Hi HN, I'm Oskar, a solo indie Mac developer from Sweden. For those in the Mac community, you might know me from my other apps like Sensei and Trim Enabler.

For years, I've been frustrated by the lack of customisation of macOS. In particular the Lock Screen which supports animated wallpapers, but only ones provided by Apple. There's never been a way to add your own personal videos.

I decided to figure out how to solve this, and the result is Backdrop 2.0. Backdrop is my Live Wallpaper app for Mac, it can play video wallpapers on your desktop. And now it can play on your Lock Screen too.

The core technical challenge, as you can imagine, came from trying to do something that Apple otherwise does not allow. However, through extensive reverse engineering of the macOS wallpaper system, I figured out a way to provide Backdrop wallpapers to the system in a way that allows them to play on the lock screen, and even appear in a custom section in System Settings.

I'm here all day to answer any questions—especially about the reverse engineering process, the challenges of integrating with macOS, or the experience of being an indie Mac developer.

Would love to hear your thoughts and feedback.

Worth mentioning that if you want a free way to do this that does not require running additional software.

All you have to do is have a video you want to use, download one of apple's through settings, go to the location of the downloaded background (I don't remember where that is right now but a quick google search would take care of this), rename your file to the name of apple's file and then replace it.

Mac will act as if this video is the right video and use it without complaints. Until apple starts doing any checksum checks on these files I doubt this method will break anytime soon.

This has been working flawlessly for me for a while now.

This may take some finagling to make sure that your video file is not so large that your Mac can't handle it and that you are using the right format. But it is not hard to do.

> The core technical challenge, as you can imagine, came from trying to do something that Apple otherwise does not allow

I think the main question most would ask is what affordances can you give or details you can share to prove that this will continue working in future versions of the os since the foundations seem brittle.

I use Wallpaper Engine on windows for one purpose mostly to avoid burn in since my monitors are always on but I've grown to like it over the years and would like to try something on mac but would hate to purchase software that stops working or future update comes with a readme of how to "re-enable" it.

To me it's a bit too expensive for what it provides, so I'll probably not buy it. However I must agree that the hacks on the internet with renaming videos doesn't work very well, and I like the product, so I still wanted to say congratulations, well done.

What's reverse engineering like on a Mac? Have you ever written about it? I had a lot of experience reverse engineering things on windows (win32 + x86, before 64bit was a thing) using OllyDbg and patching binaries and/or (ab)using dlls. If I had to use windows again and wanted to customize something, I'd probably use windhawk nowadays [0].

On Linux, I can just compile software myself if I need to make changes. But usually most software is configurable enough that I don't need too.

On OSX, I feel like I'm helpless. I've found very little people writing about their experiences, the tools they use, their workflows, the reverse engineered data structures etc. Can you share how you approached this?

The fact that title bars on OSX aren't a fixed size drives me crazy every single day. I looked into it briefly and realized somehow everything I know about other platforms is basically useless.

[0] https://windhawk.net/

This is awesome, nice work!

Next, can you please reverse engineer spaces (multiple desktops) so we can rename them? Desktop 1, Desktop 2 etc is not very useful.

I really like the wallpaper that plays on the top of your website. Can't seem to find it on the app. Could you point me in the right direction? https://cindori.com/backdrop

Hi Oskar - I'd love to propose a product idea to you, i'd love to buy something like this or the Mac if it were available. I had this on my linux laptop (https://man.archlinux.org/man/xtrlock.1.en) but it is surprisingly difficult to find for Macs -- something that locks the computer but still allows you to see the screen. This would be ideal for log windows, dashboards, etc.

Separately, if there is something like this already from a reputable MacOS appstore ecosystem i'd appreciate knowing about it from anyone.

Hi Oskar! In case you want ideas for future apps for later. https://replacicon.app/ replaces Dock icons...but somehow it doesn't work with the warp.dev icon. I wrote the support and I'm paid customers but they never answered. I really dislike all these AI icons are in black and white! They are very hard to tell apart from each other.

What were some of the technical challenges you experienced while reverse-engineering the wallpaper system? I've been reverse-engineering (for lack of a better term) some of macOS' and Xcode's poorly-documented functionality prototyping a personal developer tool. My investigation isn't sophisticated by any means; it's just been trial-and-error, but I haven't found much online in the way of resources for people going down this route.

Very cool and nice solution. I personally need to have a grey background though, no photos etc. Elaborate colors are just overstimulation.

I'm pretty sure I do this on my mac using Aerials. Is your way different from this?

https://aerialscreensaver.github.io/

I like this and would seriously consider buying it - except that the purchase page only has prices in something called "AA$". I have no idea what currency that refers to (AA is Aruba, but they don't use dollars), or how much that might come to in my local currency.

Hi cindori, I couldn't figure these out without purchasing:

1. Does Backdrop plan to support 5K/6K wallpapers? Those resolutions are pretty standard for Mac workstations.

2. Is functionality similar to TopNotch supported where the notch is hidden? If this was supported I'd likely buy a lifetime license today.

Hi Oskar,

I'm a big fan of TrimEnabler since my Hackintosh days. Sensei looks great but since I already have iStat and thought buying another status menu app would be redundant. But I admire the way it looks.

Does the fact that Backdrop reverse engineers the lockscreen mean that it will never come to the App Store?

And where can you pull

The nice thing about an walled garden OS is it functions beautifully, as those in control restrict everything. Only the most trusted programs receive limited control of the OS.

The bad thing about an walled garden OS is you can't change your wallpaper without breaking the rules.

What happens to purchasers if/when apple update MacOS and this no longer works?

Awesome stuff !

I've been trying to make a library/cli to set the wallpaper/screensaver to use in the next version of Aerial (https://github.com/AerialScreensaver/PaperSaver) on individual screens and been toying around a lot with that whole WallpaperAgent subsystem (and obviously everything Aerial like the manifests, etc, before that), so I may have some insights/questions if you have time ?

From what I've seen there are multiple parts to the way that macOS subsystem works :

- Apple fetches the manifest (json file) with their own videos in (only) 240FPS

- It gets ingested in '/Library/Application Support/com.apple.idleassetsd/Aerial.sqlite' for some reason

- Apple pulls the videos in '/Library/Application Support/com.apple.idleassetsd/Customer/4KSDR240FPS' but renames them through a UUID (despite them having individual keys in the JSON)

Adding videos and sections in System Settings, you can do by manipulating that sqlite and killing WallpaperAgent (or maybe something else) before doing it, but as far as I remember (I only toyed with that part last year during Sequoia beta, so probably misremembering), macOS will periodically pull the manifest again and (fairly often) erase all your changes.

As far as I know, what you select then gets saved per screen/space in `~/Library/Application\ Support/com.apple.wallpaper/Store/Index.plist` (with a lovely Base-64 coding thrown in for fun).

The last part to this is a SystemWallpaperURL key stored in `~/Library/Preferences/com.apple.wallpaper.plist` which I believe (not 100% sure), contains the "special" video that gets played on a cold boot login (as far as I know it's a separate state from the "classic" Lock Screen).

So if I may :

- Do your videos show up on a cold boot too (that separate state I mentionned?) or just the "classic" Lock Screen? My rough guess is the cold boot lock screen can only display videos that are on the System Volume that's mounted before the user volume, so that one is probably fully out of reach.

- How hard did you have to workaround working with restricted paths ? Apple (for some good reasons) restricts hard access to files in user folders, and at that point the only safe place I can reasonably find (outside of containers, but that's a whole other story with screensavers) is `/Users/Shared`. Are you using that folder too?

- Are you messing with the sqlite db, or are you injecting via a reversed engineered api?

- Did you try editing `~/Library/Application\ Support/com.apple.wallpaper/Store/Index.plist` to set your video wallpapers or are you just relying on them being integrated in System Settings?

Since Sequoia, right now Apple broke the way we could set a screensaver via terminal. I got that part working (setting per screen/space) in PaperSaver, but the wallpaper part (basically just switching to another user selected image, not even a video, but this has to be done per space for which we don't have a public api for), I can't seem to get quite right yet, so any insight you have on that would be welcome. Take care and again awesome effort on your launch, this is a non trivial system with so many pitfalls, it takes a bunch of dedication to make it work with so many subtle problems in every corner.

$45 or a monthly subscription for a feature that should be possible out of the box. I will simply never understand the allure of Apple products.

Is this inspired by that viral Sabrina Carpenter lock screen video?

https://github.com/sindresorhus/Plash

If you're going through so much trouble to reverse engineer macOS to customize it in a non-standard way, why even bother staying in the Apple walled prison. Why not just use Linux at that point? You can customize it to your heart's desire.