Reverse-engineering the dynamic wallpaper file format in macOS Mojave.

Mojave-dynamic-wallpaper-notes.md

The dynamic wallpaper in MacOS Mojave is a single 114 MB .heic file that seems to contain 16 embedded images.

It also contains the following binary plist data in its metadata under the key "Solar". It's an array of 16 items, each with four keys:

• i (integer). This seems to be the image index.
• o (integer). This is always 1 or 0. Stephen Radford thinks it indicates dark mode (0) vs. light mode (1).
• z (decimal). Time of day in degrees?
• a (decimal). Solar hour angle?

Solar.plist

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
	<key>si</key>
	<array>
		<dict>
			<key>i</key>
			<integer>0</integer>
			<key>z</key>
			<real>270.9334057827345</real>
			<key>a</key>
			<real>-0.3427528387535028</real>
			<key>o</key>
			<integer>1</integer>
		</dict>
		<dict>
			<key>i</key>
			<integer>1</integer>
			<key>z</key>
			<real>81.77588714480999</real>
			<key>a</key>
			<real>-10.23975864472505</real>
			<key>o</key>
			<integer>1</integer>
		</dict>
		<dict>
			<key>i</key>
			<integer>2</integer>
			<key>z</key>
			<real>86.33545030477751</real>
			<key>a</key>
			<real>-4.247734408075456</real>
			<key>o</key>
			<integer>1</integer>
		</dict>
		<dict>
			<key>i</key>
			<integer>3</integer>
			<key>z</key>
			<real>90.81267037496195</real>
			<key>a</key>
			<real>1.389086633100843</real>
			<key>o</key>
			<integer>1</integer>
		</dict>
		<dict>
			<key>i</key>
			<integer>4</integer>
			<key>z</key>
			<real>95.30740958876589</real>
			<key>a</key>
			<real>7.167168970526129</real>
			<key>o</key>
			<integer>1</integer>
		</dict>
		<dict>
			<key>i</key>
			<integer>5</integer>
			<key>z</key>
			<real>99.92062963268938</real>
			<key>a</key>
			<real>13.08619419164163</real>
			<key>o</key>
			<integer>1</integer>
		</dict>
		<dict>
			<key>i</key>
			<integer>6</integer>
			<key>z</key>
			<real>129.1865220819196</real>
			<key>a</key>
			<real>40.41563946490428</real>
			<key>o</key>
			<integer>1</integer>
		</dict>
		<dict>
			<key>i</key>
			<integer>7</integer>
			<key>z</key>
			<real>182.2330942549791</real>
			<key>a</key>
			<real>53.43347266172774</real>
			<key>o</key>
			<integer>1</integer>
		</dict>
		<dict>
			<key>i</key>
			<integer>8</integer>
			<key>z</key>
			<real>233.5515919580959</real>
			<key>a</key>
			<real>38.79312820063863</real>
			<key>o</key>
			<integer>1</integer>
		</dict>
		<dict>
			<key>i</key>
			<integer>9</integer>
			<key>z</key>
			<real>261.8715904657666</real>
			<key>a</key>
			<real>11.08942317126588</real>
			<key>o</key>
			<integer>1</integer>
		</dict>
		<dict>
			<key>i</key>
			<integer>10</integer>
			<key>z</key>
			<real>266.4432737071051</real>
			<key>a</key>
			<real>5.184575323673625</real>
			<key>o</key>
			<integer>1</integer>
		</dict>
		<dict>
			<key>i</key>
			<integer>11</integer>
			<key>z</key>
			<real>275.4420453669525</real>
			<key>a</key>
			<real>-6.248309374122789</real>
			<key>o</key>
			<integer>1</integer>
		</dict>
		<dict>
			<key>i</key>
			<integer>12</integer>
			<key>z</key>
			<real>280.0703158940117</real>
			<key>a</key>
			<real>-12.20770735214888</real>
			<key>o</key>
			<integer>1</integer>
		</dict>
		<dict>
			<key>i</key>
			<integer>13</integer>
			<key>z</key>
			<real>309.4185731874514</real>
			<key>a</key>
			<real>-39.48933951993012</real>
			<key>o</key>
			<integer>0</integer>
		</dict>
		<dict>
			<key>i</key>
			<integer>14</integer>
			<key>z</key>
			<real>2.175096553867547</real>
			<key>a</key>
			<real>-52.75318137879935</real>
			<key>o</key>
			<integer>0</integer>
		</dict>
		<dict>
			<key>i</key>
			<integer>15</integer>
			<key>z</key>
			<real>53.50908581251309</real>
			<key>a</key>
			<real>-38.04743388682423</real>
			<key>o</key>
			<integer>0</integer>
		</dict>
	</array>
</dict>
</plist>