Avidemux HD settings help needed

[vorton]

I am using Avidemux to hardcode subtitles onto my 5GB .m2t format HD (1280x720) files.
My video is 45 minutes long.

Goal: to have a resulting video that is below 1GB and no frame drops.

After trial and error testing for a few days, i have found these settings.
They produce a relatively small size file (500mb) with excellent quality.

Video format: MPEG4 AVC
Encoding mode: Constant rate factor (Quality 23, "max.constant rate factor" ticked, Quantizer set to 0 (High Quality).
Audio: MP3 (lame, 256kbps)
Format: AVI (default settings)

The problem: Still in areas like "end credits" there are noticeable frame drops.
I have tried all the other encoding modes (Average bitrate, Target size 700mb, but do not work as well for me as Constant rate factor mode).

What can i do? Am i missing some settings?
Do i need to set other settings, like keyframes?

[vorton]

Quick update: I got rid of the frame drops by setting format to MP4!!

Excellent, this is just plain old fashioned excellent!