Hi Sophia,
I would recommend trying to compress the video yourself before inserting it into Storyline. That may not stop Storyline from compressing it again, but it may minimize what Storyline does to alter your video.
According to this link (Storyline 360: Streaming Video - Articulate Support), Storyline uses MP4 for really short videos or when the publishing setttings are set to "Static," and MPEG-2 when the publishing settings are set to "Adaptive."
I would recommend trying to compress videos that are more than 2 seconds into a smaller MPEG-2 container before inserting them into Storyline. That way, if I'm not mistaken, Storyline will still try to compress the video, but since it is in the same container that Storyline already wants, the compression will be lessened and the change minimized.
You can compress your own videos using software like Adobe Media Encoder or Handbrake. Perhaps you could try compressing one of your videos into a smaller size and into an MPEG-2 container and see if it still looks okay and not oversaturated. If it does, then try importing it into Storyline and keep the publishing setting to adaptive and see if it changes.
Otherwise, you could try setting the storyline settings to Static and compressing your videos into smaller MP4 videos and then putting them into Storyline. This may work, too, provided your learners have a solid internet connection and the videos will play back smoothly.
Perhaps by compressing the videos yourself into the container that Storyline will end up using will minimize the change to the video that Storyline makes through its own compression.
