Why do some devices not play back my files, particularly AVIs?

Firstly AVIs were invented as a way to pay videos on PCs, and Apple developed MOVs so sticking AVIs on a mac is an after thought.  Also AVis can be made up of different types of audio and different types of audio and since it is windows and fairly open – unlike MACs which are pretty closed – lots of people made their own types of video and audio which you can only read if you install their codecs as they don’t come with Windows as standard.  They may not even have made MAC version of them.

Computers can at least have stuff installed to cope with stuff they don’t do natively but projectors cannot.  Thats why its best to keep to standard types of files like MP4.  Even then MP4s can be made of H.264 or H.265 video and the audio can be AAC, AC3 (dolby) or WAV.  The video can be 8 bit or 10 bit ( that refers to the colour – 10 bit is more info than 8 bit so better).  Lots of things can’t play 10 bit MP4s but can play 8 bit or can’t read MP4s with WAV audio, or have trouble playing H.265 cos its new and hard work.

H.264 vs H.265
H.264 is the standard way of doing MP4 files although there were other MP4 formats before this.  H.264 was the first time MP4s could be a reasonable quality.  It can go up to 4K and you can vary the bitrate (how much data the file uses per second).  Put the bit rate too low and it will look crap, too high and it may not play back off a USB stick which can only do a certain speed.  The right bit rate depends on how big the picture is – SD, HD or 4K, and what is going on in the picture – blue or green and fast moving is harder to do that simple scenes.

H.265 is basically the same thing but better so you can get a similar quality picture but in a smaller space.  Many cameras are now using this.  Because it is more compressed it harder to play back as well so you need a better computer or playback gizmo, and because it is new fewer things can play it back at all.