karabiner elements media control keys for keyboards that don't have them eg FILCO TKL

filco-media-keys.json

{
	"title": "Media Controls for keyboards that don't have it",
	"rules": [{
		"description": "Function media keys",
		"manipulators": [{
				"type": "basic",
				"from": {
					"key_code": "insert",
					"modifiers": {
						"mandatory": [
							"fn"
						]
					}
				},
				"to": [{
					"key_code": "play_or_pause"
				}]
			},
			{
				"type": "basic",
				"from": {
					"key_code": "pause",
					"modifiers": {
						"mandatory": [
							"fn"
						]
					}
				},
				"to": [{
					"key_code": "mute"
				}]
			},
			{
				"type": "basic",
				"from": {
					"key_code": "page_up",
					"modifiers": {
						"mandatory": [
							"fn"
						]
					}
				},
				"to": [{
					"key_code": "volume_increment"
				}]
			},
			{
				"type": "basic",
				"from": {
					"key_code": "delete_forward",
					"modifiers": {
						"mandatory": [
							"fn"
						]
					}
				},
				"to": [{
					"key_code": "rewind"
				}]
			},
			{
				"type": "basic",
				"from": {
					"key_code": "end",
					"modifiers": {
						"mandatory": [
							"fn"
						]
					}
				},
				"to": [{
					"key_code": "fastforward"
				}]
			},
			{
				"type": "basic",
				"from": {
					"key_code": "page_down",
					"modifiers": {
						"mandatory": [
							"fn"
						]
					}
				},
				"to": [{
					"key_code": "volume_decrement"
				}]
			}
		]
	}]
}