add some more methods to the Pipeline object, clean up docs

go.mod

@@ -6,5 +6,6 @@ require (
 	github.com/gotk3/gotk3 v0.4.0
 	github.com/mattn/go-pointer v0.0.1
 	github.com/spf13/cobra v1.0.0
+	github.com/tinyzimmer/go-gst-launch v0.0.10 // indirect
 	golang.org/x/net v0.0.0-20190522155817-f3200d17e092
 )

go.sum

@@ -86,6 +86,8 @@ github.com/spf13/pflag v1.0.3/go.mod h1:DYY7MBk1bdzusC3SYhjObp+wFpr4gzcvqqNjLnIn
 github.com/spf13/viper v1.4.0/go.mod h1:PTJ7Z/lr49W6bUbkmS1V3by4uWynFiR9p7+dSq/yZzE=
 github.com/stretchr/objx v0.1.1/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
 github.com/stretchr/testify v1.2.2/go.mod h1:a8OnRcib4nhh0OaRAV+Yts87kKdq0PP7pXfy6kDkUVs=
+github.com/tinyzimmer/go-gst-launch v0.0.10 h1:KyHnaqabbBtAyr7WADBeUrfLDH6H2tpqdVoNew1sSZc=
+github.com/tinyzimmer/go-gst-launch v0.0.10/go.mod h1:OrGpiXW8hHT7r18jCku5Tc/RDArJYhOpQY85M5RFXTU=
 github.com/tmc/grpc-websocket-proxy v0.0.0-20190109142713-0ad062ec5ee5/go.mod h1:ncp9v5uamzpCO7NfCPTXjqaC+bZgJeR0sMTm6dMHP7U=
 github.com/ugorji/go v1.1.4/go.mod h1:uQMGLiO92mf5W77hV/PUCpI3pbzQx3CRekS0kk+RGrc=
 github.com/xiang90/probing v0.0.0-20190116061207-43a291ad63a2/go.mod h1:UETIi67q53MR2AWcXfiuqkDkRtnGDLqkBTpCHuJHxtU=

gst/gst_element.go

@@ -9,7 +9,6 @@ package gst
 import "C"
 
 import (
-	"errors"
 	"fmt"
 	"unsafe"
 
@@ -54,13 +53,24 @@ func (e *Element) LinkFiltered(elem *Element, caps *Caps) error {
 	return nil
 }
 
-// GetBus returns the GstBus for retrieving messages from this element.
-func (e *Element) GetBus() (*Bus, error) {
+// GetBus returns the GstBus for retrieving messages from this element. This function returns
+// nil unless the element is a Pipeline.
+func (e *Element) GetBus() *Bus {
 	bus := C.gst_element_get_bus((*C.GstElement)(e.Instance()))
 	if bus == nil {
-		return nil, errors.New("Could not retrieve bus from element")
+		return nil
 	}
-	return wrapBus(glib.Take(unsafe.Pointer(bus))), nil
+	return wrapBus(glib.Take(unsafe.Pointer(bus)))
+}
+
+// GetClock returns the Clock for this element. This is the clock as was last set with gst_element_set_clock.
+// Elements in a pipeline will only have their clock set when the pipeline is in the PLAYING state.
+func (e *Element) GetClock() *Clock {
+	cClock := C.gst_element_get_clock((*C.GstElement)(e.Instance()))
+	if cClock == nil {
+		return nil
+	}
+	return wrapClock(glib.Take(unsafe.Pointer(cClock)))
 }
 
 // GetState returns the current state of this element.
@@ -130,15 +140,6 @@ func (e *Element) GetPadTemplates() []*PadTemplate {
 	return out
 }
 
-// GetClock returns the clock for this element or nil. Unref after usage.
-func (e *Element) GetClock() *Clock {
-	clock := C.gst_element_get_clock((*C.GstElement)(e.Instance()))
-	if clock == nil {
-		return nil
-	}
-	return wrapClock(glib.Take(unsafe.Pointer(clock)))
-}
-
 // Has returns true if this element has the given flags.
 func (e *Element) Has(flags ElementFlags) bool {
 	return gobool(C.gstObjectFlagIsSet(C.toGstObject(e.unsafe()), C.GstElementFlags(flags)))

gst/gst_pipeline.go

@@ -20,13 +20,7 @@ import (
 // Pipeline is a go implementation of a GstPipeline. Helper methods are provided for constructing
 // pipelines either using file descriptors or the Appsrc/Appsink APIs. The struct itself implements
 // a ReadWriteCloser.
-type Pipeline struct {
-	*Bin
-
-	// a local reference to the bus so duplicates aren't created
-	// when retrieved by the user
-	bus *Bus
-}
+type Pipeline struct{ *Bin }
 
 // NewPipeline allocates and returns a new empty pipeline. If name is empty, one
 // is generated by gstreamer.
@@ -65,15 +59,37 @@ func (p *Pipeline) Instance() *C.GstPipeline { return C.toGstPipeline(p.unsafe()
 
 // GetBus returns the message bus for this pipeline.
 func (p *Pipeline) GetBus() *Bus {
-	if p.bus == nil {
-		cBus := C.gst_pipeline_get_bus((*C.GstPipeline)(p.Instance()))
-		p.bus = wrapBus(glib.Take(unsafe.Pointer(cBus)))
-	}
-	return p.bus
+	cBus := C.gst_pipeline_get_bus((*C.GstPipeline)(p.Instance()))
+	return wrapBus(glib.Take(unsafe.Pointer(cBus)))
 }
 
-// Start will start the GstPipeline. It is asynchronous so it does not need to be
-// called within a goroutine, however, it is still safe to do so.
+// GetPipelineClock returns the global clock for this pipeline.
+func (p *Pipeline) GetPipelineClock() *Clock {
+	cClock := C.gst_pipeline_get_pipeline_clock((*C.GstPipeline)(p.Instance()))
+	return wrapClock(glib.Take(unsafe.Pointer(cClock)))
+}
+
+/*
+SetAutoFlushBus can be used to disable automatically flushing the message bus
+when a pipeline goes to StateNull.
+
+Usually, when a pipeline goes from READY to NULL state, it automatically flushes
+all pending messages on the bus, which is done for refcounting purposes, to break
+circular references.
+
+This means that applications that update state using (async) bus messages (e.g. do
+certain things when a pipeline goes from PAUSED to READY) might not get to see
+messages when the pipeline is shut down, because they might be flushed before they
+can be dispatched in the main thread. This behaviour can be disabled using this function.
+
+It is important that all messages on the bus are handled when the automatic flushing
+is disabled else memory leaks will be introduced.
+*/
+func (p *Pipeline) SetAutoFlushBus(b bool) {
+	C.gst_pipeline_set_auto_flush_bus(p.Instance(), gboolean(b))
+}
+
+// Start is the equivalent to calling SetState(StatePlaying) on the underlying GstElement.
 func (p *Pipeline) Start() error {
 	return p.SetState(StatePlaying)
 }