Blackmagic Forum

I'm trying to find a way to trigger start/stop recording on a SoundDevices MixPre-3 II from a HyperDeck Studio Mini Ultra HD.

I've tried setting setting the MixPre to start/stop recording via HDMI, and fed HDMI from the HyperDeck into the MixPre, but that doesn't work.

I provide timecode to the HyperDeck (TC into an ATEM 2 M/E, then SDI to the HyperDeck, and TC goes with it) and also send TC to the MixPre via the aux-in, so I tried changing the MixPre to get timecode over HDMI from the HyperDeck, but it doesn't receive it — which tells me that the HyperDeck probably isn't sending out timecode over its HDMI, even though it's receiving it over SDI, which is probably why there's no start/stop command coming over HDMI either.

I trigger my HyperDecks using Bitfocus Companion, however no one engineering modules for Companion has figured out how to trigger a MixPre from there, so that options is out.

(Github thread on that topic if you're interested) https://github.com/bitfocus/companion-module-requests/issues/190

I'm out of ideas and open to suggestion. Any way to trigger a MixPre to start/stop recording when a HyperDeck starts and stops?

cheers
-Joseph

I don't think the original HyperDeck Studio Mini supported HDMI timecode output, and I'm not sure whether the updated HyperDeck models support this or not either. And even for the SDI start/stop record flags, I don't know that the HyperDeck actually generated these flags on its SDI outputs when pressing the HyperDeck record button (or triggering HyperDeck recording via the Ethernet control protocol).

I think it should be possible to get the HyperDeck to include timecode in its SDI outputs (if the Timecode Output setting is turned on). And then if you extract the timecode from the Hyperdeck SDI output (with something like a Teranex Mini SDI to HDMI or Teranex Mini SDI to Audio), you could probably feed that timecode to the MixPre's Aux input. Then set the MixPre record trigger to timecode run (rather than using the start/stop record flags).

Another possibility is to use the MixPre's USB port which supports USB keyboard commands for control of various actions (such as start/stop recording). So you could use a USB keyboard emulator to send commands to the MixPre from some other source. For example, recent versions of the Rasbperry Pi with a USB OTG port (like the Raspberry Pi 4 and Raspberry Pi Zero) can be configured in USB device mode (rather than the more typical host mode) and used to emulate a keyboard. There are various tutorials for this online: https://randomnerdtutorials.com/raspber ... board-hid/
https://mtlynch.io/key-mime-pi/

Or this project which is a slightly different approach, but along the same lines to create a network enabled USB keyboard emulator: https://github.com/Flowm/etherkey

Then you could maybe use one of the Generic network request modules in Bitfocus Companion to send a start/stop command to the Raspberry Pi over the network and have it send the equivalent keyboard command into the MixPre.

Thanks for all this, Dave. I'll share the USB info with the engineer who tried to get this to work for Companion; maybe it'll give them some clues.

As to the Teranex solution — that may work, however I'm running constant timecode, not start/stop timecode, in my studio. So that'd break that.

The USB solution really should be the way to do it. Thanks again.

Dave Del Vecchio wrote:Another possibility is to use the MixPre's USB port which supports USB keyboard commands for control of various actions (such as start/stop recording). So you could use a USB keyboard emulator to send commands to the MixPre from some other source. For example, recent versions of the Rasbperry Pi with a USB OTG port (like the Raspberry Pi 4 and Raspberry Pi Zero) can be configured in USB device mode (rather than the more typical host mode) and used to emulate a keyboard. There are various tutorials for this online: https://randomnerdtutorials.com/raspber ... board-hid/
https://mtlynch.io/key-mime-pi/.

I tried using an Arduino as a keyboard emulator to control my MixPre 6 and it refused to work. The keystrokes registered fine on every device I connected to except the MixPre. Sound Devices refused to discuss anything regarding their USB implementation, saying it was "engineering info". I ultimately pulled the controller out of a USB keyboard and had the Arduino trigger relays that simulated keypresses. Not ideal but it worked. Maybe the Pi will work better…