Make video smaller - which settings matter?

Another extension doesn't automatically reduce a video. Understand the difference between container, codec and bitrate and test a short fragment first.

An MP4 file doesn't tell the whole story

MP4 and MKV are containers: packaging containing video, audio and sometimes subtitles. The codec determines how a trace is encrypted. Two MP4 files can therefore have very different properties. With Media Info you can see which codecs, resolution and other attributes have a file before changing anything.

If you just want to delete an unnecessary audio track or add subtitles, you may not have to recode the video. MKVToolNix is intended for such container and track operations. For actual compressing you use for example HandBrake or Shutter Encoder.

Start with the device you're going to look at

A modern codec can be more efficient, but the receiver has to support it. Check your television, phone or assembly program. A little video that doesn't play won't solve your problem. Note also audio: a supported video codec does not mean that every audio codec works in the same container.

Choose a preset that fits your target and then change as little as possible. Keeping a high resolution may be necessary for a large screen, while a short instruction video in a small web view needs less pixels. In the case of screenshots, pay extra attention to text readability.

Constant quality and bitrate send something else

In a quality-oriented setting, the required bitrate varies with the content. A quiet scene requires less data than complex movement. The final file size is therefore not fixed in advance. With an average bitrate you send stronger on the amount of data and therefore the expected size, but the visible quality may vary per scene.

Moreover, a quality number is not directly comparable between any codec or encoder. Do not take a random number from a manual without checking which settings it uses. Hardware and software encoders can also offer other choices and results.

Make a trial with tricky images

Keep the original separately.
Choose a short fragment with movement, details and speech.
Export with a suitable preset.
Play the result on the real target device.
Check image, subtitles, sound and synchronization.

A still screen is not a good test for an entire sports video. Choose the hardest kind of image from your recording. Compare the processing time: a slower setting can be useful for one archive file, but clumsy in a large daily series.

Avoid repeated loss-making conversion

Always make new partial copies from your best source. Converting a already strongly compressed video to a higher bitrate does not retrieve lost details. Leave the framerate and aspect ratio intact unless you consciously need another output. If the trial is good, you can process the full video and check the result before you clean something up.