Why are AV manufactures unable to do this (cost/licence/copyright...etc)?
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Because they don't include video playback capabilities. The reasoning may have smething to do with the complexities of including the required codecs and having to maintain them over the lifespan of an AV receiver? Only Sony have ever included the ability for an AV receiver to play video files using an inbuilt media player. They included this ability onboard a few of their flagship models, but subsequently dropped the ability and no longer include it with any of their present day models.
Technically speaking, an AV receiver only includes the ability to play audio files as a bonus. The primary role of an AV receiver is to process and amplify the audio while acting as a video and source switch. They are not marketed as being media players and you'd get far more support for both audio and video formats by using an external dedicated media player.