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Black Magic Video Assist 7" 12G and Canon C300 MK III


I am trying to connect the above BM Video Assist via HDMI to my C300 Mk III, but no matter how I set either device's settings, the video assist keeps reporting, 'no signal'.  I have changed HDMI cables but still no success. I have used the same video assist with a Panasonic S1h and it works fine, and I am hoping that there isn't a problem with the C300's HDMI output port.  Is there a compatibility issue with the C300 and the video assist?

Thank you in advance.



Product Expert
Product Expert


I'm not very familiar with the Black Magic Video Assist series but the Black Magic site says the 12G HDR model supports up to 2160p 60p. According to the HDMI Video Output Configuration chart for the camera (Page 148 here: if you shoot RAW video at 2048x1080, any frame rate, with Progressive scan mode, the HDMI output resolution would be 3840x2160 so those settings should not present an issue for the monitor. It looks like the chart shows a few compatible options when recording in XF-AVC as well.


Thank you for your reply.

On paper, it appears that the Video Assist should work with the C300 Mk III, and Black Magic's promo material claims that it will work with any HDMI camera, however, if that's true there would not be a need for a 'list of compatible cameras'.   And I've noticed that while the Canon C200 and R5c are on the list, the C300 Mk III is conspicuously absent.  Fortunately, I did not purchase the Video Assist specifically for the MK III, as I had it on hand from a different application. That said, In an attempt to ascertain whether the problem is cable related, I replaced my HDMI cables with a brand new Monster ultra high speed HDMI cable, and it's still a no go.  I have an Atmos V+ arriving towards the end of this coming week, and if I find that I too does not work, then I will know that there is a problem with the camera's HDMI board and will send it in for service, as it is less than a year old.

Thanks again.


This is a followup to the prior Video Assist post.

It appears that the Black Magic Video Assist will work with an SDI signal sent from the C300 Mk III, but not over HDMI. I find that strange, but hopefully someone more knowledgable in the HDMI protocol can explain why it does not work.  Unless I had misunderstood Canon Cine Tech support, both the HDMI and SDI signals originate from the same board, so if one is working the other should as well, but my logic could be flawed. 

ADD:  I've just connected the MK III to a computer monitor via HDMI and it works fine.  That leaves two options: 1. either the HDMI port on the Video Assist is defective, or 2.  There is an incompatibility with the HDMI handshake between the two devices.

I am now 99% convinced that it is a compatibility issue, and here is the logic:
1. The Video Assist works with the C300 Mk III via SDI, but not HDMI.
2. The C300's HDMI output freely transmits signal to a computer monitor, so the output has been proven to be functional.
3. The Video Assist works via HDMI when connected—within the past 30 minutes—to a Panasonic S1h, proving that its HDMI port is working.
4. As per the above, I am left with the only reasonable conclusion, that being that there is a compatibility—handshake—issue with the Canon C300 Mk III/Video Assist 7" 12G combination.
If you, or others, have an alternative explanation, I would be eager to hear it.
Thank you for your assistance.


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