did not get ripped off (ripped off in the sense that someone sold him a cheap product for a lot of money. I'm not gonna comment on if he needs such a device - clarification later).Quote from: Jan Audio on June 21, 2020, 11:10:52 amIt is impossible, even for the best engineers on the planet, to use any off-the-shelfgeneral purposemicrocontroller to do HDMI capture (unless you get some special one that happens to have HDMI transceivers in it though I don't know if those exist).Why? It's quite simple really: like most video interfaces, HDMI is uncompressed. The 'transmitting device' uncompresses the video stream and then sends this over the cable. As a result, HDMI has quite high data-rates, together with other video interfaces, is likely (by a good margin) the fastest digital link through a cable in a consumer house. My 10 Gbit/s Ethernet can't hold a candle to the near 50 Gbit/s that the HDMI2.1 ports in my TV can handle.HDMI1 has three channels. Each of these sends data at a maximum rate of 1.65 GBit/s. (for a total signal rate of 4.95 GBit/s, however, the net data-rate is only 3.96 GBit/s due to the 8b10b coding). There is no way any microcontroller or even most microprocessors that don't have specific HDMI transceivers can handle this. This is why most capture cards use either a HDMI-specific IC, or an FPGA (which has high-speed SERDES) to handle this.This also brings us to the second problem:Quote from: Jan Audio on June 21, 2020, 11:10:52 amLets have a look at SD cards: The second-fastest spec is the 'UHS-III' transferrate, which (on paper) can do 624 MB/s. Spoiler: there exist no cards that can actually sustain that datarate. V90 cards are the fastest, and that '90' is for '90 MByte/s sustained write speed' (which is 720 Mbit/s). So, we can't just take the data of the HDMI stream, and somehow dump it into SD card. The SD card just can't keep up. This is why high-end cinema cameras record to SSDs. (and even then they use (possibly lossless) compression first).Most capture cards fall into three categories:1) Low-quality compression based on some HDMI receiver IC and then a microprocessor or an ASIC (not that familiar with this market, to be honest but with streaming becoming so common, there is really a new market for these ASICs)2) CPU-based compression: just act as an HDMI translation layer, stream it to a internal bus like PCIe, thunderbolt, and then use the CPU of the system to compress (I think a lot of modern CPUs/GPUs also come with H264/H265 hardware compression integrated).3) High-quality compression based on an ASIC or FPGA implementation. These do high-bit-rate H264 or H265 or similar compression on-the-go. This is what a lot of the higher-end cards do that are used in media. These solutions range from hundreds of dollars to tens-of-thousands for entire live-broadcast multi-camera high-speed recording setups that can record 20 or more 4k60fps streams at the same time.The gap between type 1 and type 3 is closing (or rather, you can now find affordable options that can do good-enough-for-most-applications compression). Broadcast will still demand more of their cards, and higher control over the compression.I have to say that I can find HDMI recorders in the local larger computer/electronics stores.

author: Jan Audio
author_rank: Frequent Contributor
timestamp: June 22, 2020, 02:43:39 pm
content: Understood, thanks all.So many pixels, top technology.Starting to have more respect for my TV.

author: Larryc001
author_rank: Regular Contributor
timestamp: June 23, 2020, 02:58:37 am
content: Would something like this not work?https://www.amazon.ca/AVerMedia-EzRecorder-Definition-Recording-ER130/dp/B00LAP3GC8

author: DaJMasta
author_rank: Super Contributor
timestamp: June 23, 2020, 03:00:36 am
content: Quote from: Jan Audio on June 22, 2020, 02:43:39 pmIt is really impressive what they can cram into a specialized single chip solution these days. If you look at the early 1080p+ TV designs you sometimes find stacks of FPGAs on multiple processing boards just to keep up!

author: Nerull
author_rank: Frequent Contributor
timestamp: June 23, 2020, 04:18:58 am
content: QuoteI picked one up at Best Buy a couple months ago. Couldn't find a webcam within 500 miles and the next best option was to hook up my Canon 5D. Always have the best video quality in the meeting....