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How do I hide an encrypted VeraCrypt volume as a playable video file?
I know I can store the encrypted volume as whatever file type I want, but what if I want that file to act as the file type? For example, if I save it as an mp4 file, how can I open the file in a media player (and it will play something) and open it in VeraCrypt?
With some intermediate steps it works for some video formats.
Many formats allow "trailing garbage", which either causes an error message after the correct video played, causes garbage output or is just ignored.
When you now append your volume to the video, the video still works. To access the volume, you can e.g. use the device-mapper (when using linux) to create a blockdevice from the file, which has some offset (the length of the video) and then use this.
If you only want to hide the volume (e.g. to put it on a usb stick when traveling) but not use it in this form, you just need a program to split the file at the offset, so you can unpack it on the computer where you want to use it.
There are programs which allow to combine images and rar files, which may work with videos as well. So the easiest solution there might be to pack it into a rar and use such a program.
I know you can edit an mp3 file in a hex editor and extend the file with and encrypted. pdf file. The mp3 will still play and you just have to edit the file with the hex editor to extract the pdf. Should be possible with an mp4.
How do I hide an encrypted VeraCrypt volume as a playable video file?
You can't. Or, at least not out of the box.
What you're asking for is termed steganography, or hiding data within data, without revealing that there's a second, embedded message.
Steganography is completely feasible, even in video. But Veracrypt does not support this. It supports hidden volumes, which will not show up as files, but rather as random noise on the drives unallocated parts. It's not perfect, and has severe drawbacks. And it does not allow storing data inside a video file.
What you're asking is feasible. How feasible depends on how well you want to hide it. You want to hide against cursory searches? Appending a TC container to the end of a video will probably work - but this will fail the instant anyone probes the video bit rate and size of the file. To achieve real steganography you want the signal embedded in a way that looks like random noise - and with video that is likely to need some heavy lifting CPU-wise.
