Most compression tools have the ability to set I/O points

When you're testing and tweaking your compression tool of choice, you'll probably should test what you're doing rather than just running the settings on your entire file.

Did you know that most compression tools permit the setting of In/Out points (as a test for your video?​)

Compression Tips like this can be found by attending sessions at Post Production World at NAB (this link includes links to non-PPW sessions)