VideoMach can skip some frames from the input file, so when you execute the conversion they won't be present in the output file. Here's how to delete a segment in the middle of your video:

1. Move the preview slider to the first picture you wish to delete.
2. Click File > Split Here.
3. Move the preview slider to the last picture you wish to delete.
4. Click File > Split Here.
5. Mark the previous (middle) segment and press Del to delete it.