How target size works
A file's size is its length multiplied by its bitrate. The tool divides your target by the length of the video, takes off what the sound needs, and encodes the picture twice: the first pass measures which moments are hard to compress, the second spends the bits there. The result lands under your number. If the budget is too small to look acceptable at the original frame size, it steps down to 720p, 480p or 360p instead of filling the picture with blocks.