This section of the appendix will discuss shortly what changes to plugins will be needed to quickly and conveniently port most applications from &GStreamer;-0.8 to &GStreamer;-0.9, with references to the relevant sections in this Plugin Writer's Guide where needed. With this list, it should be possible to port most plugins to &GStreamer;-0.9 in less than a day. Exceptions are elements that will require a base class in 0.9 (sources, sinks), in which case it may take a lot longer, depending on the coder's skills (however, when using the GstBaseSink and GstBaseSrc base-classes, it shouldn't be all too bad), and elements requiring the deprecated bytestream interface, which should take 1-2 days with random access. The scheduling parts of muxers will also need a rewrite, which will take about the same amount of time. Most functions returning an object or an object property have been changed to return its own reference rather than a constant reference of the one owned by the object itself. The reason for this change is primarily threadsafety. This means, effectively, that return values of functions such as gst_element_get_pad (), gst_pad_get_name () and many more like these have to be free'ed or unreferenced after use. Check the API references of each function to know for sure whether return values should be free'ed or not. In 0.8, scheduling could happen in any way. Source elements could be _get ()-based or _loop ()-based, and any other element could be _chain ()-based or _loop ()-based, with no limitations. Scheduling in 0.9 is simpler for the scheduler, and the element is expected to do some more work. Pads get assigned a scheduling mode, based on which they can either operate in random access-mode, in pipeline driving mode or in push-mode. all this is documented in detail in . As a result of this, the bytestream object no longer exists. Elements requiring byte-level access should now use random access on their sinkpads. Negotiation is asynchronous. This means that negotiation is, downstream, done as data comes in and, upstream, as renegotiation is required. All details are described in . For as far as possible, elements should try to use existing base classes in 0.9. Sink and source elements, for example, could derive from GstBaseSrc and GstBaseSink. Audio sinks or sources could even derive from audio-specific base classes. All existing base classes have been discussed in and the next few chapters. In 0.9, event handling and buffers are separated once again. This means that in order to receive events, one no longer has to set the GST_FLAG_EVENT_AWARE flag, but can simply set an event handling function on its sinkpad(s), using the function gst_pad_set_event_function (). The _chain ()-function will only receive buffers. Although core will wrap most threading-related locking for you (e.g. it takes the stream lock before calling your data handling functions), you are still responsible for locking around certain functions, e.g. object properties. Be sure to lock properly here, since applications will change those properties in a different thread than the thread which does the actual data passing! You can use the GST_LOCK () and GST_UNLOCK () helpers in most cases, fortunately, which grabs the default property lock of the element.