Difference between revisions of "SoC"

Revision as of 16:47, 1 March 2007

Design Ideas

FPGA Theora Encoder for Videoconferencing

In 2005 Elphel implemented a subset of Theora video encoder in Xilinx® FPGA that is part of Elphel model 333 camera capable of compressing 1280x1024@30fps ([1], [2]), but the CPU in the camera was not fast enough for the job even when the hard part was made by the hardware. In the model 333 camera software was responsible for generating frame headers and Ogg encapsulation of the Theora bitstream provided by FPGA. Knowing that Axis Communications AB were going to release a new faster processor we decided to wait for it before proceeding with Theora in the camera and used plain old Motion JPEG for a while.

Now we have the the new Model 353 camera tested and released to production - the camera that has a brand new ETRAX FS, more memory and larger FPGA and is already tested in JPEG mode. So now it is a perfect time to resurrect Theora code in the camera and move forward.

Current FPGA implementation supports only INTRA and INTER NOMV frames - the goal was to provide efficient compression for the scenes where the camera does not move (CCTV, videoconferencing) and large part of the frame stays the same. To reduce the bandwidth more we need to utilize selective block encoding so if camera is looking at an empty hallway there would be no bitstream at all but INTRA frames - just header telling that no block was encoded.

Such ability to selectively encode blocks is already in the FPGA code but we never used it with the slow CPU - encoded block map is a part of the frame header and the header is built by software, currently - before the video starts. To move farther we need either add FPGA code to generate frame headers or make use of the faster processor and do it in software.

Such project requires both FPGA code development (we use, and the rest of the code is written in Verilog HDL) and driver/application code (usually in C). When I was writing code (and debugging it) for the original encoder of the 333 camera I had to do both, but it would be nice to make such development in a team.

AJAX Camera Interface with PHP/fastCGI

In March of the 2006 I published an article in LinuxDevices - "AJAX, LAMP, and liveDVD for a Linux-based camera". It was a result of an interesting project to create a camera web interface with sliders, semi-transparent overlays and other fancy features. It would be nice if you could create something like that with regular web development tools, but it that case I have to cheat - modify (and create new) CGI programs (mostly compiled programs in C, some - shell scripts) running in the camera provideing the server part of AJAX.

In the Model 353 camera there is more memory (64MB system, 64 MB video buffer and 128MB flash) and the CPU is three times faster. This allows to expand the usage of the mainstream web development tools in the camera - replace binary CGI programs running on the server (in the camera) with the PHP code - it seem to run nicely in the fastCGI mode in the camera with lightTPD web server.

LAMP-based DVR

Electronic Rolling Shutter Distortion Compensation