decodebin example and fix up signal handling

examples/decodebin/main.go

@@ -0,0 +1,170 @@
+package main
+
+import (
+	"errors"
+	"flag"
+	"fmt"
+	"os"
+	"strings"
+	"time"
+
+	"github.com/tinyzimmer/go-gst/examples"
+	"github.com/tinyzimmer/go-gst/gst"
+)
+
+var srcFile string
+
+func buildPipeline() (*gst.Pipeline, error) {
+	gst.Init(nil)
+
+	pipeline, err := gst.NewPipeline("")
+	if err != nil {
+		return nil, err
+	}
+
+	src, err := gst.NewElement("filesrc")
+	if err != nil {
+		return nil, err
+	}
+
+	decodebin, err := gst.NewElement("decodebin")
+	if err != nil {
+		return nil, err
+	}
+
+	src.Set("location", srcFile)
+
+	pipeline.AddMany(src, decodebin)
+	src.Link(decodebin)
+
+	// Connect to decodebin's pad-added signal, that is emitted whenever
+	// it found another stream from the input file and found a way to decode it to its raw format.
+	// decodebin automatically adds a src-pad for this raw stream, which
+	// we can use to build the follow-up pipeline.
+	decodebin.Connect("pad-added", func(self *gst.Element, srcPad *gst.Pad) {
+
+		// Try to detect whether this is video or audio
+		var isAudio, isVideo bool
+		caps := srcPad.GetCurrentCaps()
+		for i := 0; i < caps.GetSize(); i++ {
+			st := caps.GetStructureAt(i)
+			if strings.HasPrefix(st.Name(), "audio/") {
+				isAudio = true
+			}
+			if strings.HasPrefix(st.Name(), "video/") {
+				isVideo = true
+			}
+		}
+
+		fmt.Printf("New pad added, is_audio=%v, is_video=%v\n", isAudio, isVideo)
+
+		if !isAudio && !isVideo {
+			err := errors.New("Could not detect media stream type")
+			// We can send errors directly to the pipeline bus if they occur.
+			// These will be handled downstream.
+			msg := gst.NewErrorMessage(self, gst.NewGError(1, err), fmt.Sprintf("Received caps: %s", caps.String()), nil)
+			pipeline.GetPipelineBus().Post(msg)
+			return
+		}
+
+		if isAudio {
+			// decodebin found a raw audiostream, so we build the follow-up pipeline to
+			// play it on the default audio playback device (using autoaudiosink).
+			elements, err := gst.NewElementMany("queue", "audioconvert", "audioresample", "autoaudiosink")
+			if err != nil {
+				msg := gst.NewErrorMessage(self, gst.NewGError(2, err), "", nil)
+				pipeline.GetPipelineBus().Post(msg)
+				fmt.Println("ERROR: Could not create elements for audio pipeline")
+				return
+			}
+			pipeline.AddMany(elements...)
+			gst.ElementLinkMany(elements...)
+
+			// !!ATTENTION!!:
+			// This is quite important and people forget it often. Without making sure that
+			// the new elements have the same state as the pipeline, things will fail later.
+			// They would still be in Null state and can't process data.
+			for _, e := range elements {
+				e.SyncStateWithParent()
+			}
+
+			// The queue was the first element returned above
+			queue := elements[0]
+			// Get the queue element's sink pad and link the decodebin's newly created
+			// src pad for the audio stream to it.
+			sinkPad := queue.GetStaticPad("sink")
+			srcPad.Link(sinkPad)
+
+		} else if isVideo {
+			// decodebin found a raw videostream, so we build the follow-up pipeline to
+			// display it using the autovideosink.
+			elements, err := gst.NewElementMany("queue", "videoconvert", "videoscale", "autovideosink")
+			if err != nil {
+				msg := gst.NewErrorMessage(self, gst.NewGError(2, err), "", nil)
+				pipeline.GetPipelineBus().Post(msg)
+				fmt.Println("ERROR: Could not create elements for audio pipeline")
+				return
+			}
+			pipeline.AddMany(elements...)
+			gst.ElementLinkMany(elements...)
+
+			for _, e := range elements {
+				e.SyncStateWithParent()
+			}
+
+			queue := elements[0]
+			// Get the queue element's sink pad and link the decodebin's newly created
+			// src pad for the video stream to it.
+			sinkPad := queue.GetStaticPad("sink")
+			srcPad.Link(sinkPad)
+		}
+	})
+	return pipeline, nil
+}
+
+func handleMessage(msg *gst.Message) error {
+	defer msg.Unref() // Messages are a good candidate for trying out runtime finalizers
+
+	switch msg.Type() {
+	case gst.MessageEOS:
+		return errors.New("end-of-stream")
+	case gst.MessageError:
+		return msg.ParseError()
+	}
+
+	return nil
+}
+
+func runPipeline(pipeline *gst.Pipeline) error {
+	pipeline.SetState(gst.StatePlaying)
+
+	bus := pipeline.GetPipelineBus()
+
+	for {
+		msg := bus.TimedPop(time.Duration(-1))
+		if msg == nil {
+			break
+		}
+		if err := handleMessage(msg); err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
+func main() {
+	flag.StringVar(&srcFile, "f", "", "The file to decode")
+	flag.Parse()
+	if srcFile == "" {
+		flag.Usage()
+		os.Exit(1)
+	}
+	examples.RunLoop(func(loop *gst.MainLoop) error {
+		pipeline, err := buildPipeline()
+		if err != nil {
+			return err
+		}
+		return runPipeline(pipeline)
+	})
+}