As long as the file size is converted in the same format as the source file, the video resolution is the same as the source file, the quality remains unchanged, and the file size will not increase. But in this case, conversion and no conversion are the same, and the reason that will cause your problem is generally because the file, resolution and coding method (mainly code stream) you generated are larger than your source file, so the file you generated is much larger than the source file.

No matter what format, it mainly depends on the code stream and resolution. When both come down, the files will be slimmed down, but the quality will also decline.

At present, the coding formats of RMVB and H264 have the highest compression ratio.