I thought from my one long test that the max file size was 3.665Gb -
However I also ran a Zx3 test at Wvga -
Zx3 used a similar strategy of filling up to a max file size then used a "continuation" file -
the max file size was different from that at 720p/30fps.
Zx3 Wvga (854x480)
The max file size at wvga = 2.718Gb
for ~1h 16m = ~0.6 Mb/s
"continuation" file wvga -
1.018Gb (filling up the remainder of the 4Gb SDHC card) for ~ 28.5m = ~0.6 Mb/s
(note my Zx3 battery still had capacity after the 4Gb card ran out of space -
that's after ~1h 44m)
This is not absolutely conclusive,
and I have not done the equivalent long tests on 1080p or 720p/60fps -
but it seems that the Zx3 fills up to a certain max file size
which may be dependent on the video resolution used
(since the max file sizes for 720p/30fps is different from the wvga)
- then will use a "continuation" file -
I do not know the max limits of the "continuation" file -
but it seems a sensible guess that it will be similar to the respective first max'ed out file sizes.
I now have an 8Gb SDHC - and did some more Zx3 battery endurance tests -
I used 720p/30fps because that is what I normally shoot at.
Time I managed was 1h 48m compared to my Zi8's 1h 38m -
but those were two different samples of the Kodak KLIC-7004 battery supplied with the camcorders.
So I used the battery from the Zi8 in the Zx3 from full charge to shutdown that sample lasted 1h 44m - so now we can compare Zx3 managed about 6 mins more on the same battery as the Zi8 or just over 6% more time.
In the course of these battery runtime tests I also got a number of maximum sized first files - and they were 3.666 and 3.667Gb with time length 1:04:34 to 1:04:36.
So from this the Zx3 is about 10% better in using its battery over the Zi8 - but takes up almost 3x the storage for the same video.
At 720p/30fps Zi8 I can get about 3 hours on a single 4Gb -
whereas on the Zx3 1h 06m on the same 4Gb
an 8Gb card will only hold 2h 12m.