Dropping Frames when Sequence is set to RT-unlimited

either your low on memory or your sequence settings are incorrect.

 

Ducks in a row

Your HFS10 is AVCHD. Using Log and Capture in FCE will seee that footage imported as Apple Intermediate Codec.

MOD files are, I think, MPEG-2 files. FCE will want them as something else before it can work on them. I use MPEG Streamclip for my conversion work when I need it - but you do have to have the MPEG2 playback component from Apple to playback MPEG2 streams

The iMac is able to playback all the video you give it but adding effects transforms the video. Your Mac then has to calculate the effect of each effect as it plays back in real time.

Real Time effects playback will work for (a) some effects and (b) up to a point. Then you have to render. The joy of video.

You will get best results out of setting up your sequence to match your video in the beginning, then importing/capturing/dragging 'n' dropping your video, then applying effects. Also, choose the FxPlug effects when given a choice.
http://www.apple.com/finalcutexpress/#compositing

 

If it's bothering you, then turn it off from the popup window or from the User Preferences window. It won't play as smoothly but enough to give you the idea, and it won't affect your exports.

 

Put it to Safe RT, also change the Quality of playback to "Dynamic". Then once your done editing do a full render and then put everything back for full quality mode for screening. This way you can keep editing without errors. Also make sure your hard drive is fast enough and not over 80% full as this can affect performance.

 

AVCHD in FCE become AIC... which has a high bitrate. You have your footage on your iMac's internal drive. This is your problem. Store all video for editing on an external firewire hard drive and you'll be fine.

 

Is this due to an issue with internal throughput? I'd understand and recommend it on a laptop but an iMac has a 3.5" 7200rpm drive.

Can you let me know? Very interested to hear as I'm looking at an iMac for some "heavier" video work.

 

it's just the fact video requires long sequential reads which get interrupted when the media is on the OS drive.

always ALWAYS keep the media on a drive separate from the OS. this goes for any format and any computer