Converting Video to MP4 Can Shrink or Grow a File, Depending on Bitrate

A test of five video conversions by CompressVid, an online video toolkit, found that changing format to MP4 could cut file size by up to 77% or increase it by as much as 79%. The company explains that the container format itself adds very little to file size, so the real change comes from the codec and the bitrate chosen during re-encoding. When a tool transcodes to H.264 for compatibility, the new bitrate can be much lower or higher than the original's. Results also depend on the source, since phone recordings with high real-time bitrates may still produce larger files than an H.264 encode. The findings suggest that the file extension alone does not determine size, and that the encoding settings matter far more.