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I mostly use my Pentax to record myself playing guitar covers, when I'm not travelling etc. Anyway the problem is first noticable after this procedure:

1) I add the song I'm going to cover to the arrangement in the software I'm using to edit movies. I'll later on add me playing guitar over the song, thus having the original song in the background.

2) I also transfer the song to my mp3-player, so that I can hear the song as I play.

3) I take my Pentax Optio M30, "mp3-player A" (where the playback is) and "mp3-player B" (which I use to record audio at the same time as I record the video using the camera) with me to the place where I record my covers (I live in an apartment but I have a house as well, where I can play drums and stuff).

4) Now, I just press "record" on my camera and mp3-player B at the same time, and push a headphone leading from "mp3-player A" where I have the original song.

5) I return home, where my computer is, and put it all together in the movie editing software. In the arrangement, I have:

a) the original song
b) the video recorded using the camera
c) the audio recorded using "mp3-player B"

I put the video so that it's synchronized with the original song in the beginning. Then, I delete the audio in the video-file and replace the audio with the audio recorded using "mp3-player B", and synchronize it with the video in the beginning.

6) Now, everthing is synchronized perfectly in the beginning. BUT here's the problem: after a minute the video becomes less and less synchronized. After five-minutes it's REALLY messed up. However, the audio from "mp3-player B" and the original song ARE SYNCHRONIZED THROUGHOUT. This means the problem is the camera. It records at another tempo than reality.


To really test this, I've done the following "experiments":

I recorded me clapping my hands occasionally, with "mp3-player B" recording the audio and a camera recording the video, just like before.

1) My mom has a Pentax Optio M30 herself, so I tried using her camera first. Then I did just like before - I put the video recorded using my mom's M30 and the audio recorded using "mp3-player B" in an arrangement in the video editing software. I synchronized them in the beginning, so that the first clap I made sounds at the exact same time in both the camera-audio and the "mp3-player B"-audio. But after a few minutes they are COMPLETELY UNSYNCHED!

2) I did the exact same thing as 1), with the exception that I used my sister's camera, a Sony. But the result is that the "mp3-player B"-audio and the my sister's camera-audio remains synched throughout the entire arrangement!


CONCLUSION:
So I've definitely isolated the problem now, and I've even tried this in multiple video editing softwares. I'm now sure that Pentax Optio M30, whether new or old (me and my mom's cameras can't both be in need of repair), records video in a different tempo than reality. I haven't tried this on different computers though.

What can you do to help? If you also have an m30, try doing the same thing as me; record a video using the camera (about 5 mins long) clapping your hands once in the beginning and once after a few minutes, at the same time, record using an mp3-player, microphone, or any other device (maybe another camera?). Then, put the two files together in a movie editing software, synchronizing them in the beginning. Click "play" and you should hear that after a few minutes, your clapping will not be synchronized any more.


This was a very long post, so I hope you have time to read it. It's an odd problem, but that's because recording music-covers perhaps isn't the most common use. I'm very grateful for anyone attempting the above "experiment", or if someone knows what might be wrong. Thank you very much!