Here’s a good page that explains what I mentioned:
Most of the animation formats (e.g. AVI Jpeg, FFMpeg) are lossy formats and reduce the amount of information in the pictures to reduce the file size. Depending on the exact format and settings, the loss of information may be subtle enough that you don’t notice it or it might result in noticeable artifacts, like blurring, blockiness and strange colour streaking.
For long or complex animations, many people will not render directly to an animation format, but to a series of stills using a lossless format (e.g. png). This gives you much more flexibility for a number of reasons:
- You don’t need to render the entire animation at once.
- You can easily postprocess your rendered frames before assembling them into an animation.
- If your assembled animation suffers from compression artifacts, you can just change some settings and reassemble the pre-rendered frames - you don’t need to re-render the entire scene.
Of course, this may not be the problem at all
Hope this helps, but my apologies if you already knew all of it.