I can stream video (viewfinder output) from the IXUS160. Higher quality video is desired. Looking at these Canon models: G7x, G9x, SX60, and EOS M10.
Several important considerations:
The fact that a camera can record better quality video does not mean the chdkptp viewfinder output will be any better. The two are essentially unrelated.
All the cameras you mentioned Digic 6 cameras, and none are yet supported by CHDK. I'm working on the G7x, and some partial work as been done for SX60. I'm not aware of any work done on the others. Additionally, the display related framebuffers have changed significantly in Digic 6, so features that were standard on previous version of CHDK and chdkptp may not be immediately available. Currently a
special hack is needed for live view on digic 6. I will work on getting this into the main chdkptp code after I have G7x to a point where I can work on this.
Related to the above post, Ant apparently has made a CHDK port for the EOS M3, but the AFAIK code has not been published so I can't comment on how complete it is, nor whether it will ever be officially supported. Also note that the original EOS M uses Canon's DSLR codebase, and so will never be supported by CHDK (IIRC, there is a magic lantern port). The EOS M3 uses the P&S codebase. I haven't seen confirmation that the M10 is also on the P&S codebase, but considering it's a budget follow-on to the M3, it seems likely.
I thought I read somewhere CHDK & chdkptp can be used to switch the camera to video record mode and have access to the image sensor's video output stream (not the viewfinder.)
This isn't really correct. The live view protocol only accesses the buffers used for the camera LCD. You can switch to video mode (which affects the resolution of the LCD buffer on some cameras), but this does not give you full quality video the camera records.
chdkptp live view is generally quite low resolution, usually 240 or 480 lines depending on the camera. It also suffers some other problems, due to the way it's hacked into the Canon code: It isn't synchronized with the cameras frame rate, it just gets whatever the current frame is when the client requests it. This results in unsteady frame rate, skipped or duplicated frames, and tearing.
I thought I understood that it is possible to capture the video stream from the image sensor, not the viewfinder, IF the camera supports taking a still image while video recording is active. True?
This is not correct. I think you are mixing up CHDK PTP live view with the cameras standard (analog or HDMI) TV video out. On many recent cameras (especially low end ones), you can only use the video out in playback mode. On others, you can use it while shooting. On most (all?) you can only use the SD out while shooting, not the HDMI out. According the the G7x manual, it supports SD video out while shooting. This is described in the "Playback on a standard definition TV" section.
On a camera that supports video out while shooting, you can theoretically use an external video capture device connected to capture the video stream, it may be better in some ways than the chdkptp live view. However, on most recent cameras, the SD video out uses the same physical connector as the USB, so to use CHDKPTP at the same time, you must construct a
splitter cable.
This is all unrelated to shooting stills while
recording video.
