6 ms·

Sending audio to LKV373 HDMI extenders (2021)

79 points by luu 3y ago

awehoiwaegw 3y ago
[dead]
rektide 3y ago
People are amazing. I love this. Adore it. A thread of various awesome enterprising hackers, searching for truth, and using observability & tools to uncover meaning. Then bend reality to their whims & desires. This is the best human spirit. It's a pity technology so often obstructs rather than builds this human mastery. Alas! Never-the-less, humanity persisted. Against the throws of corporate-controlled limiting tech. Break out that wireshark & conquer in the name of freedom! Become great! Be unbounded. I have huge respect for the Chromecast ecosystem, but there's so many weird prickly points for it. For a while I had a chromecast plugged in to a computer which then variously resent the output. This looks like a great way to do the same but simpler/dumber. One of the specific flaws of Chromecast is that if you stream a video, it can only go to a single device. Meaning my whole home audio does no good. Something like this could help me work-around that limitation. It's great how absurdly flexible these devices are, but it sucks enormous egg that Chromecast apps will only stream in the first place to signed Chromecast devices; this whole thing should be a non-issue I can software workaround. But a hardware workaround like this is adequate.
jaywalk 3y ago
I didn't even know HDMI extenders over IP existed! I wouldn't use it for TV/movies, because the re-compressed picture can't look all that great. But I could imagine plenty of uses for something like that!
- dylan604 3y ago
  Why do you assume the signal is being recompressed or in any other way manipulating the image?
  - duskwuff 3y ago
    Well, for one, the fact that it's streaming frames as motion JPEG...
    - dylan604 3y ago
      Where do you see that? I quickly glanced at the Amazon listing, and saw nothing about this. I could have glanced too quickly and missed it, but it just seems like a totally strange thing for it to do.
      - mrpippy 3y ago
        It’s in the article
  - monocasa 3y ago
    Because a 1080p60 video stream is about 3Gb/sec on the wire uncompressed like happens over HDMI. 1920w * 1080h * 3colorbytes * 8bits/byte * 60fps = 2,985,984,000 bits/sec.
    - dylan604 3y ago
      Okay, but the original signal is not RAW uncompressed either. It's just a serial signal, so converting that into IP packets is pretty much all I'm assuming this is doing and then converting those back to an HDMI formatted signal on the other end. The only thing different about this unit from others is that it's actually turning them into actual network traffic to connect to an existing network.
      - monocasa 3y ago
        > Okay, but the original signal is not RAW uncompressed either. HDMI is in fact the RAW color values, uncompressed. Each of the color channels are serial, but that doesn't really change anything about the raw bitrate.
        3y ago
- bobsmooth 3y ago
  You can do HDMI over a lot of things. They all work by encoding the video stream, usually h264, and sending it over the network. Check out HDBaseT which does video, ethernet, USB and power over a single cat5e cable.
- blahlabs 3y ago
  Not sure if you gave heard of NDI before? Its a broadcast quality low latency protocol for video/audio over 1Gb links
squarefoot 3y ago
There was some effort to reverse engineer those devices [1] so that one could use for example either transmitters or receivers paired with normal PCs and not just connecting them straight each other. There are also newer models around, though I'm not aware of any reverse engineering efforts so far. If you want to tinker with them, please leave some writeup of the results. Beware that there are both HDMI over IP and aesthetically very similar, but often cheaper, HDMI over Ethernet cable adapters. The 2nd ones contain no brain and can't do any IP encapsulation, they're essentially just level translators using CATx cable to carry the HDMI signals, and of course aren't compatible with any network devices, switches, etc. For that use, you want HDMI to IP transmitters and receivers, which should be clearly marked as capable of working in a network environment. Check carefully the features before buying, because some among the stupid level translators sold on the usual channels are marked as HDMI over IP, which they clearly are not. 1 - https://blog.danman.eu/reverse-engineering-lenkeng-hdmi-over-ip-extender/ https://blog.danman.eu/reverse-engineering-lenkeng-hdmi-over...
- comfypotato 3y ago
  Do you have any insight regarding latency? Intuitively it sounds like HDMI over Ethernet may actually be a tad faster. I’ve also seen HDMI over IP devices marketed specifically as low-latency. I’m asking because I’ve heard a gripe over the technology generally that it’s too high latency to play video games.
  - squarefoot 3y ago
    There's a short video on the page I linked showing figures around 100ms at 1080p, which seems quite good. The author however suggests newer models to achieve higher frame rates, but I have no knowledge of any reverse engineering wrt those models.
Hasz 3y ago
Wow, 100mS of latency? Surely most of that is in the encode/decode? For comparison, I see somewhere on the order of 1-10mS of latency streaming over sunlight/moonlight. That’s close enough to “live” to make it feel real. For watching movies, these are nifty tools, but sunlight/moonlight are a great combo for near-real-time control (ie video games)

79 points by luu 3y ago

[dead]

People are amazing. I love this. Adore it. A thread of various awesome enterprising hackers, searching for truth, and using observability & tools to uncover meaning. Then bend reality to their whims & desires. This is the best human spirit. It's a pity technology so often obstructs rather than builds this human mastery. Alas! Never-the-less, humanity persisted. Against the throws of corporate-controlled limiting tech. Break out that wireshark & conquer in the name of freedom! Become great! Be unbounded. I have huge respect for the Chromecast ecosystem, but there's so many weird prickly points for it. For a while I had a chromecast plugged in to a computer which then variously resent the output. This looks like a great way to do the same but simpler/dumber. One of the specific flaws of Chromecast is that if you stream a video, it can only go to a single device. Meaning my whole home audio does no good. Something like this could help me work-around that limitation. It's great how absurdly flexible these devices are, but it sucks enormous egg that Chromecast apps will only stream in the first place to signed Chromecast devices; this whole thing should be a non-issue I can software workaround. But a hardware workaround like this is adequate.

jaywalk 3y ago

I didn't even know HDMI extenders over IP existed! I wouldn't use it for TV/movies, because the re-compressed picture can't look all that great. But I could imagine plenty of uses for something like that!

dylan604 3y ago
Why do you assume the signal is being recompressed or in any other way manipulating the image?
- duskwuff 3y ago
  Well, for one, the fact that it's streaming frames as motion JPEG...
  - dylan604 3y ago
    Where do you see that? I quickly glanced at the Amazon listing, and saw nothing about this. I could have glanced too quickly and missed it, but it just seems like a totally strange thing for it to do.
    - mrpippy 3y ago
      It’s in the article
- monocasa 3y ago
  Because a 1080p60 video stream is about 3Gb/sec on the wire uncompressed like happens over HDMI. 1920w * 1080h * 3colorbytes * 8bits/byte * 60fps = 2,985,984,000 bits/sec.
  - dylan604 3y ago
    Okay, but the original signal is not RAW uncompressed either. It's just a serial signal, so converting that into IP packets is pretty much all I'm assuming this is doing and then converting those back to an HDMI formatted signal on the other end. The only thing different about this unit from others is that it's actually turning them into actual network traffic to connect to an existing network.
    - monocasa 3y ago
      > Okay, but the original signal is not RAW uncompressed either. HDMI is in fact the RAW color values, uncompressed. Each of the color channels are serial, but that doesn't really change anything about the raw bitrate.
      - 3y ago
bobsmooth 3y ago
You can do HDMI over a lot of things. They all work by encoding the video stream, usually h264, and sending it over the network. Check out HDBaseT which does video, ethernet, USB and power over a single cat5e cable.
blahlabs 3y ago
Not sure if you gave heard of NDI before? Its a broadcast quality low latency protocol for video/audio over 1Gb links

squarefoot 3y ago

There was some effort to reverse engineer those devices [1] so that one could use for example either transmitters or receivers paired with normal PCs and not just connecting them straight each other. There are also newer models around, though I'm not aware of any reverse engineering efforts so far. If you want to tinker with them, please leave some writeup of the results. Beware that there are both HDMI over IP and aesthetically very similar, but often cheaper, HDMI over Ethernet cable adapters. The 2nd ones contain no brain and can't do any IP encapsulation, they're essentially just level translators using CATx cable to carry the HDMI signals, and of course aren't compatible with any network devices, switches, etc. For that use, you want HDMI to IP transmitters and receivers, which should be clearly marked as capable of working in a network environment. Check carefully the features before buying, because some among the stupid level translators sold on the usual channels are marked as HDMI over IP, which they clearly are not. 1 - https://blog.danman.eu/reverse-engineering-lenkeng-hdmi-over-ip-extender/ https://blog.danman.eu/reverse-engineering-lenkeng-hdmi-over...

comfypotato 3y ago
Do you have any insight regarding latency? Intuitively it sounds like HDMI over Ethernet may actually be a tad faster. I’ve also seen HDMI over IP devices marketed specifically as low-latency. I’m asking because I’ve heard a gripe over the technology generally that it’s too high latency to play video games.
- squarefoot 3y ago
  There's a short video on the page I linked showing figures around 100ms at 1080p, which seems quite good. The author however suggests newer models to achieve higher frame rates, but I have no knowledge of any reverse engineering wrt those models.

Hasz 3y ago

Wow, 100mS of latency? Surely most of that is in the encode/decode? For comparison, I see somewhere on the order of 1-10mS of latency streaming over sunlight/moonlight. That’s close enough to “live” to make it feel real. For watching movies, these are nifty tools, but sunlight/moonlight are a great combo for near-real-time control (ie video games)