Q:

Mixing audio with HDMI video to replace the sound from the camera

I would like to live-stream from a camera, but replace the audio from the camera with a higher-quality mixed soundtrack, ready for sending over HDMI to a transmission device.
How can I do this?
I know that the Tascam DR-701D has two HDMI ports (in and out). Could I use this as the mixer to replace the soundtrack on the HDMI video feed, ready for transmission, or is there a better way?
Details
The video will come from the micro-HDMI port on the camera.
The audio will come from one of three sources:

XLR stream from the event
Directional XLR mic
MP3 player

The audio will be mixed together by a mixer during the event as appropriate.
I now need to mix the audio from the sound mixer with the video from the camera’s HMDI port (which will have an unusable poor-quality audio track from the camera). How can I do this?

A:

It seems that what you are looking for is an HDMI audio embedder.
It seems that the Tascam DR-701D offers this functionality as described in Outputting this unit's audio as the HDMI output audio
Examples of external alternative such products can be found here (I am not affiliated with these manufacturers, other products might exist):
Kramer FC-69
Extron HAI 100 4K

