...The "video quality" option adjusts the compression level...
could you please be more specific about this option?
thank you
The G1X (like other Canon cameras that record H.264 video) attempts to maintain a constant quality in the video rather than a constant bitrate. The bitrate (and file size) will depend on the content being recorded - using the default camera settings I've seen 1920 video recorded as low as 50MB / minute up to 250MB / minute.
CHDK allows you to override the 'quality' factor applied. The values you can enter range from 1 - 99, where 1 is the lowest quality and 99 the highest. The default camera setting is approximately equal to 84 in the CHDK override.
A setting of 99 will roughly double the average file size, a setting of 1 will be around 1/2 - 1/5th the average file size; but the actual size can vary greatly as I said depending on content.
A high speed class 10 card should be able to keep up even at quality level 99 - I use a Lexar 400x card with no problem.
The last issue is the 4GB file limit - at quality 99 you can easily reach the 4GB limit in around 8 minutes recording 1920 video.
Phil.