It might be a second stream collection that we receive at a later time,
and the previous pads would already be unblocked at that point. So block
all currently unblocked pads again and then adjust the offset
according to the new situation.
This fixes playback of various RTMP streams where usually we first get a
stream collection with only one of the two streams, and shortly
afterwards with both streams.
This works as an alternative to the "uri" property, which would use an
`uridecodebin3` element.
The provided source element can have static audio/video pads or provide
them as sometimes pad while signalling no-more-pads or a stream
collection message once all pads are available.
They were already converted to the running time a few lines above and
updated inside the buffer. Converting another time for the timeout
causes the timeout to happen at the wrong time, usually much later than
it should.
This is a wrapper around uridecodebin3 and fallbackswitch that allows to
switch to a still frame on errors and automatically retries the source
in the background on errors until a given retry timeout is reached.
