poor playback quality with *.webm

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http://ubuntuforums.org – I am experimenting with *.webm videos. I've created several *.webm videos using different bit rates and in all cases the playback quality in MythTV FE is poor - highly pixelated. However, when viewing the same videos using VLC player, these videos appear much better (some slight/occasional digital artifacts are apparent but not enough to ruin the viewing experience). I'll admit that my settings to create *.webm are not yet optimized using avconv, but again, VLC plays the videos I've created just fine. Why does the playback quality of *.webm depend on the player? Why are there noticeabl (Hardware)