So I can get this straight, you've got a video made of I-frames and other (dependent) frames:
Code:
I???????I???????I???????I???????I
And you are able to cut out an I-to-I section which plays back fine:
We could say that's 56075-56195 (both I frames, if I read your post correctly).
But if you're cutting, don't you have to be sure that you are
only discarding non-I-frames? Your "subtract 2 in order to be safe" doesn't seem consistent with that.
You should - again, if I've got this right, I might be wrong - only try to delete 5607
6-5619
4. If you delete any I-frames I think you'll ruin the GOPs either side, won't you?