[RFC] Using UVC as a monitor

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I'm pulling together code at the moment which I'll post for comment later in the week.

What I want to do is combine the operations of 2 drivers to create a virtual monitor via UVC, uvcfbsource

It involves configuring the UVC video-streaming capability of the USB Webcam Gadget to use a framebuffer as it's source.

The SimpleFB driver currently in the kernel requires the framebuffer memory to be allocated by some other program/driver - so it seems a good choice for the framebuffer.

Using the current capabilities of the USB webcam gadget, it seems for a simple solution all I need to do is have a userspace application which grabs the framebuffer data, wraps it into a videobuf2 format and inserts it into the queue.

In this mode, the "Monitor" becomes any application capable of displaying streaming video - for that matter, if multiple instances of the userspace application are executed then you can have multiple monitors all displayed on the same computer.

Purpose: I am working with a couple of ARM development boards, primarily the BeagleBoneBlack. Using a usb montor gadget, I can give my BBB a monitor without actually having to plug in a monitor.

In simple mode, the framebuffer would be configured with a resolution of 720p and to store data in the YUV format so it matches one of the currently defined formats in the Webcam gadget.

Beyond that though, I'd like to extend this to a smarter kernel driver which could: 1) Use the start streaming/stop streaming USB events to emulate hotplugging the monitor. 2) Allow for different resolutions to be supported and controlled by the remote computer[IE show different options, and allow the webcam viewer application to choose one of the streams]
3) Allow for the complete set of UVC supported YUV formats for frames
4) Switch from the video stream UVC encapsulation to the frame buffer stream

Using UVC in this manner has the downside that full uncompressed frame data is being transmitted over USB - however UVC does provide a number of optional compression and encoding methods - so it's possible to improve performance if there is demand for it. It is also possible to use 'vendor defined' compression and encoding methods if those are not sufficient. Since UVC allows the gadget to advertise multiple capabilities - a device using the uvcfbsource driver could be used by any system supporting standard Webcams - Mac, Windows, Android, Linux, etc via the uncompressed format - while the compressed format can be used if the viewer application supports it.

I wanted to check now to see if there is something I'm missing, or known projects already working on this sort of thing, before I start coding.

My long term goal is to use the code developed for a fully functional uvcfbsink driver to create a uvcfbsource driver: ie an application which reverses the process and receives data from a uvc "webcam" and pushes it into a framebuffer. That would allow for creating an open source alternative to DisplayLink while avoiding any usage of their API and any potential patent issues.


-Gary






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