Configure the Video Output
You can configure the firmware’s behavior in many ways using the /boot/config.txt file. It contains all configuration parameters for the Pi’s firmware; it’s a good idea to bookmark their descriptions[53] in your web browser, because sooner or later you’ll probably want to tweak a few things. Using the configuration file, you can adjust video and audio output, and you can even change the CPU’s clock rate.
Most of the defaults work quite well on most systems, but the video output doesn’t always work properly. The main problems are overscan and underscan, especially when you’re using composite video output. In the case of underscan, the video output doesn’t use the whole display size, so you can see a black frame around ...
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