go-gst/examples/toc/main.go

// This example demonstrates the use of GStreamer's ToC API.
//
// This API is used to manage a table of contents contained in the handled media stream.
// Chapters within a matroska file would be an example of a scenario for using
// this API. Elements that can parse ToCs from a stream (such as matroskademux)
// notify all elements in the pipeline when they encountered a ToC.
// For this, the example operates the following pipeline:
//
//	                         /-{queue} - {fakesink}
//	{filesrc} - {decodebin} - {queue} - {fakesink}
//	                         \- ...
package main

import (
	"errors"
	"fmt"
	"os"
	"time"

	"github.com/go-gst/go-glib/glib"
	"github.com/go-gst/go-gst/examples"
	"github.com/go-gst/go-gst/gst"
)

func tagsetter(mainLoop *glib.MainLoop) error {
	gst.Init(nil)

	if len(os.Args) < 2 {
		return errors.New("Usage: toc <file>")
	}

	pipeline, err := gst.NewPipeline("")
	if err != nil {
		return err
	}

	src, err := gst.NewElement("filesrc")
	if err != nil {
		return err
	}
	decodebin, err := gst.NewElement("decodebin")
	if err != nil {
		return err
	}

	src.SetProperty("location", os.Args[1])

	pipeline.AddMany(src, decodebin)
	gst.ElementLinkMany(src, 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.Connect("pad-added", func(_ *gst.Element, srcPad *gst.Pad) {

		// In this example, we are only interested about parsing the ToC, so
		// we simply pipe every encountered stream into a fakesink, essentially
		// throwing away the data.
		elems, err := gst.NewElementMany("queue", "fakesink")
		if err != nil {
			fmt.Println("Could not create decodebin pipeline")
			return
		}
		pipeline.AddMany(elems...)
		gst.ElementLinkMany(elems...)
		for _, e := range elems {
			e.SyncStateWithParent()
		}

		queue := elems[0]
		sinkPad := queue.GetStaticPad("sink")
		if sinkPad == nil {
			fmt.Println("Could not get static pad from sink")
			return
		}

		srcPad.
			Link(sinkPad)
	})

	if err := pipeline.SetState(gst.StatePaused); err != nil {
		return err
	}

	// Instead of using the main loop, we manually iterate over GStreamer's bus messages
	// in this example. We don't need any special functionality like timeouts or GLib socket
	// notifications, so this is sufficient. The bus is manually operated by repeatedly calling
	// timed_pop on the bus with the desired timeout for when to stop waiting for new messages.
	// (-1 = Wait forever)
	for {
		msg := pipeline.GetPipelineBus().TimedPop(time.Duration(-1))
		switch msg.Type() {

		// When we use this method of popping from the bus (instead of a Watch), we own a
		// reference to every message received (this may be abstracted later).
		default:
			// fmt.Println(msg)
			msg.Unref()

		// End of stream
		case gst.MessageEOS:
			msg.Unref()
			break

			// Errors from any elements
		case gst.MessageError:
			gerr := msg.ParseError()
			if debug := gerr.DebugString(); debug != "" {
				fmt.Println("go-gst-debug:", debug)
			}
			msg.Unref()
			return gerr

		// Some element found a ToC in the current media stream and told
		// us by posting a message to GStreamer's bus.
		case gst.MessageTOC:
			// Parse the toc from the message
			toc, updated := msg.ParseTOC()
			msg.Unref()
			fmt.Printf("Received toc: %s - updated %v\n", toc.GetScope(), updated)
			// Get a list of tags that are ToC specific.
			if tags := toc.GetTags(); tags != nil {
				fmt.Println("- tags:", tags)
			}
			// ToCs do not have a fixed structure. Depending on the format that
			// they were parsed from, they might have different tree-like structures,
			// so applications that want to support ToCs (for example in the form
			// of jumping between chapters in a video) have to try parsing  and
			// interpreting the ToC manually.
			// In this example, we simply want to print the ToC structure, so
			// we iterate everything and don't try to interpret anything.
			for _, entry := range toc.GetEntries() {
				// Every entry in a ToC has its own type. One type could for
				// example be Chapter.
				fmt.Printf("\t%s - %s\n", entry.GetEntryTypeString(), entry.GetUID())

				// Every ToC entry can have a set of timestamps (start, stop).
				if ok, start, stop := entry.GetStartStopTimes(); ok {
					startDur := time.Duration(start) * time.Nanosecond
					stopDur := time.Duration(stop) * time.Nanosecond
					fmt.Printf("\t- start: %s, stop: %s\n", startDur, stopDur)
				}

				// Every ToC entry can have tags to it.
				if tags := entry.GetTags(); tags != nil {
					fmt.Println("\t- tags:", tags)
				}

				// Every ToC entry can have a set of child entries.
				// With this structure, you can create trees of arbitrary depth.
				for _, subEntry := range entry.GetSubEntries() {
					fmt.Printf("\n\t\t%s - %s\n", subEntry.GetEntryTypeString(), subEntry.GetUID())
					if ok, start, stop := entry.GetStartStopTimes(); ok {
						startDur := time.Duration(start) * time.Nanosecond
						stopDur := time.Duration(stop) * time.Nanosecond
						fmt.Printf("\t\t- start: %s, stop: %s\n", startDur, stopDur)
					}
					if tags := entry.GetTags(); tags != nil {
						fmt.Println("\t\t- tags:", tags)
					}
				}
			}

			toc.Unref()
		}
	}
}

func main() {
	examples.RunLoop(tagsetter)
}