: Lowering the bitrate is the most effective way to shrink an MP4 without changing the resolution.
: The ".31" in the name typically indicates this is the 31st part of a larger series, likely a course or curriculum. So Big.31.mp4
: As an MP4 , the file uses lossy compression (often H.264 or H.265) to balance high video quality with a manageable file size. : Lowering the bitrate is the most effective