How it works, in detail

This page is for readers who want to know what happens underneath. You do not need any of it to use Two Left Wheels 360. For the short version, see How Two Left Wheels 360 works.

The virtual drive

The virtual drive is provided by Dokan, a Windows driver that lets a program answer file requests itself. Windows shows the drive as a folder. When any program lists it or reads from it, Windows forwards the request to Two Left Wheels 360.

Each recording is presented as a MOV file of uncompressed video with the camera's audio. Uncompressed video has frames of a fixed size, so the position a program reads from says exactly which frame it wants. That is what makes it possible to produce any frame on request, in any order.

Full-resolution frames

When a program reads a full-resolution frame, Two Left Wheels 360 decodes that frame of both lenses from the camera file with the graphics card's video decoder, corrects rolling shutter, applies stabilization and horizon levelling, matches the lenses along the seam, evens out their colour and blends them into one 360° picture. Nothing of this is stored: a stitched 8K file at editing quality would take about 20 GB per minute.

An 8K frame is about 88 MB of uncompressed picture and takes a quarter of a second or more to make on our test computer. That is fine for looking at a frame and for a render, and too slow to play.

8-bit recordings are delivered as 8-bit RGB. 10-bit recordings, such as the Insta360 X6's and the DJI cameras', are stitched from the 10-bit decoded frames and delivered as 10-bit 4:2:2 video, so no precision is lost on the way to your editor.

Proxies: three kinds

Editing happens on proxies, small versions of each clip that play in real time. Two Left Wheels 360 gets them in up to three ways, and your editor sees the same proxy file throughout.

• Stitched live from the camera's proxy. The camera records a low-resolution file beside each recording (LRV or LRF). It holds both lenses, unstitched. Two Left Wheels 360 stitches a proxy frame from it on request in a few milliseconds, so proxies are available the moment you add a recording.
• From a proxy made for you. When the camera's file is missing, Two Left Wheels 360 makes an equivalent one from the original in the background. That takes about as long as the recording plays. Until it is ready, only the full-resolution file is available for that recording.
• From a stitched proxy file. While you already edit on live-stitched proxies, Two Left Wheels 360 stitches each recording's proxy once, in the background, into an ordinary small video file, and switches to it when it is ready. Reading that file needs no stitching and no graphics card, so cuts, clicks and opening your editor's project get faster and the graphics card is left to your editor. On our test computer it is made about two and a half times faster than the recording plays.

Background work waits while your editor is reading frames, and no stitched proxy file is made when the disk has less than 20 GB free.

When you change settings

Full-resolution frames are always made with the editing pack's current settings, because nothing is stored.

A stitched proxy file holds the picture as it was stitched, so it belongs to the settings it was made with. When you change a setting, Two Left Wheels 360 goes back to stitching that editing pack's proxies live with the new settings, at once, and makes new stitched proxy files in the background. You can keep editing throughout. The only difference you may notice is that proxies respond a little more slowly until the new files are ready.

Your editor may keep showing frames it read before the change until it reads them again.

What is stored on your disk

The full-resolution stitched video is never stored. These smaller files are kept in the app's data folder in your Windows user profile, not in your media folders:

• Stitched proxy files: about 8 GB per hour of footage recorded at 24 frames per second, roughly twice the size of the camera's own proxy.
• Proxies made for recordings that came without the camera's proxy file: about the size of the camera's own.
• Prepared audio, the lens colour measurement of each recording and small index files.

They are kept while an editing pack uses them, so that returning to an edit costs no time. Files that no editing pack needs any more are removed automatically, such as stitched proxy files made with settings you have since changed. Proxies made for recordings without the camera's proxy file are kept, because making one again takes as long as the recording plays. When you delete an editing pack, you choose whether its files are removed too. The privacy page says where the folder is and how to remove it.