And the short answer is… NO.
I installed the CHDK firmware on my Canon SX200 IS (1.00c) tonight, and made some video tests. I shot high-detailed objects with the normal firmware (default video quality is 75%), and with the CHDK firmware at video quality “99%” (and with all its video quality-related options set to ON).
The result was that the 99% quality setting would produce over 50 mbps bitrate videos (instead of the default 24 mbps). This is good. Problem is, after inspecting the footage, there was only about 2% visual quality gain. I tried with a small moving object too, same result. You can view the test images below yourselves (saved as full quality, with decoder at full quality too).
The other problem was that with any quality over 85%, the SD card (or was it the DSP/CPU of the camera?!?) could not keep up. Sometimes the video would bail out after 1 second of recording, sometimes after 6-7 seconds. Only below 85% it was stable with a Class 6 SDHC card. And this made that 2% of gain, disappear too.
Here’s an actual JPEG image, captured in AUTO mode, and then resized to 720p and re-saved again with only 75% quality. Even after such harsh treatment, that image is zillions of times better than any still from the videos I captured.
If the CHDK developers did not actually have any bug in their video tweaks, it means that the Canon digicam videos lose tons of quality DURING capture/resizing, internally, before the footage even reaches the encoder! So that would be a weak DSP they use, rather than a weak encoder.
Finally, the histogram, and zebras did NOT work on video mode with the CHDK firmware! Obviously, the video mode gets very little love from the CHDK developers. Which is sad. I mean, one other big feature that filmmakers would love is additional 24p/25p support. But this feature is not even on their todo list!
So, unless you’re interested in CHDK for its photography features, don’t touch it for video. It offers nothing of note to us videographers.
UPDATE: I shot one more test, under better lighting conditions this time, during daytime. As you can see, the quality gain was still minuscule.