We have thought about this, but don't yet have public solution. GPMF timing does extract information from the MP4 wrapper today, whereas livestreaming isn't using MP4. Other then a small amount of precision loss in timing, for where would you hope to extract metadata? What data stream?

I would like to extract data from the sensors integrated at the GoPro (integrated IMU: gyroscope, accelerometer...) just to avoid using an external component.

My idea is to record from a GoPro camera and stream video, sensor data to a control hardware (some espressif chip) for my FPV project.

Where would the data be extract from, technically? This is the issue this need to be determined.

From the telemetry that came with the MP4 (GoPro video metadata)

Sorry if maybe I didn't understand at all the question.

The problem is when streaming data, there is no MP4, so where to want to extract the telemetry from? There are no standards for this, something new is needed.

Do you know if there is another way?

I want to know where a developer using livestreaming would like to see the metadata stored, on a technical level. Otherwise this is too much hand waving.

And what about an non technical approach? Just to show a bunch of people how fast the pilot is going at a race, just for streaming purpose

It has to be implemented using technology. That is the problem. We have the data, just need to know which pipe to place it. Remember it will be up to a third party to extract it, so where would a third party expect to extract it? Livestreaming has a sender (GoPro can do) and a receiver (everyone else.) So the issue is on the receivers not having a standard place to store metadata.

In your original question: It is possible to use the metadata to feed a control system?
Sure, what control system, and where is it expecting to read telemetry data?

It's looking like this ticket came from someone without a full grasp of the technical complexities at play here. As someone with a somewhat knowledgeable grasp of the issues at play (not nearly as knowledgeable as you or Daryl), I would posit that if this request is going to be taken seriously, the best solution would be to stream the data over IP/MQTT. The GPMF standard is open source, it's up to developers of relevant software to add real-time streaming support. My understanding is this functionality already exists for STANAG 4609, which is another (standardized) KLV format akin to GPMF.

https://standards.globalspec.com/std/1222789/stanag-4609
https://www.impleotv.com/content/klvstreamer/help/page_klv_in_t_s.html
https://github.com/impleotv/gstreamer-test-klv
https://www.vitec.com/fileadmin/downloads/Collateral/VITEC_MilitarySolutions__Brochure__22-E.pdf