How to Flip the Video Output of a Raspberry Pi Using Code

To flip the output of a Raspberry Pi display for use in a teleprompter setup, you will essentially be mirroring the display output so that text appears correctly when reflected off the teleprompter glass. This can be achieved by modifying the display configuration. Here's how you can do it:

Using /boot/config.txt

1. Access the Pi's Configuration File: You'll need to edit the config.txt file found in the /boot directory. You can access this file by connecting to your Raspberry Pi via SSH or by directly editing the SD card on another computer. If you're using SSH or are logged into the terminal directly, you can open the file with a text editor like nano:

   sudo nano /boot/config.txt
   

2. Modify the Display Settings: You're looking to add or modify a line that sets the display orientation. For mirroring the display, you will use the display_hdmi_rotate or display_lcd_rotate setting, depending on your connection type (HDMI or LCD). The value you set will determine the rotation and mirroring effect:

   • To mirror horizontally (flip left to right), you would use:

     display_hdmi_rotate=0x10000
     

     or for LCD:

     display_lcd_rotate=0x10000
     

   • To mirror vertically (flip top to bottom), you would use:

     display_hdmi_rotate=0x20000
     

     or for LCD:

     display_lcd_rotate=0x20000
     

   Note: These settings are for newer versions of Raspberry Pi firmware. If you find that these settings do not work, you may need to update your Raspberry Pi's firmware or use alternative methods such as modifying the software that runs your teleprompter to flip the text.

3. Save and Reboot: After adding the necessary line, save the file and exit the text editor. If you're using nano, you can do this by pressing Ctrl + X, then Y to confirm the changes, and Enter to save. Afterward, reboot your Raspberry Pi for the changes to take effect:

   sudo reboot
   

Using Command Line (Temporary)

For a temporary solution that doesn't require a reboot or changing system files, you can use the xrandr command. This is useful if you're running a graphical desktop environment:

xrandr --output HDMI-1 --reflect x

Replace HDMI-1 with your actual display output name (you can find it by just running xrandr without arguments). This command flips the display horizontally. For vertical flipping, you might use --reflect y, though support for these options can vary based on the display driver and configuration.

Final Note

Keep in mind that flipping the display might not be supported in all configurations, especially if you're using certain custom displays or older versions of Raspberry Pi OS. If the above methods do not work, consider updating your system or looking into software-based solutions within your teleprompter application to achieve the mirrored effect.