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927 lines
34 KiB
Markdown
927 lines
34 KiB
Markdown
# Android tutorial 3: Video
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# Goal 
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Except for [Basic tutorial 5: GUI toolkit
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integration](Basic%2Btutorial%2B5%253A%2BGUI%2Btoolkit%2Bintegration.html),
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which embedded a video window on a GTK application, all tutorials so far
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relied on GStreamer video sinks to create a window to display their
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contents. The video sink on Android is not capable of creating its own
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window, so a drawing surface always needs to be provided. This tutorial
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shows:
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- How to allocate a drawing surface on the Android layout and pass it
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to GStreamer
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- How to keep GStreamer posted on changes to the surface
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# Introduction
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Since Android does not provide a windowing system, a GStreamer video
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sink cannot create pop-up windows as it would do on a Desktop platform.
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Fortunately, the `XOverlay` interface allows providing video sinks with
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an already created window onto which they can draw, as we have seen in
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[Basic tutorial 5: GUI toolkit
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integration](Basic%2Btutorial%2B5%253A%2BGUI%2Btoolkit%2Bintegration.html).
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In this tutorial, a
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[SurfaceView](http://developer.android.com/reference/android/view/SurfaceView.html)
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widget (actually, a subclass of it) is placed on the main layout. When
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Android informs the application that a surface has been created for this
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widget, we pass it to the C code which stores it. The
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`check_initialization_complete()` method explained in the previous
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tutorial is extended so that GStreamer is not considered initialized
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until a main loop is running and a drawing surface has been received.
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# A video surface on Android \[Java code\]
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**src/com/gst\_sdk\_tutorials/tutorial\_3/Tutorial3.java**
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``` java
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package com.gst_sdk_tutorials.tutorial_3;
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import android.app.Activity;
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import android.os.Bundle;
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import android.util.Log;
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import android.view.SurfaceHolder;
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import android.view.SurfaceView;
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import android.view.View;
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import android.view.View.OnClickListener;
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import android.widget.ImageButton;
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import android.widget.TextView;
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import android.widget.Toast;
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import com.gstreamer.GStreamer;
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public class Tutorial3 extends Activity implements SurfaceHolder.Callback {
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private native void nativeInit(); // Initialize native code, build pipeline, etc
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private native void nativeFinalize(); // Destroy pipeline and shutdown native code
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private native void nativePlay(); // Set pipeline to PLAYING
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private native void nativePause(); // Set pipeline to PAUSED
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private static native boolean nativeClassInit(); // Initialize native class: cache Method IDs for callbacks
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private native void nativeSurfaceInit(Object surface);
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private native void nativeSurfaceFinalize();
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private long native_custom_data; // Native code will use this to keep private data
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private boolean is_playing_desired; // Whether the user asked to go to PLAYING
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// Called when the activity is first created.
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@Override
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public void onCreate(Bundle savedInstanceState)
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{
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super.onCreate(savedInstanceState);
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// Initialize GStreamer and warn if it fails
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try {
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GStreamer.init(this);
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} catch (Exception e) {
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Toast.makeText(this, e.getMessage(), Toast.LENGTH_LONG).show();
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finish();
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return;
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}
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setContentView(R.layout.main);
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ImageButton play = (ImageButton) this.findViewById(R.id.button_play);
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play.setOnClickListener(new OnClickListener() {
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public void onClick(View v) {
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is_playing_desired = true;
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nativePlay();
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}
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});
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ImageButton pause = (ImageButton) this.findViewById(R.id.button_stop);
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pause.setOnClickListener(new OnClickListener() {
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public void onClick(View v) {
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is_playing_desired = false;
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nativePause();
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}
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});
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SurfaceView sv = (SurfaceView) this.findViewById(R.id.surface_video);
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SurfaceHolder sh = sv.getHolder();
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sh.addCallback(this);
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if (savedInstanceState != null) {
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is_playing_desired = savedInstanceState.getBoolean("playing");
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Log.i ("GStreamer", "Activity created. Saved state is playing:" + is_playing_desired);
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} else {
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is_playing_desired = false;
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Log.i ("GStreamer", "Activity created. There is no saved state, playing: false");
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}
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// Start with disabled buttons, until native code is initialized
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this.findViewById(R.id.button_play).setEnabled(false);
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this.findViewById(R.id.button_stop).setEnabled(false);
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nativeInit();
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}
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protected void onSaveInstanceState (Bundle outState) {
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Log.d ("GStreamer", "Saving state, playing:" + is_playing_desired);
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outState.putBoolean("playing", is_playing_desired);
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}
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protected void onDestroy() {
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nativeFinalize();
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super.onDestroy();
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}
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// Called from native code. This sets the content of the TextView from the UI thread.
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private void setMessage(final String message) {
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final TextView tv = (TextView) this.findViewById(R.id.textview_message);
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runOnUiThread (new Runnable() {
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public void run() {
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tv.setText(message);
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}
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});
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}
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// Called from native code. Native code calls this once it has created its pipeline and
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// the main loop is running, so it is ready to accept commands.
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private void onGStreamerInitialized () {
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Log.i ("GStreamer", "Gst initialized. Restoring state, playing:" + is_playing_desired);
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// Restore previous playing state
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if (is_playing_desired) {
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nativePlay();
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} else {
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nativePause();
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}
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// Re-enable buttons, now that GStreamer is initialized
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final Activity activity = this;
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runOnUiThread(new Runnable() {
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public void run() {
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activity.findViewById(R.id.button_play).setEnabled(true);
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activity.findViewById(R.id.button_stop).setEnabled(true);
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}
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});
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}
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static {
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System.loadLibrary("gstreamer_android");
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System.loadLibrary("tutorial-3");
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nativeClassInit();
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}
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public void surfaceChanged(SurfaceHolder holder, int format, int width,
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int height) {
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Log.d("GStreamer", "Surface changed to format " + format + " width "
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+ width + " height " + height);
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nativeSurfaceInit (holder.getSurface());
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}
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public void surfaceCreated(SurfaceHolder holder) {
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Log.d("GStreamer", "Surface created: " + holder.getSurface());
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}
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public void surfaceDestroyed(SurfaceHolder holder) {
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Log.d("GStreamer", "Surface destroyed");
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nativeSurfaceFinalize ();
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}
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}
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```
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This tutorial continues where the previous one left, adding a video
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surface to the layout and changing the GStreamer pipeline to produce
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video instead of audio. Only the parts of the code that are new will be
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discussed.
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``` java
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private native void nativeSurfaceInit(Object surface);
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private native void nativeSurfaceFinalize();
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```
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Two new entry points to the C code are defined,
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`nativeSurfaceInit()` and `nativeSurfaceFinalize()`, which we will call
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when the video surface becomes available and when it is about to be
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destroyed, respectively.
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``` java
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SurfaceView sv = (SurfaceView) this.findViewById(R.id.surface_video);
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SurfaceHolder sh = sv.getHolder();
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sh.addCallback(this);
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```
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In `onCreate()`, we retrieve the
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[SurfaceView](http://developer.android.com/reference/android/view/SurfaceView.html),
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and then register ourselves to receive notifications about the surface
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state through the
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[SurfaceHolder](http://developer.android.com/reference/android/view/SurfaceHolder.html)
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interface. This is why we declared this Activity as implementing the
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[SurfaceHolder.Callback](http://developer.android.com/reference/android/view/SurfaceHolder.Callback.html)
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interface in line 16.
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``` java
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public void surfaceChanged(SurfaceHolder holder, int format, int width,
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int height) {
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Log.d("GStreamer", "Surface changed to format " + format + " width "
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+ width + " height " + height);
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nativeSurfaceInit (holder.getSurface());
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}
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public void surfaceCreated(SurfaceHolder holder) {
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Log.d("GStreamer", "Surface created: " + holder.getSurface());
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}
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public void surfaceDestroyed(SurfaceHolder holder) {
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Log.d("GStreamer", "Surface destroyed");
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nativeSurfaceFinalize ();
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}
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```
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This interface is composed of the three methods above, which get called
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when the geometry of the surface changes, when the surface is created
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and when it is about to be destroyed. `surfaceChanged()` always gets
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called at least once, right after `surfaceCreated()`, so we will use it
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to notify GStreamer about the new surface. We use
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`surfaceDestroyed()` to tell GStreamer to stop using this surface.
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Let’s review the C code to see what these functions do.
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# A video surface on Android \[C code\]
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**jni/tutorial-3.c**
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``` c
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#include <string.h>
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#include <jni.h>
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#include <android/log.h>
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#include <android/native_window.h>
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#include <android/native_window_jni.h>
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#include <gst/gst.h>
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#include <gst/interfaces/xoverlay.h>
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#include <gst/video/video.h>
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#include <pthread.h>
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GST_DEBUG_CATEGORY_STATIC (debug_category);
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#define GST_CAT_DEFAULT debug_category
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/*
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* These macros provide a way to store the native pointer to CustomData, which might be 32 or 64 bits, into
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* a jlong, which is always 64 bits, without warnings.
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*/
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#if GLIB_SIZEOF_VOID_P == 8
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# define GET_CUSTOM_DATA(env, thiz, fieldID) (CustomData *)(*env)->GetLongField (env, thiz, fieldID)
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# define SET_CUSTOM_DATA(env, thiz, fieldID, data) (*env)->SetLongField (env, thiz, fieldID, (jlong)data)
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#else
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# define GET_CUSTOM_DATA(env, thiz, fieldID) (CustomData *)(jint)(*env)->GetLongField (env, thiz, fieldID)
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# define SET_CUSTOM_DATA(env, thiz, fieldID, data) (*env)->SetLongField (env, thiz, fieldID, (jlong)(jint)data)
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#endif
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/* Structure to contain all our information, so we can pass it to callbacks */
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typedef struct _CustomData {
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jobject app; /* Application instance, used to call its methods. A global reference is kept. */
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GstElement *pipeline; /* The running pipeline */
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GMainContext *context; /* GLib context used to run the main loop */
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GMainLoop *main_loop; /* GLib main loop */
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gboolean initialized; /* To avoid informing the UI multiple times about the initialization */
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GstElement *video_sink; /* The video sink element which receives XOverlay commands */
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ANativeWindow *native_window; /* The Android native window where video will be rendered */
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} CustomData;
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/* These global variables cache values which are not changing during execution */
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static pthread_t gst_app_thread;
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static pthread_key_t current_jni_env;
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static JavaVM *java_vm;
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static jfieldID custom_data_field_id;
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static jmethodID set_message_method_id;
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static jmethodID on_gstreamer_initialized_method_id;
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/*
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* Private methods
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*/
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/* Register this thread with the VM */
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static JNIEnv *attach_current_thread (void) {
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JNIEnv *env;
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JavaVMAttachArgs args;
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GST_DEBUG ("Attaching thread %p", g_thread_self ());
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args.version = JNI_VERSION_1_4;
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args.name = NULL;
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args.group = NULL;
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if ((*java_vm)->AttachCurrentThread (java_vm, &env, &args) < 0) {
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GST_ERROR ("Failed to attach current thread");
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return NULL;
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}
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return env;
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}
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/* Unregister this thread from the VM */
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static void detach_current_thread (void *env) {
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GST_DEBUG ("Detaching thread %p", g_thread_self ());
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(*java_vm)->DetachCurrentThread (java_vm);
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}
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/* Retrieve the JNI environment for this thread */
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static JNIEnv *get_jni_env (void) {
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JNIEnv *env;
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if ((env = pthread_getspecific (current_jni_env)) == NULL) {
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env = attach_current_thread ();
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pthread_setspecific (current_jni_env, env);
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}
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return env;
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}
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/* Change the content of the UI's TextView */
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static void set_ui_message (const gchar *message, CustomData *data) {
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JNIEnv *env = get_jni_env ();
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GST_DEBUG ("Setting message to: %s", message);
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jstring jmessage = (*env)->NewStringUTF(env, message);
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(*env)->CallVoidMethod (env, data->app, set_message_method_id, jmessage);
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if ((*env)->ExceptionCheck (env)) {
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GST_ERROR ("Failed to call Java method");
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(*env)->ExceptionClear (env);
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}
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(*env)->DeleteLocalRef (env, jmessage);
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}
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/* Retrieve errors from the bus and show them on the UI */
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static void error_cb (GstBus *bus, GstMessage *msg, CustomData *data) {
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GError *err;
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gchar *debug_info;
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gchar *message_string;
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gst_message_parse_error (msg, &err, &debug_info);
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message_string = g_strdup_printf ("Error received from element %s: %s", GST_OBJECT_NAME (msg->src), err->message);
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g_clear_error (&err);
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g_free (debug_info);
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set_ui_message (message_string, data);
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g_free (message_string);
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gst_element_set_state (data->pipeline, GST_STATE_NULL);
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}
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/* Notify UI about pipeline state changes */
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static void state_changed_cb (GstBus *bus, GstMessage *msg, CustomData *data) {
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GstState old_state, new_state, pending_state;
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gst_message_parse_state_changed (msg, &old_state, &new_state, &pending_state);
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/* Only pay attention to messages coming from the pipeline, not its children */
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if (GST_MESSAGE_SRC (msg) == GST_OBJECT (data->pipeline)) {
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gchar *message = g_strdup_printf("State changed to %s", gst_element_state_get_name(new_state));
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set_ui_message(message, data);
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g_free (message);
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}
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}
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/* Check if all conditions are met to report GStreamer as initialized.
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* These conditions will change depending on the application */
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static void check_initialization_complete (CustomData *data) {
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JNIEnv *env = get_jni_env ();
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if (!data->initialized && data->native_window && data->main_loop) {
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GST_DEBUG ("Initialization complete, notifying application. native_window:%p main_loop:%p", data->native_window, data->main_loop);
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/* The main loop is running and we received a native window, inform the sink about it */
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gst_x_overlay_set_window_handle (GST_X_OVERLAY (data->video_sink), (guintptr)data->native_window);
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(*env)->CallVoidMethod (env, data->app, on_gstreamer_initialized_method_id);
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if ((*env)->ExceptionCheck (env)) {
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GST_ERROR ("Failed to call Java method");
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(*env)->ExceptionClear (env);
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}
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data->initialized = TRUE;
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}
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}
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/* Main method for the native code. This is executed on its own thread. */
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static void *app_function (void *userdata) {
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JavaVMAttachArgs args;
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GstBus *bus;
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CustomData *data = (CustomData *)userdata;
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GSource *bus_source;
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GError *error = NULL;
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GST_DEBUG ("Creating pipeline in CustomData at %p", data);
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/* Create our own GLib Main Context and make it the default one */
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data->context = g_main_context_new ();
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g_main_context_push_thread_default(data->context);
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/* Build pipeline */
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data->pipeline = gst_parse_launch("videotestsrc ! warptv ! ffmpegcolorspace ! autovideosink", &error);
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if (error) {
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gchar *message = g_strdup_printf("Unable to build pipeline: %s", error->message);
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g_clear_error (&error);
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set_ui_message(message, data);
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g_free (message);
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return NULL;
|
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}
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|
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/* Set the pipeline to READY, so it can already accept a window handle, if we have one */
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gst_element_set_state(data->pipeline, GST_STATE_READY);
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|
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data->video_sink = gst_bin_get_by_interface(GST_BIN(data->pipeline), GST_TYPE_X_OVERLAY);
|
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if (!data->video_sink) {
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GST_ERROR ("Could not retrieve video sink");
|
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return NULL;
|
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}
|
||
|
||
/* Instruct the bus to emit signals for each received message, and connect to the interesting signals */
|
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bus = gst_element_get_bus (data->pipeline);
|
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bus_source = gst_bus_create_watch (bus);
|
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g_source_set_callback (bus_source, (GSourceFunc) gst_bus_async_signal_func, NULL, NULL);
|
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g_source_attach (bus_source, data->context);
|
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g_source_unref (bus_source);
|
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g_signal_connect (G_OBJECT (bus), "message::error", (GCallback)error_cb, data);
|
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g_signal_connect (G_OBJECT (bus), "message::state-changed", (GCallback)state_changed_cb, data);
|
||
gst_object_unref (bus);
|
||
|
||
/* Create a GLib Main Loop and set it to run */
|
||
GST_DEBUG ("Entering main loop... (CustomData:%p)", data);
|
||
data->main_loop = g_main_loop_new (data->context, FALSE);
|
||
check_initialization_complete (data);
|
||
g_main_loop_run (data->main_loop);
|
||
GST_DEBUG ("Exited main loop");
|
||
g_main_loop_unref (data->main_loop);
|
||
data->main_loop = NULL;
|
||
|
||
/* Free resources */
|
||
g_main_context_pop_thread_default(data->context);
|
||
g_main_context_unref (data->context);
|
||
gst_element_set_state (data->pipeline, GST_STATE_NULL);
|
||
gst_object_unref (data->video_sink);
|
||
gst_object_unref (data->pipeline);
|
||
|
||
return NULL;
|
||
}
|
||
|
||
/*
|
||
* Java Bindings
|
||
*/
|
||
|
||
/* Instruct the native code to create its internal data structure, pipeline and thread */
|
||
static void gst_native_init (JNIEnv* env, jobject thiz) {
|
||
CustomData *data = g_new0 (CustomData, 1);
|
||
SET_CUSTOM_DATA (env, thiz, custom_data_field_id, data);
|
||
GST_DEBUG_CATEGORY_INIT (debug_category, "tutorial-3", 0, "Android tutorial 3");
|
||
gst_debug_set_threshold_for_name("tutorial-3", GST_LEVEL_DEBUG);
|
||
GST_DEBUG ("Created CustomData at %p", data);
|
||
data->app = (*env)->NewGlobalRef (env, thiz);
|
||
GST_DEBUG ("Created GlobalRef for app object at %p", data->app);
|
||
pthread_create (&gst_app_thread, NULL, &app_function, data);
|
||
}
|
||
|
||
/* Quit the main loop, remove the native thread and free resources */
|
||
static void gst_native_finalize (JNIEnv* env, jobject thiz) {
|
||
CustomData *data = GET_CUSTOM_DATA (env, thiz, custom_data_field_id);
|
||
if (!data) return;
|
||
GST_DEBUG ("Quitting main loop...");
|
||
g_main_loop_quit (data->main_loop);
|
||
GST_DEBUG ("Waiting for thread to finish...");
|
||
pthread_join (gst_app_thread, NULL);
|
||
GST_DEBUG ("Deleting GlobalRef for app object at %p", data->app);
|
||
(*env)->DeleteGlobalRef (env, data->app);
|
||
GST_DEBUG ("Freeing CustomData at %p", data);
|
||
g_free (data);
|
||
SET_CUSTOM_DATA (env, thiz, custom_data_field_id, NULL);
|
||
GST_DEBUG ("Done finalizing");
|
||
}
|
||
|
||
/* Set pipeline to PLAYING state */
|
||
static void gst_native_play (JNIEnv* env, jobject thiz) {
|
||
CustomData *data = GET_CUSTOM_DATA (env, thiz, custom_data_field_id);
|
||
if (!data) return;
|
||
GST_DEBUG ("Setting state to PLAYING");
|
||
gst_element_set_state (data->pipeline, GST_STATE_PLAYING);
|
||
}
|
||
|
||
/* Set pipeline to PAUSED state */
|
||
static void gst_native_pause (JNIEnv* env, jobject thiz) {
|
||
CustomData *data = GET_CUSTOM_DATA (env, thiz, custom_data_field_id);
|
||
if (!data) return;
|
||
GST_DEBUG ("Setting state to PAUSED");
|
||
gst_element_set_state (data->pipeline, GST_STATE_PAUSED);
|
||
}
|
||
|
||
/* Static class initializer: retrieve method and field IDs */
|
||
static jboolean gst_native_class_init (JNIEnv* env, jclass klass) {
|
||
custom_data_field_id = (*env)->GetFieldID (env, klass, "native_custom_data", "J");
|
||
set_message_method_id = (*env)->GetMethodID (env, klass, "setMessage", "(Ljava/lang/String;)V");
|
||
on_gstreamer_initialized_method_id = (*env)->GetMethodID (env, klass, "onGStreamerInitialized", "()V");
|
||
|
||
if (!custom_data_field_id || !set_message_method_id || !on_gstreamer_initialized_method_id) {
|
||
/* We emit this message through the Android log instead of the GStreamer log because the later
|
||
* has not been initialized yet.
|
||
*/
|
||
__android_log_print (ANDROID_LOG_ERROR, "tutorial-3", "The calling class does not implement all necessary interface methods");
|
||
return JNI_FALSE;
|
||
}
|
||
return JNI_TRUE;
|
||
}
|
||
|
||
static void gst_native_surface_init (JNIEnv *env, jobject thiz, jobject surface) {
|
||
CustomData *data = GET_CUSTOM_DATA (env, thiz, custom_data_field_id);
|
||
if (!data) return;
|
||
ANativeWindow *new_native_window = ANativeWindow_fromSurface(env, surface);
|
||
GST_DEBUG ("Received surface %p (native window %p)", surface, new_native_window);
|
||
|
||
if (data->native_window) {
|
||
ANativeWindow_release (data->native_window);
|
||
if (data->native_window == new_native_window) {
|
||
GST_DEBUG ("New native window is the same as the previous one", data->native_window);
|
||
if (data->video_sink) {
|
||
gst_x_overlay_expose(GST_X_OVERLAY (data->video_sink));
|
||
gst_x_overlay_expose(GST_X_OVERLAY (data->video_sink));
|
||
}
|
||
return;
|
||
} else {
|
||
GST_DEBUG ("Released previous native window %p", data->native_window);
|
||
data->initialized = FALSE;
|
||
}
|
||
}
|
||
data->native_window = new_native_window;
|
||
|
||
check_initialization_complete (data);
|
||
}
|
||
|
||
static void gst_native_surface_finalize (JNIEnv *env, jobject thiz) {
|
||
CustomData *data = GET_CUSTOM_DATA (env, thiz, custom_data_field_id);
|
||
if (!data) return;
|
||
GST_DEBUG ("Releasing Native Window %p", data->native_window);
|
||
|
||
if (data->video_sink) {
|
||
gst_x_overlay_set_window_handle (GST_X_OVERLAY (data->video_sink), (guintptr)NULL);
|
||
gst_element_set_state (data->pipeline, GST_STATE_READY);
|
||
}
|
||
|
||
ANativeWindow_release (data->native_window);
|
||
data->native_window = NULL;
|
||
data->initialized = FALSE;
|
||
}
|
||
|
||
/* List of implemented native methods */
|
||
static JNINativeMethod native_methods[] = {
|
||
{ "nativeInit", "()V", (void *) gst_native_init},
|
||
{ "nativeFinalize", "()V", (void *) gst_native_finalize},
|
||
{ "nativePlay", "()V", (void *) gst_native_play},
|
||
{ "nativePause", "()V", (void *) gst_native_pause},
|
||
{ "nativeSurfaceInit", "(Ljava/lang/Object;)V", (void *) gst_native_surface_init},
|
||
{ "nativeSurfaceFinalize", "()V", (void *) gst_native_surface_finalize},
|
||
{ "nativeClassInit", "()Z", (void *) gst_native_class_init}
|
||
};
|
||
|
||
/* Library initializer */
|
||
jint JNI_OnLoad(JavaVM *vm, void *reserved) {
|
||
JNIEnv *env = NULL;
|
||
|
||
java_vm = vm;
|
||
|
||
if ((*vm)->GetEnv(vm, (void**) &env, JNI_VERSION_1_4) != JNI_OK) {
|
||
__android_log_print (ANDROID_LOG_ERROR, "tutorial-3", "Could not retrieve JNIEnv");
|
||
return 0;
|
||
}
|
||
jclass klass = (*env)->FindClass (env, "com/gst_sdk_tutorials/tutorial_3/Tutorial3");
|
||
(*env)->RegisterNatives (env, klass, native_methods, G_N_ELEMENTS(native_methods));
|
||
|
||
pthread_key_create (¤t_jni_env, detach_current_thread);
|
||
|
||
return JNI_VERSION_1_4;
|
||
}
|
||
```
|
||
|
||
First, our `CustomData` structure is augmented to keep a pointer to the
|
||
video sink element and the native window
|
||
handle:
|
||
|
||
``` c
|
||
GstElement *video_sink; /* The video sink element which receives XOverlay commands */
|
||
ANativeWindow *native_window; /* The Android native window where video will be rendered */
|
||
```
|
||
|
||
The `check_initialization_complete()` method is also augmented so that
|
||
it requires a native window before considering GStreamer to be
|
||
initialized:
|
||
|
||
``` c
|
||
static void check_initialization_complete (CustomData *data) {
|
||
JNIEnv *env = get_jni_env ();
|
||
if (!data->initialized && data->native_window && data->main_loop) {
|
||
GST_DEBUG ("Initialization complete, notifying application. native_window:%p main_loop:%p", data->native_window, data->main_loop);
|
||
|
||
/* The main loop is running and we received a native window, inform the sink about it */
|
||
gst_x_overlay_set_window_handle (GST_X_OVERLAY (data->video_sink), (guintptr)data->native_window);
|
||
|
||
(*env)->CallVoidMethod (env, data->app, on_gstreamer_initialized_method_id);
|
||
if ((*env)->ExceptionCheck (env)) {
|
||
GST_ERROR ("Failed to call Java method");
|
||
(*env)->ExceptionClear (env);
|
||
}
|
||
data->initialized = TRUE;
|
||
}
|
||
}
|
||
```
|
||
|
||
Also, once the pipeline has been built and a native window has been
|
||
received, we inform the video sink of the window handle to use via the
|
||
`gst_x_overlay_set_window_handle()` method.
|
||
|
||
The GStreamer pipeline for this tutorial involves a `videotestsrc`, a
|
||
`warptv` psychedelic distorter effect (check out other cool video
|
||
effects in the `GSTREAMER_PLUGINS_EFFECTS` package), and an
|
||
`autovideosink` which will instantiate the adequate video sink for the
|
||
platform:
|
||
|
||
``` c
|
||
data->pipeline = gst_parse_launch("videotestsrc ! warptv ! ffmpegcolorspace ! autovideosink ", &error);
|
||
```
|
||
|
||
Here things start to get more
|
||
interesting:
|
||
|
||
``` c
|
||
/* Set the pipeline to READY, so it can already accept a window handle, if we have one */
|
||
gst_element_set_state(data->pipeline, GST_STATE_READY);
|
||
|
||
data->video_sink = gst_bin_get_by_interface(GST_BIN(data->pipeline), GST_TYPE_X_OVERLAY);
|
||
if (!data->video_sink) {
|
||
GST_ERROR ("Could not retrieve video sink");
|
||
return NULL;
|
||
}
|
||
```
|
||
|
||
We start by setting the pipeline to the READY state. No data flow occurs
|
||
yet, but the `autovideosink` will instantiate the actual sink so we can
|
||
ask for it immediately.
|
||
|
||
The `gst_bin_get_by_interface()` method will examine the whole pipeline
|
||
and return a pointer to an element which supports the requested
|
||
interface. We are asking for the `XOverlay` interface, explained in
|
||
[Basic tutorial 5: GUI toolkit
|
||
integration](Basic%2Btutorial%2B5%253A%2BGUI%2Btoolkit%2Bintegration.html),
|
||
which controls how to perform rendering into foreign (non-GStreamer)
|
||
windows. The internal video sink instantiated by `autovideosink` is the
|
||
only element in this pipeline implementing it, so it will be returned.
|
||
|
||
Now we will implement the two native functions called by the Java code
|
||
when the drawing surface becomes available or is about to be
|
||
destroyed:
|
||
|
||
``` c
|
||
static void gst_native_surface_init (JNIEnv *env, jobject thiz, jobject surface) {
|
||
CustomData *data = GET_CUSTOM_DATA (env, thiz, custom_data_field_id);
|
||
if (!data) return;
|
||
ANativeWindow *new_native_window = ANativeWindow_fromSurface(env, surface);
|
||
GST_DEBUG ("Received surface %p (native window %p)", surface, new_native_window);
|
||
|
||
if (data->native_window) {
|
||
ANativeWindow_release (data->native_window);
|
||
if (data->native_window == new_native_window) {
|
||
GST_DEBUG ("New native window is the same as the previous one", data->native_window);
|
||
if (data->video_sink) {
|
||
gst_x_overlay_expose(GST_X_OVERLAY (data->video_sink));
|
||
gst_x_overlay_expose(GST_X_OVERLAY (data->video_sink));
|
||
}
|
||
return;
|
||
} else {
|
||
GST_DEBUG ("Released previous native window %p", data->native_window);
|
||
data->initialized = FALSE;
|
||
}
|
||
}
|
||
data->native_window = new_native_window;
|
||
|
||
check_initialization_complete (data);
|
||
}
|
||
```
|
||
|
||
This method is responsible for providing the video sink with the window
|
||
handle coming from the Java code. We are passed a
|
||
[Surface](http://developer.android.com/reference/android/view/Surface.html)
|
||
object, and we use `ANativeWindow_fromSurface()` to obtain the
|
||
underlying native window pointer. There is no official online
|
||
documentation for the NDK, but fortunately the header files are well
|
||
commented. Native window management functions can be found in
|
||
`$(ANDROID_NDK_ROOT)\platforms\android-9\arch-arm\usr\include\android\native_window.h` and `native_window_jni.h`
|
||
|
||
If we had already stored a native window, the one we just received can
|
||
either be a new one, or just an update of the one we have. If the
|
||
pointers are the same, we assume the geometry of the surface has
|
||
changed, and simply instruct the video sink to redraw itself, via the
|
||
`gst_x_overlay_expose()` method. The video sink will recover the new
|
||
size from the surface itself, so we do not need to bother about it
|
||
here. We need to call `gst_x_overlay_expose()` twice because of the way
|
||
the surface changes propagate down the OpenGL ES / EGL pipeline (The
|
||
only video sink available for Android in the GStreamer SDK uses OpenGL
|
||
ES). By the time we call the first expose, the surface that the sink
|
||
will pick up still contains the old size.
|
||
|
||
On the other hand, if the pointers are different, we mark GStreamer as
|
||
not being initialized. Next time we call
|
||
`check_initialization_complete()`, the video sink will be informed of
|
||
the new window handle.
|
||
|
||
We finally store the new window handle and call
|
||
`check_initialization_complete()` to inform the Java code that
|
||
everything is set up, if that is the case.
|
||
|
||
``` c
|
||
static void gst_native_surface_finalize (JNIEnv *env, jobject thiz) {
|
||
CustomData *data = GET_CUSTOM_DATA (env, thiz, custom_data_field_id);
|
||
if (!data) return;
|
||
GST_DEBUG ("Releasing Native Window %p", data->native_window);
|
||
|
||
if (data->video_sink) {
|
||
gst_x_overlay_set_window_handle (GST_X_OVERLAY (data->video_sink), (guintptr)NULL);
|
||
gst_element_set_state (data->pipeline, GST_STATE_READY);
|
||
}
|
||
|
||
ANativeWindow_release (data->native_window);
|
||
data->native_window = NULL;
|
||
data->initialized = FALSE;
|
||
}
|
||
```
|
||
|
||
The complementary function, `gst_native_surface_finalize()` is called
|
||
when a surface is about to be destroyed and should not be used anymore.
|
||
Here, we simply instruct the video sink to stop using the window handle
|
||
and set the pipeline to READY so no rendering occurs. We release the
|
||
window pointer we had stored with `ANativeWindow_release()`, and mark
|
||
GStreamer as not being initialized anymore.
|
||
|
||
And this is all there is to it, regarding the main code. Only a couple
|
||
of details remain, the subclass we made for SurfaceView and the
|
||
`Android.mk` file.
|
||
|
||
# GStreamerSurfaceView, a convenient SurfaceView wrapper \[Java code\]
|
||
|
||
By default,
|
||
[SurfaceView](http://developer.android.com/reference/android/view/SurfaceView.html) does
|
||
not have any particular size, so it expands to use all the space the
|
||
layout can give it. While this might be convenient sometimes, it does
|
||
not allow a great deal of control. In particular, when the surface does
|
||
not have the same aspect ratio as the media, the sink will add black
|
||
borders (the known “letterbox” or “pillarbox” effect), which is an
|
||
unnecessary work (and a waste of battery).
|
||
|
||
The subclass of
|
||
[SurfaceView](http://developer.android.com/reference/android/view/SurfaceView.html) presented
|
||
here overrides the
|
||
[onMeasure()](http://developer.android.com/reference/android/view/SurfaceView.html#onMeasure\(int,%20int\)) method
|
||
to report the actual media size, so the surface can adapt to any layout
|
||
while preserving the media aspect ratio.
|
||
|
||
Since in this tutorial the media size is known beforehand, it is
|
||
hardcoded in the GStreamerSurfaceView class for simplicity. The next
|
||
tutorial shows how it can be recovered at runtime and passed onto the
|
||
surface.
|
||
|
||
**src/com/gst\_sdk\_tutorials/tutorial\_3/GStreamerSurfaceView.java**
|
||
|
||
``` java
|
||
package com.gst_sdk_tutorials.tutorial_3;
|
||
|
||
import android.content.Context;
|
||
import android.util.AttributeSet;
|
||
import android.util.Log;
|
||
import android.view.SurfaceView;
|
||
import android.view.View;
|
||
|
||
// A simple SurfaceView whose width and height can be set from the outside
|
||
public class GStreamerSurfaceView extends SurfaceView {
|
||
public int media_width = 320;
|
||
public int media_height = 240;
|
||
|
||
// Mandatory constructors, they do not do much
|
||
public GStreamerSurfaceView(Context context, AttributeSet attrs,
|
||
int defStyle) {
|
||
super(context, attrs, defStyle);
|
||
}
|
||
|
||
public GStreamerSurfaceView(Context context, AttributeSet attrs) {
|
||
super(context, attrs);
|
||
}
|
||
|
||
public GStreamerSurfaceView (Context context) {
|
||
super(context);
|
||
}
|
||
|
||
// Called by the layout manager to find out our size and give us some rules.
|
||
// We will try to maximize our size, and preserve the media's aspect ratio if
|
||
// we are given the freedom to do so.
|
||
@Override
|
||
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
|
||
int width = 0, height = 0;
|
||
int wmode = View.MeasureSpec.getMode(widthMeasureSpec);
|
||
int hmode = View.MeasureSpec.getMode(heightMeasureSpec);
|
||
int wsize = View.MeasureSpec.getSize(widthMeasureSpec);
|
||
int hsize = View.MeasureSpec.getSize(heightMeasureSpec);
|
||
|
||
Log.i ("GStreamer", "onMeasure called with " + media_width + "x" + media_height);
|
||
// Obey width rules
|
||
switch (wmode) {
|
||
case View.MeasureSpec.AT_MOST:
|
||
if (hmode == View.MeasureSpec.EXACTLY) {
|
||
width = Math.min(hsize * media_width / media_height, wsize);
|
||
break;
|
||
}
|
||
case View.MeasureSpec.EXACTLY:
|
||
width = wsize;
|
||
break;
|
||
case View.MeasureSpec.UNSPECIFIED:
|
||
width = media_width;
|
||
}
|
||
|
||
// Obey height rules
|
||
switch (hmode) {
|
||
case View.MeasureSpec.AT_MOST:
|
||
if (wmode == View.MeasureSpec.EXACTLY) {
|
||
height = Math.min(wsize * media_height / media_width, hsize);
|
||
break;
|
||
}
|
||
case View.MeasureSpec.EXACTLY:
|
||
height = hsize;
|
||
break;
|
||
case View.MeasureSpec.UNSPECIFIED:
|
||
height = media_height;
|
||
}
|
||
|
||
// Finally, calculate best size when both axis are free
|
||
if (hmode == View.MeasureSpec.AT_MOST && wmode == View.MeasureSpec.AT_MOST) {
|
||
int correct_height = width * media_height / media_width;
|
||
int correct_width = height * media_width / media_height;
|
||
|
||
if (correct_height < height)
|
||
height = correct_height;
|
||
else
|
||
width = correct_width;
|
||
}
|
||
|
||
// Obey minimum size
|
||
width = Math.max (getSuggestedMinimumWidth(), width);
|
||
height = Math.max (getSuggestedMinimumHeight(), height);
|
||
setMeasuredDimension(width, height);
|
||
}
|
||
|
||
}
|
||
```
|
||
|
||
# A video surface on Android \[Android.mk\]
|
||
|
||
**/jni/Android.mk**
|
||
|
||
``` ruby
|
||
LOCAL_PATH := $(call my-dir)
|
||
|
||
include $(CLEAR_VARS)
|
||
|
||
LOCAL_MODULE := tutorial-3
|
||
LOCAL_SRC_FILES := tutorial-3.c
|
||
LOCAL_SHARED_LIBRARIES := gstreamer_android
|
||
LOCAL_LDLIBS := -llog -landroid
|
||
include $(BUILD_SHARED_LIBRARY)
|
||
|
||
ifndef GSTREAMER_SDK_ROOT
|
||
ifndef GSTREAMER_SDK_ROOT_ANDROID
|
||
$(error GSTREAMER_SDK_ROOT_ANDROID is not defined!)
|
||
endif
|
||
GSTREAMER_SDK_ROOT := $(GSTREAMER_SDK_ROOT_ANDROID)
|
||
endif
|
||
GSTREAMER_NDK_BUILD_PATH := $(GSTREAMER_SDK_ROOT)/share/gst-android/ndk-build/
|
||
include $(GSTREAMER_NDK_BUILD_PATH)/plugins.mk
|
||
GSTREAMER_PLUGINS := $(GSTREAMER_PLUGINS_CORE) $(GSTREAMER_PLUGINS_SYS) $(GSTREAMER_PLUGINS_EFFECTS)
|
||
GSTREAMER_EXTRA_DEPS := gstreamer-interfaces-1.0 gstreamer-video-1.0
|
||
include $(GSTREAMER_NDK_BUILD_PATH)/gstreamer.mk
|
||
```
|
||
|
||
Worth mentioning is the `-landroid` library being used to allow
|
||
interaction with the native windows, and the different plugin
|
||
packages: `GSTREAMER_PLUGINS_SYS` for the system-dependent video sink
|
||
and `GSTREAMER_PLUGINS_EFFECTS` for the `warptv` element. This tutorial
|
||
requires the `gstreamer-interfaces` library to use the
|
||
`XOverlay` interface, and the `gstreamer-video` library to use the
|
||
video helper methods.
|
||
|
||
# Conclusion
|
||
|
||
This tutorial has shown:
|
||
|
||
- How to display video on Android using a
|
||
[SurfaceView](http://developer.android.com/reference/android/view/SurfaceView.html) and
|
||
the `XOverlay` interface.
|
||
- How to be aware of changes in the surface’s size using
|
||
[SurfaceView](http://developer.android.com/reference/android/view/SurfaceView.html)’s
|
||
callbacks.
|
||
- How to report the media size to the Android layout engine.
|
||
|
||
The following tutorial plays an actual clip and adds a few more controls
|
||
to this tutorial in order to build a simple media player.
|
||
|
||
It has been a pleasure having you here, and see you soon\!
|
||
|
||
## Attachments:
|
||
|
||
|
||
[tutorial3-screenshot.png](attachments/2687065/2654414.png)
|
||
(image/png)
|
||
|
||
[tutorial3-screenshot.png](attachments/2687065/2654415.png)
|
||
(image/png)
|
||
|
||
[tutorial3-screenshot.png](attachments/2687065/2654418.png)
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[tutorial3-screenshot.png](attachments/2687065/2654413.png)
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