Query how much bytes can be read from each queued buffer. This means
that the result of this call is the maximum number of bytes that can
be read from each of the pads.
This function should be called with pads STREAM_LOCK held, such as
in the callback.
Query how much bytes can be read from each queued buffer. This means that the result of this call is the maximum number of bytes that can be read from each of the pads.
This function should be called with pads STREAM_LOCK held, such as in the callback.
MT safe.