Hitting a Video File-Size Target Comes Down to Bitrate Division, Test Runs Show

A video's file size is largely determined by its bitrate, so a target size can be converted into a bitrate budget by dividing the target bits by the clip's duration. The author, who works on the online compressor CompressVid, shares a formula that accounts for audio bitrate and container overhead, and notes that a size limit is effectively a bits-per-second limit. Test runs with the tool showed that the same target produced very different results depending on the source footage. The author attributes this to encoders spending bits only where needed, since phone footage tends to be over-encoded and complex or fast-moving scenes need more bits. The figures come from the company's own tests, and the author flags which numbers are tool-reported versus his own calculations.