Today, (don't go for orangepi) there are many other SBCs in the 35$ range which have both video in and out with h264 and some with h265 hardware compress and decompress capabilities which run linux or android.
Also, even cheaper 5GHz WiFi dongle HDMI in and out transmitters and receivers exist, but, you wont have the compression protocol & compression level settings and large memory video caching and more advanced standard network compliant WiFi capabilities of the SBCs, but they will be half price.
Also, for the SBCs, you can do a whole lot more, like remote desktop, have Ethernet & WiFi & Bluetooth. Audio and Video & Mic inputs and outputs and a lot more.
If you want frame by frame, just use I-Frame only compression mode in h264, but, be aware that your bitrate will be 50 megabits for 1080p. (You can expect at least 8 megabits for 480p) Or, set your I-Frame interval forced to every 2nd frame and disable advance features like multiple I-Frames and bidirectional encoding which will cut that almost in half, but, make super fast error recovery and stream reconnects and file seeking. You can do the same for MJPEG and expect high bitrates as well. The advantage here is super quick recovery from bit errors or broken streams/stream reconnects. Also include the feature for extra ancillary data for video editing. It only adds a % or 2% on the total bitrate, but, allows quick recovery from biterrors and quick seeking within a stream.
Use .mp4 when delivering a final complete file, but if you will be streaming, the industry typically uses .ts which has info in it to deal with broken/corrupt data streams and disconnect/reconnect.
Almost all FPGA/Dedicated IC compressors/decompressors will deliver you a transport stream. It is your computer's job to package the part of the stream you want into a .mp4 container, which means identifying the amount of time and data in that package and trimming the source data to the valid splicing/cut points. You may need to also add index data into the .mp4 file & close it up before transmitting the file.