Recording session & resizing VM window

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Carl Colijn
Posts: 3
Joined: 13. Oct 2017, 20:35

Recording session & resizing VM window

Post by Carl Colijn »

Hi all,

Today I've made a recording of a windowed VM session. During the recording one application didn't fit in the resolution of the window, so I resized the VM window. When later re-watching the resulting video, it turns out it got mangled from the moment on the window was resized.

I was using VirtualBox 5.1.22.r115126 on Windows 10 (fully updated), all 64 bits. The settings for the VM had it produce an video sized at 1024x768, while the VM window was only running at 800x600. This resulted in a fat black border surrounding the inner screen content. From the moment on that I resized the window, the borders remained unchanged, while the inner content got garbled.

So, this 1) is a bug report I assume, but 2) I'd like to know if this can be used to reverse the video mangling in any way? The screen recording I made was of an Indian "Microsoft" security employee trying to hack this VM, failing at that and I think I ended up logging into their machine in the end when I reconnected the remote control software. I saw a nice dashboard-like interface, but got disconnected pretty quickly again. Not too bad since I recorded it anyway, but now it appears I have nothing valuable in the end. Would really like to get this reversed!

All suggestions on what can be done are welcome!
Carl Colijn
Posts: 3
Joined: 13. Oct 2017, 20:35

Re: Recording session & resizing VM window

Post by Carl Colijn »

About the restoring the video: I also posted about this in video dot stackexchange dot com, and got a reply there; see
http://video.stackexchange.com/question ... webm-video
(sorry, can't post links yet with my noob status here :) )

So that reduces this post to just a bug report!
Last edited by socratis on 14. Oct 2017, 22:33, edited 1 time in total.
Reason: Fixed obfuscated URLs.
Carl Colijn
Posts: 3
Joined: 13. Oct 2017, 20:35

Re: Recording session & resizing VM window

Post by Carl Colijn »

Final update: I managed to write a small app to reverse the mangling in the video. I can now confirm that when you start a recording with default settings of 1024x768 pixels, but have a VM window of 800x600 pixels, the result will correctly be the VM window's content with a black border around it.
But if you then widen the VM window while still recording, the now longer scanlines will be streamed into that 800x600 part of the resulting video. The border remains intact and black.

When you then inspect the frames in the now mangled video, you can reconstruct the longer scanlines by unwrapping the lines. However, as I assume there is still a chroma shift in the result, but the value of the pixels will be OK.
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