Instead, setting quality flags indicates the use of a variable bitrate. Note that with both the audio and video, setting flags for bitrate ( -ab for audio, -b for video) makes little or no difference. Obviously you should adjust this to whatever’s best for your circumstances, but I’ve found 25 to be a good starting point. In other words, a higher qmax means higher compression, which results in lower quality and smaller file size. Setting qmax effectively controls the maximum compression that will be applied to each frame. In my tests, setting qmin makes no difference so I ignore it. With the libvpx library used for WebM, this is actually a quantization level, set with the -qmin and -qmax flags ranging from 0 to 51. Like the audio, we can specify a quality level. Moving on to the video quality and thankfully it’s nice and simple. mono (1) and stereo (2), is controlled with the -ac flag. I’ve found 4 or 5 to be more than adequate.

The quality can be adjusted with the -aq flag from -1 to 10 with a higher number meaning better quality. In later versions the audio codec is Ogg Vorbis by default but personally I specify it just in case. Concentrating on the audio first, we should specify the audio codec which for WebM is Ogg Vorbis: -acodec libvorbis

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