it8951-video

Play videos on IT8951-controlled e-paper displays via USB. This has been tested with a Waveshare 7.8inch e-Paper HAT display.

Design

This runs fairly smooth considering it is a e-Paper display (~5 fps) which has not been optimized for video usage. The following "tricks" have been used:

• Convert every video frame into an image which only contains black or white pixels (via dithering)
• Pack pixel information for every frame into 1bit (black = 0, white = 1) and store it in a file so it can be played later (don't do this on-the-fly as the dithering process takes too much time)
• Activate undocumented 1bpp (1 bit per pixel) and "pitch" mode on IT8951 by flipping the bits in the 0x1800_1138 register before displaying
• Store frame data via "fast write" (fw) 0xa5 command in memory
• Since the data is smaller now (322944 bytes) than grayscale images we can store up to 8 frames in the image buffer (which usually only has space for one image)
• Always write in A2 mode since it is fast and does not cause any flashing with b/w-only data. Use GL16 mode sometimes, just to make sure the ghosting does not minder the quality too much

Requirements

• ffmpeg
• Rust

Preparation

In order to make this work you need to create a udev rule that gives users permission to talk to this device. To this end add a file 60-it8951.rules to the /etc/udev/rules.d directory with the following contents:

SUBSYSTEM=="usb", ATTRS{idVendor}=="048d", MODE="0666"

This gives applications access to talk to devices by vendor "048d", which is the IT8951. You can then restart your system, or by write this to trigger without reboot:

udevadm control --reload-rules && udevadm trigger

Usage

Play videos on IT8951-controlled e-paper displays

USAGE:
    it8951-video [OPTIONS] <input>

FLAGS:
        --help       Prints help information
    -V, --version    Prints version information

OPTIONS:
    -v, --vcom <vcom>        VCOM value [default: -1.58]
    -g, --ghost <ghost>      Paint in GL16 mode every nth frame [default: 32]
    -t, --take <take>        Only take every nth frame from video [default: 5]
    -w, --width <width>      Width of video on display [default: 1856]
    -h, --height <height>    Height of video on display [default: 1392]

ARGS:
    <input>    Video file which will be displayed

Credits

• @bspth for finding almost every hack which made this work at all
• https://github.com/faassen/rust-it8951 for the SCSI over USB communication with IT8951