Keep state variable to enumerate things. This allows us to remove the
expectation that the same index will give the same item.
Use a new rectangle type for video size. When enumerating sizes, this
allows us to specify relations between width and height more easily.
Remove the struct and bytes type, they are like pointer.
Add filter to enum_formats to speed up enumerations.
Remove the thread from alsa sink and use the pollfd event.
Make it possible to pass multiple fds in one pollfd event
Add 3 callbacks to the pollfd event and add support for timeouts
