Why Phonon is a broken wheel
In the discussion the approach taken by the Phonon abstraction layer which the Phonon project is advocating for inclusion in KDE4 also came up. I have held back blogging about Phonon for some time to avoid flamewars, but I don't want to have efforts like OSDL delayed due to setups like Phonon being promoted or thought of as a workable solution for the issues faced. Let me start of with a brief introduction to the area of multimedia frameworks.
First of all multimedia frameworks are very complex systems, handling very hard technical problems in order to cater for issues ranging from problems from dealing with the analog past (for some technical information in this field I recommend fourcc.org), a forest of media formats with different traits, a host of features/deficiencies in hardware and a wide range of other software solutions to interact with like sound servers and legacy systems. On top of this you add performance and latency requirements, network protocols and multiplatform issues. In the end you have a problem space where even those who have worked on the issues for many years need to keep their head clear when designing the framework.
Multimedia frameworks are also by their nature abstraction layers themselves, trying to abstract away all the demuxers, muxers, decoders, encoders, cameras, soundcards, sound systems, network protocols and various types of filters into a coherent and userfriendly API.
Now to get back to why I think Phonon is conceptually broken. First of all it is destined to fall into one of two traps. Either its API become so high level and limited that application developers will shun it due to a lack of features, meaning that you have an API useful for doing 'ding' sounds in standard applications, but anyone wanting more powerful operations will feel its a bigger hindrance than a help. On the other hand if they actually try to implement a feature set that is big enough to at least satisfy a subset, of for instance music player writers, then they will be forced into accessing things so deep in the frameworks that the operations become so framework specific that generalizing them away into a common API will at best be a kludge and at worst produce various broken behaviour changing depending on framework chosen.
Phonon also falls short in many other areas.