If the caller passed in "audio_%u" instead of a concrete pad name into
gst_element_request_pad_simple() then the pad name will be NULL. In that case
use the pad template name for requesting the pad from splitmuxsink.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/8697>
The stream was keeping a reference to the sink, preventing
it to be removed properly by the pipleline bin.
Clean up and simplify the code to get the stream from the pad.
Add more mutex protection against add/remove requested pad.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/7916>
Use gst_codec_utils_caps_get_mime_codec() in pbutils for codec
strings. That function gives more elaborate RFC 6381 compatible
strings than the helper functions in gstmdphelper.c, such as
"avc1.F4000D".
Remove the helper functions, as they were only used from dashsink.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/5404>
