A simple, cheap and reliable media player that just works. No configuration needed.
Here are instructions to program your Raspberry Pi loop a video file endlessly and seamlessly, without showing any logo or breaks.
The video needs to be in the root folder of a connected USB stick (i.e. directly on it). If you have more than one video it'll play them in alphabetical order, and then loop around.
It uses both the 3,5mm jack and HDMI by default for sound output. Note that the quality of the sound output on the analogue 3,5mm jack is not as high-end as with some other media players. Use the HDMI sound output if you can. Or add some audio hardware like this digital-analogue converter (DAC) for high quality audio.
You can even hot-swap USB sticks. Remove a stick and insert a new one and it'll automatically start to play it.
A tip: The Raspberry is a full, working computer, and as such would prefer to be shut down properly. It seems to be OK however with simply being unplugged from power, but probably won't tolerate it forever, as the SD card can corrupt. If you can, just leave it running. It's built to run forever (and as a bonus uses very little energy).
Download the image file here:
https://www.khm.de/~sievers/net/Ada_Videolooper_v2.zip (Version 2 / June 2018, runs on all Raspberry boards, including the 2018 Raspberry Pi 3 Model B+). There's also still the older version 1.1 for all boards up to but not including the 3 B+.
Raspberry Pi boards are small in size, but they're full computers. The SD card serves as the main hard disk and holds the operating system. You'll need to clone the downloaded image file with the operating system plus the looper script to the card. See How to clone a Raspberry Pi image to an SD card.
Clone the image to the card, plug it all together, and then start it up by plugging the power adapter into the mains socket. That's literally it.
Here are the original instructions on how to set up the VideoLooper yourself, i.e. for the learning experience, or if you don't trust a downloaded image file. Many thanks to Adafruit.
Check out the detailed instructions by Adafruit, if you need to change anything, i.e. play the video directly from the SD card (i.e. when the video file is >4GB), or when you need to reposition the image (necessary on some analogue monitors).
Some useful commands:
ssh firstname.lastname@example.org to ssh into it when connected via Ethernet with a Mac.
ssh pi@raspberrypi if you're on Windows.
sudo supervisorctl stop video_looper or just
stop to stop the video.
sudo supervisorctl start video_looper or just
start to start it up again.
Note that this setup doesn't sync multiple players. Have a look at omxplayer-sync for that.