If the bitrate is too low, or if the scene features fast movement, flashing lights, or heavy smoke, the encoder runs out of data to accurately describe the image. The result is a pixelated "mosaic" pattern where fine details should be. How to Reduce Mosaic Artifacts and Re-Encode
If is irreparably damaged, consider:
A VMAF increase from <70 to >85 indicates successful mosaic reduction. -Reducing Mosaic-SSIS-586 .720p-DS-.mp4