When the stream can't have its caps detected, better not to expose it.
If no streams are known, signal an error about no playable streams to
the application
Adds basic handling for seek in time events. Needs to cooperate
with the downstream qtdemux so that it forwards the seeks and
the corresponding newsegments
This is important for downstream to properly timestamp the samples
The default value is 10000000, but this can be set in the stream
or at the top-level manifest entry
Keep a ref on pad to prevent it being unreffed while the mssdemux
streams are still using it. Also reset the element when going to
ready instead of when going to null.
Use shorter names for the MSS manifest helper structure and functions.
Also continues the implementation of the stream fetching and pushing loop.
Now it uses the base url correctly and already fetches and pushes the fragments
downstream
