Josef, You could convert the ts files to mp4 using VLC
https://www.youtube.com/watch?v=6SOKiuAPiao

For images: jpg [jpeg] is a lossy format -- more data is lost as the quality setting is decreased -- but because data is discarded it offers the smallest files. Png is lossless but optimized & has the option of saving an alpha [transparency] layer. Tif [tiff] is lossless, can save multiple layers, can use higher bit depths, and is most used for works in progress. It can use lzw compression. Bmp is more often ignored as not bringing anything to the table. Generally you'll get extremely similar if not identical results converting/saving to one of these formats in most software. Resizing is a different matter... you will lose quality, the best way to do it currently is using specialized AI, there are 1/2 dozen or so algorithms, e.g., bi-cubic, and which one is used for a particular resizing operation can effect quality, sometimes a lot.

Video is a completely different matter. Original footage may store complete frames [great for editing], though in a different format than still images. Most compression uses key frames, with those frames in between storing just the changes between key frames. The way that data is analyzed & stored varies with the compression standard, e.g., AVC. (Re)encoding Always loses quality, as does resizing, though often less than from encoding. File size is determined by the frame size, frames per second, type of compression [AVC etc.], amount or level of compression, most often referred to as the bit rate, and the encoder settings. Quality is determined by the original quality, and by the hardware used -- GPU is faster than CPU but most always effects quality negatively. It's also determined by the type & amount of compression, and by the encoding settings, which can be quite extensive and hidden from the user in apps like the Geekersoft Compressor. Note that when/if compressed video is (re)encoded, it also must be reconstructed in the same way a player would to display each frame, and then that's what's analyzed and encoded. GPU vs. CPU matters there too. When it comes to speed (re)encoding, GPU can be faster than CPU, CPU brand/model, speed, & number of cores matters, bouncing from one SSD [preferably NVMe] to another is faster, the encoder software can be faster, and the encoder settings can make a huge difference, e.g., highest quality 2 pass may take 24 hours+. That said, most of these apps use ffmpeg code libraries, so the encoder software itself is generally the same.

Hi Martin. This is going to blow your mind, but here's how to do it.
Change the PowerPoint file extension from .pptx to .zip
The file will now be a Zip file.
Open it, and open the folder PPT, then open the folder Media
All you media files - images, videos, etc, will be in here
You can then extract them, compress them, and reaplace the existing files with the new compressed files
Then change the file extension back to .pptx.
You can do the same with Word files

Joel Malach, That does blow my mind. Zipping a powerpoint just be changing the file extension to zip. I was skeptical but copilot said it was true, advising to "make a backup just to be safe".