Cellphones have excellent sideloading options. USB and Bluetooth file transfer may both be supported and if the phone has removable memory cards it is possible to write to them and insert them into the phone.

Bluetooth

The built-in support for Bluetooth in newer Macs is excellent for transferring video into cellphones. If you have this option you can be viewing videos on your cellphone within minutes.

USB

While Macs have advantages for Bluetooth file transfer, when it comes to USB the situation is reversed. This is largely because the proprietary drivers used by most phones are Windows-only. Unless the phone mounts as a mass storage drive it is unlikely to be accessible from a Mac.

If you are fortunate enough to have a phone like the LG KG800 (Chocolate) you can use the Finder to move files into the phone.

Memory Cards

Removable memory cards come in a variety of formats and sizes and are not supported on all cellphones. However if your phone supports removable memory cards and you have a card reader, then this is a great sideload option

Memory cards have huge capacity for video storage and data transfer speeds are very high.