48 lines
2.0 KiB
Markdown
48 lines
2.0 KiB
Markdown
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# slitscan
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slitscan is a script inspired by [this Mastodon
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post](https://fed.qaz.red/@elithebearded/113070315634312301). It takes a video
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file as input and allows you to "transpose" the frames of the video to view
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along the height or width axes instead of the "time" axis you normally watch a
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video along.
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## Usage
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Say you have a video file `foo.mkv`. To transpose along the height axis and save
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to `bar.mkv`, run
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```
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python slitscan.py foo.mkv bar.mkv --height
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```
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Similarly, to transpose along the width axis, run
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```
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python slitscan.py foo.mkv bar.mkv --width
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```
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## Details
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### Uh... what does this do?
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Check the linked post for another explanation and examples.
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To elaborate, you can think of a video as a 3D array of pixels. Say the axes of
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the array are the frame, height, and width, in that order. Then the entry (24,
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500, 900) gives you the pixel in the 499th row and 899th column of the 23rd
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frame of the video (we're 0-indexed). You can imagine "watching" a video as
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just iterating through the frame axis of that array and displaying each 2D
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slice.
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This program transposes that 3D array so you're instead iterating over the
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height or width axis and displaying *those* 2D slices. For instance, if you
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transpose along the height axis, then the first frame of the output video
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consists of the top row of pixels of every single frame of the original video.
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The second frame is then the second row of every single original frame, and so
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on. Instead of viewing each original frame one by one, it's like you're viewing
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them all at once, but only one horizontal line of pixels at a time.
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### But why?
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The author of that Mastodon post mentioned that he wrote a bash script to do
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this that took a *a couple of days* to run for a short clip. I wanted to see if
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I could make it faster (and I did - this runs on the order of a few *minutes*
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for similarly short clips). It might be possible to make this script even
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faster, but I couldn't figure out how without the script using too much memory.
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### Is this even useful?
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I would love to find out that it is!
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