Jan Grulich

PipeWire Camera Support in Firefox #2

I wrote the first blog post about PipeWire cameras in Firefox in May and a lot has happened since then. The first PipeWire support arrived shortly after the blog post was published and was released as part of Firefox 116 (August). We didn’t enable it by default, of course since it’s still a “work in progress”, but many of you tried it (thank you for that) and we were able to fix some issues that I, as the only tester at the time, hadn’t found. However, aside from all the crashes and minor issues we were able to fix relatively quickly, there was one major problem (or drawback) with the PipeWire camera that made it unusable with most popular video conferencing sites, such as Google Meet. Kind of a deal breaker, right? This has kept me busy ever since, but we are finally close to fixing it in upstream. I’m going to explain why this was a problem and how we fixed it, and forgive me in advance if I write anything wrong, I’m still learning and discovering things as they unfold.

There are Javascript APIs that are implemented by all the major browsers. The API documentation is here. It defines APIs sites can use to query information about media devices. I will now describe a simplified workflow used with V4L2 on the aforementioned Google Meet once you start a meeting:

  • GMeet makes enumerateDevices() call to get information about available devices
  • Firefox can respond with the list of available cameras (+ audio devices obviously) on the system because the information about cameras is available and no permission is needed
  • GMeet makes getUserMedia() call to get access to the camera since it knows there is a camera available
  • Firefox will prompt the user to get access to the selected devices (including camera) and start streaming

Now the same situation, but with PipeWire:

  • GMeet makes enumerateDevices() call to get information about available devices
  • Firefox cannot respond with the list of available cameras because this enumeration request cannot ask for user permission and we cannot access PipeWire without it. Firefox will return an empty list of camera devices and there will be only audio devices announced
  • GMeet makes getUserMedia() call, but only to get access to the devices that were previously announced, so only audio devices
  • Firefox will prompt the user to get access only to the selected audio devices and no camera

How did we solve this?

The documentation here also covers this situation. The enumerateDevices() request is allowed to return a placeholder device for each type. This means that we can return a placeholder camera device, which tells Google Meet there is actually a camera device to ask for. With this device placeholder, the subsequent getUserMedia() request will also request access to camera devices. How do we know that a camera device is present without having access to PipeWire, you ask? The camera portal from xdg-desktop-portal has a IsCameraPresent property for exactly the same purpose and we use it to know whether to insert the camera device placeholder or not.

While such a solution sounds simple on paper, it required a significant amount of changes to the entire media handling stack. There is not a small amount of PipeWire specific code, so this fix also involves some restructuring so that all the backend specific logic is in one place. And while I’m getting more and more familiar with the Firefox code, which is helping me to progress faster, there’s still a lot to learn.

Anyway, the reason I’m writing this blog post now is that all the related changes have been approved and will hopefully be landing soon, making Firefox fully usable with PipeWire . Although not yet merged, Fedora users can use a COPR repository I created. The repository has Fedora Firefox builds with all the necessary changes backported and PipeWire camera enabled by default. Just note that while I’ve been testing and using it for the past few months and it’s worked perfectly for me, you use it at your own risk. You better to use it just to test PipeWire camera support as the official Fedora Firefox package is the one we keep fully updated and my repo may lag behind. There will be a new PipeWire 1.0 release soon, which will be a big milestone for PipeWire and I hope that PipeWire camera support in Firefox and browsers in general will be part of the PipeWire success story.

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