Encoder Options for WEBM Files
WEBM files are saved using VP8 compression.
Video Bitrate - VP8 or VP9 compressor
Here you specify the bitrate the video is encoded at. The higher the value, the better the quality of the picture and the less artifacts (macro blocks and blurring). You should experiment with this setting. Please note, higher values result in a larger file size.
Average bitrate is the mean bitrate, and is the main value that affects quality. Maximum bitrate should generally exceed this, but no set margin is required; the Average and Maximum bitrate can safely be the same.
Maximum bitrate is the absolute maximum. It does not majorly affect quality but some formats have set values that must not be exceeded (e.g., 10 megabits for DVD video). Sometimes if your maximum bitrate is too low, you will get macro block effects, in which case you should decrease both values.
WEBM files are saved using Vorbis compression for sound.
Quality (Ratefactor) - Vorbis compressor
Here you specify the quality rate which will be used by the Vorbis audio compressor. The higher the value, the better the quality of sound. Please note that higher values result in a larger file size. You should experiment with this setting to pick the optimal quality for your needs.