HDMI audio injection

Howdy porch pumpkins,

Question for the motion-video-knowledgable among the crowd. I’ve been shooting home-recorded talks during pandemicae (against my will), for which I’ve primarily opted to use my Canon 5d3 — with its HDMI-out straight to a high-quality HDMI hardware capture device. That goes into OBS Studio, so I can live-toggle between slides and the hero shot of myself hunched over the keyboard.

HOWEVER, as the EOS gang undoubtedly already knows, Canon in its infinite foresight saw fit not to give the 5D3 an audio-out signal on the HDMI monitor socket. Which you’d think would be fine; I have an external shotgun mic that’s better than the built-in anyway, so I run that separately to the recording PC as its own channel, and sync.

Except that about once out of every five times, the audio-in channel get crunched down by static. I’m assured that this is likely the fault of PulseAudio on the host system (or, at least, that’s what most people say. Linux system-developers, strangely enough, are certain it’s an application-level problem). Unregardless, I’d like to attempt to bypass the whole question and fix the problem before it occurs. So I went looking at how to inject audio into the HDMI connection.

Turns out there are a few fly-by-night / grey-box manufacturers out there who sell clunky steel boxes for audio-in-to-HDMI operation. But reviews are super mixed as to whether or not they actually work. So I wondered: does anybody have any experience with this sort of device, or with piggybacking an audio signal onto the 5D3 HDMI through some other means?

It’s a plain analog-stereo signal. But clearly some of the “injector box” devices won’t add audio to a signal that has no audio on the input side, and stuff like that.

I’ve pinged a couple of videography geniuses already, who all said they’d just record audio to a separate, more expensive dedicated device to begin with. But that doesn’t really solve my setup.

Any wisdom to share?

Time for Pipewire! You can split the HDMI off and composite the audio back in using pipewire and the very new wireplummer session manager. Welcome toooo there fuuuttuuurrrreeeee

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What do you mean “split the HDMI off”?

The problem isn’t that I have something I need to split, it’s that I have things I need to combine. Was something unclear about how I phrased all that?

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It was clear what you were looking for to me - unfortunately my only experiences have been going the other way.

But what you’re looking for is a common thing, I wouldn’t consider stuff carried by B&H to be fly-by-night, and they’ve got a whole category for it:

Some of those are for SDI and not HDMI, the SDI ones are MUCH more expensive. I think Monoprice has their own embedder?

I meant split the HDMI audio stream out (and get rid of it).

At any rate, pipewire should be able to handle this, its nodal!!

I meant split the HDMI audio stream out (and get rid of it).

At any rate, pipewire should be able to handle this, its nodal!!

Right. Well, that’s the opposite of what I asked, and it’s also the opposite of the hardware/software divide at the beginning, so … thanks for the enthusiasm, I guess, but I’ll be moving on.

Yeah, in general (emphasis on general) I haven’t had bad experiences with B&H; certainly not when compared to Amazon or other generic-reseller outlets. But that begins to break down when you get away from the brands that are already established on their own, and moreso when you’re dealing with the “oddball gadget” categories and not, say, lights and lenses.

For example, I don’t know either “Sescom” or “A-Neuvideo”, and both of their devices on that page appear to be repackaged versions of the same box:
as does “Vaddio”'s, with possibly some different I/O:

So I don’t have a lot of faith that any of those are well-supported and not bulk-manufactured-untested-DSP stuff that will die 50% of the time (as some of the reviews on, e.g., the Sescom one, say). Then some of the others will claim that they can insert audio into an HDMI signal that has none, but comments will say that it only replaces audio on an HDMI signal that already has a silent audio signal.

Which is why i was really hoping I could find someone who had done this in practice.

Yeah, sorry - unfortunately, I’ve only gone in the opposite direction - splitting an optical stream out from HDMI for compatibility with an old receiver that didn’t support HDMI audio.

At least one of those was only $100 or so, so it isn’t exactly a risky bet - especially since B&H has pretty good return policies. I think some of those embedders are also available on Amazon which has even better return policies.