Quality and compression
Digital video can be compressed to use less bandwidth for streaming and to save storage space. Compression involves applying a mathematical algorithm to the numerical values that make up the video stream. The output is considerably smaller than when not compressed, but the video stream must also be expanded by a reversing algorithm before it can be viewed.
Most algorithms or codecs (an abbreviation for compressor/decompressor) achieve this partly by discarding information of little significance. During decompression, this missing data is restored by approximation, making the end result slightly different than the original recording. This is called lossy compression, as it does actually lower the image fidelity. At low compression ratios, the human eye will not notice this loss, but at higher compression ratios (for low bandwidth), the image quality will deteriorate, with noticeable artifacts in the image.
Different scenes can be compressed with varying results. A busy scene with a lot of motion will be more complex to compress, which results in more bandwidth being required, or an increase in image artifacts. You will need to tweak your compression settings until you find an acceptable trade-off between file size and image quality.
Choosing the right camera and lens for the job will have the greatest effect on image quality, but you can also accomplish a lot through proper positioning and setup of your camera.