Since the last time I used a Kingston class 4 card for my test, I did the same test again using a Transcend class 6 card. The result I got proved the above theory since the gap was only 5 seconds compared to 10 seconds the last time. Out of curiosity, I repeated the test again using the class 4 card and the results surprised me.
No, it is not because the gap was shorter than using the class 6 card but because it was shorter than what I measured the last time. This time it was only 7 seconds compared to 10 seconds previously! Not sure if this was the SDHC card itself that affected the results, I repeated the test again with my 2 other Kingston class 4 cards. The results were very similar, one also gave 7 seconds and the other, 8 seconds. For some unknown reasons, the gap is somehow shorter than when I tested it the last occasion. I can only suspect that the cards are now more seasoned after being in used many times and the read/write is a bit faster. Who knows?
To confirm the results, I tested using the Transcend class 6 card again. The result was, thank goodness, consistent at a 5 seconds gap.
For those of you wondering, this is how I did the test; nothing elaborate but something very simple and which I think is fairly accurate. I left the camcorder to run on recording and when the end of file countdown come on, I video the Windows clock. Thus it will show the time the recording stop and also the time when the next video starts again. The difference in the two times captured on video will be the gap. There is a possible error of +- one second but good enough for this purpose.
BTW, there are also slight differences for the length of the video of the 4GB video among the cards used and it ranges from 23:39 to 23:48 using just the length of the video shown on the video playback listing screen.
To sum it up, these are my findings. You'll be the judge to say whether it is conclusive or not.
1. There is a gap between the end of the first 4GB file and the start of the next 4GB file.
2. Using the higher class 6 SDHC card will reduce this gap as compared to a class 4 card which is about 5 seconds as compared to about 7 seconds from the test carried out
3. The length of the video at 4GB also varies slightly depending on the card in use and ranges from about 23 minutes 39 seconds to about 23 minutes 48 seconds.
4. Use a class 6 SDHC card as far as possible.
If you are recording a long video that may exceed the 4GB limit and knowing the above figures, it is best to stop the recording manually at a suitable time before it stops automatically in order not to miss out any critical moments that you wish to capture, should they occur during the gap.
I believe this gap will also occur in all camcorders that uses the FAT32 file system but it may vary for the different brands.