Are you trying to convert a video so that it can be played on a mobile device? Compared to other devices there are certain factors that you will want to weigh more heavily for them, and may affect your decision on the format that you want to use.
In particular the three factors that are the most important are:
Optimized for a Single Device or General Use
The first thing you need to consider is whether you’re converting the video to watch on a single mobile device, or mobile devices in general.
If you are converting the video for a specific mobile device you can optimize it accordingly. However because of the fragmented nature of mobile devices, that may mean that you could have difficulty viewing the video on other devices.
In most cases the safer approach is to optimize broadly for the majority of mobile devices unless you have no intention of watching the video elsewhere.
Compatibility and Hardware Support
As you probably know compatibility is a factor that is always important when considering video formats. However on mobile devices that is doubly the case, and you will want to ensure your video format is not just compatible – but can be decoded using hardware.
Rely on software decoders to play video formats on mobile devices is far from ideal. The power requirement for software decoders is higher, and it will weigh heavily on the battery of your device.
As such it is best to only use formats with hardware support – and MP4 with H.264 is a safe option in that regard.
Storage Space and Compression
Another limitation of mobile devices is the storage space that is available. Nowadays it tends to vary between 16GB and 128GB or around that region.
That storage space can get filled up very quickly if you transfer multiple videos over to your mobile device – which is you will want to take it into account and consider the compression that is used. If supported it may be worth converting videos to formats that have better compression and can reduce their file size.
The only caveat is that many of the newer formats with better compression than MP4 with H.264 are not supported on all mobile devices. In the last few years HEVC has started to gain more support though, so it may be feasible.
In general MP4 with H.264 is the ‘best’ format for mobile devices right now as it offers decent compression while being compatible with most mobile devices. For example if you learn how to convert MOV to MP4, the file size will be significantly smaller.
However if support for HEVC continues to grow or if other formats such as AV1 become as widely supported, it may soon be better to use them. At the end of the day that is why you should consider each of the factors listed above independently to determine which format you want to convert your videos to.