为什么使用 FFMPEG 为视频添加水印后视频大小会增加？

Question

I am adding watermark to video using FFMPEG where i use -preset ultrafast in FFMPEG command.which add watermark to video very fast but due to this my output video size increased.

ffmpeg -i input.mp4 -i mt.png -filter_complex "overlay=(main_w-overlay_w)/2:(main_h-overlay_h)/2" -codec:a copy -preset ultrafast output.mp4

Without Using -preset ultrafast

input video size 5MB and output video size 5MB

Using -preset ultrafast

input video size 5MB and output video size 11MB

Answer 1

As FFMPEG documentation says:

A preset is a collection of options that will provide a certain encoding speed to compression ratio. A slower preset will provide better compression (compression is quality per filesize). This means that, for example, if you target a certain file size or constant bit rate, you will achieve better quality with a slower preset. Similarly, for constant quality encoding, you will simply save bitrate by choosing a slower preset.

In other words there is a trade off between encoding speed and space optimization/compression. Try going for other preset like veryfast or superfast