Why is it that when I put a film onto my micro SD card it refuses to play on either my tablet or phone? The film format (MP4) must be OK because if I load it to the internal memory on either device it plays OK, both devices recognize the content of the card but refuse to play it. Many thanks.
You're probably using a card with a poor sequential read speed, meaning that your devices can't access the data fast enough. Check the speed rating on the card. For video use, it should either have a UHS speed (shown inside a U-shaped symbol) of 1 or 3 or a standard speed (shown inside a C-shaped symbol) of 10. If it's got a lower standard speed that could well be the cause of your problem.