Author Topic: "Rec signal" for external recorder on replay  (Read 5029 times)

mkonrad

  • Newbie
  • *
  • Posts: 13
    • View Profile
"Rec signal" for external recorder on replay
« on: January 27, 2022, 12:28:27 PM »
I am waiting for the delivery of my Chronos 2.1

To be able to replay multiple clips to clients and display images on SDI monitors I will connect the Chronos via HDMI to an external recorder. The recorder (Blackmagic Video assist 12G) cross converts the HDMI to SDI.

I will record a proxy clip on the Video Assist of each Chronos replay so I can go back to shots that have been saved and are no longer on the Chonos (as I surly have agency or clients ask me to replay a previous clip to compare/choose/validate a shot).

I knor the Atomos and Blackmagic recorders have settings for numerous cameras to Auto record once I hit the record button on standard Canon/Nikon/Fuji/Sony cameras.

Does anyone know what type of signal the cameras send to communicate with the recorder?
Is there a way to code a solution to send the signal "on replay" so I do not forget to manually hit record every time I replay a clip?

Nikon1

  • Hero Member
  • *****
  • Posts: 983
    • View Profile
Re: "Rec signal" for external recorder on replay
« Reply #1 on: January 27, 2022, 12:48:00 PM »
Not having worked with camera Control/ Interactive Link between External Recorders and such to Cameras myself, i just had a look at the Z-Cam, cause i know that one would need to do that.
 https://www.slashcam.com/news/single/Atomos-Ninja-V-Firmware-Update-ermoeglicht-ProRes-R-15954.html
 Given that it is apparently unable to communicate with the Camera when RAW is Recorded, which obviously should use way more Bandwidth than standard HDMI, i guess they are just using some kind of Ethernet Capability of the HDMI Standard here; not only to do the Communication back to the Camera, but also to Push the Additional Data for RAW Format here back and Forth. In case of RAW Recording that "spare Bandwidth" the HDMI does not take up will be used for Image data, so it wont work there.
 https://en.wikipedia.org/wiki/HDMI#HDMI_Ethernet_and_Audio_Return_Channel
 I however highly doubt, that anything this in depth about the HDMI Standard or the Communication Protocol used here would be fully Public (have not spent more than 2 Minutes Looking tbf., so it might, but i dont think so. Its just like Camera Lens Mounts and such, usually you need to Buy the Full Specification and Documentation and sign an NDA to not make it Publicly available in any Capacity, Maybe even also a License to use it if for a commercial Product.).
 .
 Your best Bet would Probably be to figure out, if you can somehow get hold of Blackmagic or Atomos Customer Support, ideally an Actual Person to directly Speak to, and ask them on how to do that. Othewise (if you cant find any more info online), your only other option would most likely be to find a way to extract and Analyze the Ethernet part of the Signal that is going on with these Recorders and Reverse-Engineer that, however one would do that (more of a Hardware Guy myself, i try to avoid coding and Signal Processing stuff if i can...).
 .
 But in Short, Probably some Kind of Ethernet signal.
 Might not even be super Complicated, should just be some sort of command/ Status update the Camera gives out via HDMI if i understand correctly how that would work for start Recording on Record Button press at the Camera.
« Last Edit: January 27, 2022, 12:53:05 PM by Nikon1 »

Nikon1

  • Hero Member
  • *****
  • Posts: 983
    • View Profile
Re: "Rec signal" for external recorder on replay
« Reply #2 on: January 27, 2022, 01:22:36 PM »
Did search a bit more, but only thing more i could figure out for now, is that it is more or less "Standard Ethernet" for the Most part it seems, but somehow just using Pin 14 and 19 of the HDMI (cant quite Wrap my head around how that would work, but probably something like these Early Ethernet Standards that would only need a Single Pair of Wires and could use Connectors like BNC or Straight up Unshielded, twisted Telephone Wire for the Lower Speeds), so a Memory Oscilloscope on those two Pins and some guy that knows to decipher Binary Stuff should get you mostly to the Point where you could figure out what kind of signal (/signal-chain) the External Recorder Expects to Start (/Stop) Recording.
 HDMI seems to have somewhat of an "startup Sequence", which i guess you still also would need to pay some attention to, if you do a custom solution like this, Pin 19 seems to be used to figure out if something got connected as well, so you most likely cant just remove them from the Cable to feed some external Signal into from elsewhere.
 Found some Sony Patents, which show a bit of what is going on when Connecting / Disconnecting the HDMI Port to a Device and all the Data/ Communication that is Expected to verify its Connected to a Valid Device.
 https://patents.google.com/patent/US20110206355A1/en
 https://patents.google.com/patent/EP2405654A1/en
 Maybe these will help a bit with your Project.
 

mkonrad

  • Newbie
  • *
  • Posts: 13
    • View Profile
Re: "Rec signal" for external recorder on replay
« Reply #3 on: January 28, 2022, 07:55:21 AM »
I posted a request on the Software development forum over on the Blackmagic site (who make one of the recorders)

A "timecode trigger" would auto start recording, but its usual use of syncronising the record of a 1000fps camera and a 60fps recorder does not make much sense to evaluate clips.

If the timecode trigger signal could be send "on replay" at the set in and out points it would be possible to automate the external recording
which would make the camera a lot easier to inegrate in a setup with directors, agencies and clients

any software geeks who could enable this or point me in the right direction?
I am a user/DOP and not a software developer...