On the first partition of your SD card, you will find a file named config.txt. This file allows you to tweak a lot of things like framebuffer resolution, overclocking, audio, and is documented here
Some TVs send a wrong EDID saying that HDMI audio is not supported while in fact it is. You may need to force HDMI audio by uncommenting this line in the config.txt:
hdmi_drive=2
If your RPi is not booting while using an HDMI to DVI adaptor, please remove this line from your config.txt:
hdmi_drive=2
If you are using a HDMI to VGA adaptor on a Raspberry Pi 1 or 2 and you want to use the jack output for the sound you have to write in config.txt on the first partition of the SD card:
hdmi_ignore_edid_audio=1
So the board’ll not use the HDMI sound output.
Since Lakka version 3.5.1 it is possible to use CRT output. Here are examples for 240p mode:
Add video=Composite-1:720x480@60e to cmdline.txt right after quiet (separate these statements with a space).
Staring from Lakka 4.0 add following line to config.txt:
dtoverlay=vc4-kms-v3d,composite=1
Add video=Composite-1:720x480@60e to cmdline.txt right after quiet (separate these statements with a space).
Add following lines to config.txt:
enable_tvout=1
dtoverlay=vc4-kms-v3d-pi4,composite=1
If you are missing the audio output device for the 3.5 mm jack, following lines have to be added to config.txt to enable audio output via the 3.5 mm jack:
dtoverlay=piaudio
dtparam=audio=on
These lines must be in this order and no other config lines should be between them.
In RetroArch set the audio output device to default:CARD=Headphones to route the audio output to the 3.5 mm jack.