H.264, also called AVC, was standardised in 2003 and is still the codec most video on the internet uses. Its open-source encoder, x264, is what most compression tools run under the hood, including the encoder behind the measurements on this site.
Its case is not efficiency. H.265 produces noticeably smaller files at the same quality and AV1 smaller still. H.264's case is that it decodes in hardware on essentially every phone, laptop, browser, TV and set-top box shipped in the last fifteen years. Nothing else is close.
That makes it the right default in one specific and very common situation: when you do not control the device your file will be opened on. Sending a clip to a client, attaching it to an email, uploading it to a platform that will re-encode anyway — in all of these the risk of an unplayable file outweighs the 20-30% you would save.
Practical notes:
- Profile and level matter for old devices. High profile is standard now; a device from 2010 may want Main or Baseline.
- 10-bit H.264 exists and is a compatibility trap. Most hardware decoders handle 8-bit only.
- The preset is free quality. Slower presets produce smaller files at the same CRF for no quality cost beyond your patience.
If your video will be viewed by people you cannot ask about their hardware, H.264 is very hard to regret.