Updates VideoDecoder plugin API to GDExtension.

Adds VideoStream and relevant resource loaders to migrate
external GDNative plugins to GDExtension.

Adds a VideoStreamLoader as a specialization of ResourceFormatLoader
as ClassDB::is_parent_class is inaccessible from GDExtension currently.

Using Object* instead of Ref<T> in order to avoid the refcount bug
(godotengine/godot-cpp#652)
Also another bug is in ResourceLoader in use on the extension side that
requires fixing.

10 files changed, 383 insertions, 81 deletions

diff --git a/doc/classes/VideoStream.xml b/doc/classes/VideoStream.xml
index 2797ad3513..648c3edd73 100644
--- a/doc/classes/VideoStream.xml
+++ b/doc/classes/VideoStream.xml
@@ -8,4 +8,18 @@
 	</description>
 	<tutorials>
 	</tutorials>
+	<methods>
+		<method name="_instantiate_playback" qualifiers="virtual">
+			<return type="VideoStreamPlayback" />
+			<description>
+				Called when the video starts playing, to initialize and return a subclass of [VideoStreamPlayback].
+			</description>
+		</method>
+	</methods>
+	<members>
+		<member name="file" type="String" setter="set_file" getter="get_file" default="&quot;&quot;">
+			The video file path or URI that this [VideoStream] resource handles.
+			For [VideoStreamTheora], this filename should be an Ogg Theora video file with the [code].ogv[/code] extension.
+		</member>
+	</members>
 </class>
diff --git a/doc/classes/VideoStreamPlayback.xml b/doc/classes/VideoStreamPlayback.xml
new file mode 100644
index 0000000000..8d8b4fe5b1
--- /dev/null
+++ b/doc/classes/VideoStreamPlayback.xml
@@ -0,0 +1,104 @@
+<?xml version="1.0" encoding="UTF-8" ?>
+<class name="VideoStreamPlayback" inherits="Resource" version="4.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="../class.xsd">
+	<brief_description>
+		Internal class used by [VideoStream] to manage playback state when played from a [VideoStreamPlayer].
+	</brief_description>
+	<description>
+		This class is intended to be overridden by video decoder extensions with custom implementations of [VideoStream].
+	</description>
+	<tutorials>
+	</tutorials>
+	<methods>
+		<method name="_get_channels" qualifiers="virtual const">
+			<return type="int" />
+			<description>
+				Returns the number of audio channels.
+			</description>
+		</method>
+		<method name="_get_length" qualifiers="virtual const">
+			<return type="float" />
+			<description>
+				Returns the video duration in seconds, if known, or 0 if unknown.
+			</description>
+		</method>
+		<method name="_get_mix_rate" qualifiers="virtual const">
+			<return type="int" />
+			<description>
+				Returns the audio sample rate used for mixing.
+			</description>
+		</method>
+		<method name="_get_playback_position" qualifiers="virtual const">
+			<return type="float" />
+			<description>
+				Return the current playback timestamp. Called in response to the [member VideoStreamPlayer.stream_position] getter.
+			</description>
+		</method>
+		<method name="_get_texture" qualifiers="virtual const">
+			<return type="Texture2D" />
+			<description>
+				Allocates a [Texture2D] in which decoded video frames will be drawn.
+			</description>
+		</method>
+		<method name="_is_paused" qualifiers="virtual const">
+			<return type="bool" />
+			<description>
+				Returns the paused status, as set by [method _set_paused].
+			</description>
+		</method>
+		<method name="_is_playing" qualifiers="virtual const">
+			<return type="bool" />
+			<description>
+				Returns the playback state, as determined by calls to [method _play] and [method _stop].
+			</description>
+		</method>
+		<method name="_play" qualifiers="virtual">
+			<return type="void" />
+			<description>
+				Called in response to [member VideoStreamPlayer.autoplay] or [method VideoStreamPlayer.play]. Note that manual playback may also invoke [method _stop] multiple times before this method is called. [method _is_playing] should return true once playing.
+			</description>
+		</method>
+		<method name="_seek" qualifiers="virtual">
+			<return type="void" />
+			<param index="0" name="time" type="float" />
+			<description>
+				Seeks to [code]time[/code] seconds. Called in response to the [member VideoStreamPlayer.stream_position] setter.
+			</description>
+		</method>
+		<method name="_set_audio_track" qualifiers="virtual">
+			<return type="void" />
+			<param index="0" name="idx" type="int" />
+			<description>
+				Select the audio track [code]idx[/code]. Called when playback starts, and in response to the [member VideoStreamPlayer.audio_track] setter.
+			</description>
+		</method>
+		<method name="_set_paused" qualifiers="virtual">
+			<return type="void" />
+			<param index="0" name="paused" type="bool" />
+			<description>
+				Set the paused status of video playback. [method _is_paused] must return [code]paused[/code]. Called in response to the [member VideoStreamPlayer.paused] setter.
+			</description>
+		</method>
+		<method name="_stop" qualifiers="virtual">
+			<return type="void" />
+			<description>
+				Stops playback. May be called multiple times before [method _play], or in response to [method VideoStreamPlayer.stop]. [method _is_playing] should return false once stopped.
+			</description>
+		</method>
+		<method name="_update" qualifiers="virtual">
+			<return type="void" />
+			<param index="0" name="delta" type="float" />
+			<description>
+				Ticks video playback for [code]delta[/code] seconds. Called every frame as long as [method _is_paused] and [method _is_playing] return true.
+			</description>
+		</method>
+		<method name="mix_audio">
+			<return type="int" />
+			<param index="0" name="num_frames" type="int" />
+			<param index="1" name="buffer" type="PackedFloat32Array" default="PackedFloat32Array()" />
+			<param index="2" name="offset" type="int" default="0" />
+			<description>
+				Render [code]num_frames[/code] audio frames (of [method _get_channels] floats each) from [code]buffer[/code], starting from index [code]offset[/code] in the array. Returns the number of audio frames rendered, or -1 on error.
+			</description>
+		</method>
+	</methods>
+</class>
diff --git a/modules/theora/doc_classes/VideoStreamTheora.xml b/modules/theora/doc_classes/VideoStreamTheora.xml
index e07af8f169..3ec762a880 100644
--- a/modules/theora/doc_classes/VideoStreamTheora.xml
+++ b/modules/theora/doc_classes/VideoStreamTheora.xml
@@ -9,19 +9,4 @@
 	</description>
 	<tutorials>
 	</tutorials>
-	<methods>
-		<method name="get_file">
-			<return type="String" />
-			<description>
-				Returns the Ogg Theora video file handled by this [VideoStreamTheora].
-			</description>
-		</method>
-		<method name="set_file">
-			<return type="void" />
-			<param index="0" name="file" type="String" />
-			<description>
-				Sets the Ogg Theora video file that this [VideoStreamTheora] resource handles. The [code]file[/code] name should have the [code].ogv[/code] extension.
-			</description>
-		</method>
-	</methods>
 </class>
diff --git a/modules/theora/video_stream_theora.cpp b/modules/theora/video_stream_theora.cpp
index c600924a3e..b38f7225a2 100644
--- a/modules/theora/video_stream_theora.cpp
+++ b/modules/theora/video_stream_theora.cpp
@@ -574,25 +574,10 @@ bool VideoStreamPlaybackTheora::is_paused() const {
 	return paused;
 }
 
-void VideoStreamPlaybackTheora::set_loop(bool p_enable) {
-}
-
-bool VideoStreamPlaybackTheora::has_loop() const {
-	return false;
-}
-
 double VideoStreamPlaybackTheora::get_length() const {
 	return 0;
 }
 
-String VideoStreamPlaybackTheora::get_stream_name() const {
-	return "";
-}
-
-int VideoStreamPlaybackTheora::get_loop_count() const {
-	return 0;
-}
-
 double VideoStreamPlaybackTheora::get_playback_position() const {
 	return get_time();
 }
@@ -601,11 +586,6 @@ void VideoStreamPlaybackTheora::seek(double p_time) {
 	WARN_PRINT_ONCE("Seeking in Theora videos is not implemented yet (it's only supported for GDExtension-provided video streams).");
 }
 
-void VideoStreamPlaybackTheora::set_mix_callback(AudioMixCallback p_callback, void *p_userdata) {
-	mix_callback = p_callback;
-	mix_udata = p_userdata;
-}
-
 int VideoStreamPlaybackTheora::get_channels() const {
 	return vi.channels;
 }
@@ -657,16 +637,9 @@ VideoStreamPlaybackTheora::~VideoStreamPlaybackTheora() {
 	memdelete(thread_sem);
 #endif
 	clear();
-}
-
-void VideoStreamTheora::_bind_methods() {
-	ClassDB::bind_method(D_METHOD("set_file", "file"), &VideoStreamTheora::set_file);
-	ClassDB::bind_method(D_METHOD("get_file"), &VideoStreamTheora::get_file);
-
-	ADD_PROPERTY(PropertyInfo(Variant::STRING, "file", PROPERTY_HINT_NONE, "", PROPERTY_USAGE_NO_EDITOR | PROPERTY_USAGE_INTERNAL), "set_file", "get_file");
-}
+};
 
-////////////
+void VideoStreamTheora::_bind_methods() {}
 
 Ref<Resource> ResourceFormatLoaderTheora::load(const String &p_path, const String &p_original_path, Error *r_error, bool p_use_sub_threads, float *r_progress, CacheMode p_cache_mode) {
 	Ref<FileAccess> f = FileAccess::open(p_path, FileAccess::READ);
diff --git a/modules/theora/video_stream_theora.h b/modules/theora/video_stream_theora.h
index f047440df7..32adc28a88 100644
--- a/modules/theora/video_stream_theora.h
+++ b/modules/theora/video_stream_theora.h
@@ -99,8 +99,6 @@ class VideoStreamPlaybackTheora : public VideoStreamPlayback {
 
 	Ref<ImageTexture> texture;
 
-	AudioMixCallback mix_callback = nullptr;
-	void *mix_udata = nullptr;
 	bool paused = false;
 
 #ifdef THEORA_USE_THREAD_STREAMING
@@ -133,15 +131,8 @@ public:
 	virtual void set_paused(bool p_paused) override;
 	virtual bool is_paused() const override;
 
-	virtual void set_loop(bool p_enable) override;
-	virtual bool has_loop() const override;
-
 	virtual double get_length() const override;
 
-	virtual String get_stream_name() const;
-
-	virtual int get_loop_count() const;
-
 	virtual double get_playback_position() const override;
 	virtual void seek(double p_time) override;
 
@@ -150,7 +141,6 @@ public:
 	virtual Ref<Texture2D> get_texture() const override;
 	virtual void update(double p_delta) override;
 
-	virtual void set_mix_callback(AudioMixCallback p_callback, void *p_userdata) override;
 	virtual int get_channels() const override;
 	virtual int get_mix_rate() const override;
 
@@ -163,9 +153,6 @@ public:
 class VideoStreamTheora : public VideoStream {
 	GDCLASS(VideoStreamTheora, VideoStream);
 
-	String file;
-	int audio_track;
-
 protected:
 	static void _bind_methods();
 
@@ -177,8 +164,6 @@ public:
 		return pb;
 	}
 
-	void set_file(const String &p_file) { file = p_file; }
-	String get_file() { return file; }
 	void set_audio_track(int p_track) override { audio_track = p_track; }
 
 	VideoStreamTheora() { audio_track = 0; }
diff --git a/scene/gui/video_stream_player.cpp b/scene/gui/video_stream_player.cpp
index 6eb25bf852..1f3bbff779 100644
--- a/scene/gui/video_stream_player.cpp
+++ b/scene/gui/video_stream_player.cpp
@@ -236,7 +236,6 @@ void VideoStreamPlayer::set_stream(const Ref<VideoStream> &p_stream) {
 	AudioServer::get_singleton()->unlock();
 
 	if (!playback.is_null()) {
-		playback->set_loop(loops);
 		playback->set_paused(paused);
 		texture = playback->get_texture();
 
@@ -344,6 +343,12 @@ int VideoStreamPlayer::get_buffering_msec() const {
 
 void VideoStreamPlayer::set_audio_track(int p_track) {
 	audio_track = p_track;
+	if (stream.is_valid()) {
+		stream->set_audio_track(audio_track);
+	}
+	if (playback.is_valid()) {
+		playback->set_audio_track(audio_track);
+	}
 }
 
 int VideoStreamPlayer::get_audio_track() const {
diff --git a/scene/gui/video_stream_player.h b/scene/gui/video_stream_player.h
index 09ef272a9a..1fd599a9e1 100644
--- a/scene/gui/video_stream_player.h
+++ b/scene/gui/video_stream_player.h
@@ -65,7 +65,6 @@ class VideoStreamPlayer : public Control {
 	float volume = 1.0;
 	double last_audio_time = 0.0;
 	bool expand = false;
-	bool loops = false;
 	int buffering_ms = 500;
 	int audio_track = 0;
 	int bus_index = 0;
diff --git a/scene/register_scene_types.cpp b/scene/register_scene_types.cpp
index 7bebf1cfd3..39fc03f9f1 100644
--- a/scene/register_scene_types.cpp
+++ b/scene/register_scene_types.cpp
@@ -393,6 +393,8 @@ void register_scene_types() {
 
 	GDREGISTER_CLASS(LineEdit);
 	GDREGISTER_CLASS(VideoStreamPlayer);
+	GDREGISTER_VIRTUAL_CLASS(VideoStreamPlayback);
+	GDREGISTER_VIRTUAL_CLASS(VideoStream);
 
 #ifndef ADVANCED_GUI_DISABLED
 	GDREGISTER_CLASS(FileDialog);
@@ -906,7 +908,6 @@ void register_scene_types() {
 #ifndef _3D_DISABLED
 	GDREGISTER_CLASS(AudioStreamPlayer3D);
 #endif
-	GDREGISTER_ABSTRACT_CLASS(VideoStream);
 	GDREGISTER_CLASS(AudioStreamWAV);
 	GDREGISTER_CLASS(AudioStreamPolyphonic);
 	GDREGISTER_ABSTRACT_CLASS(AudioStreamPlaybackPolyphonic);
diff --git a/scene/resources/video_stream.cpp b/scene/resources/video_stream.cpp
new file mode 100644
index 0000000000..ee1a47c338
--- /dev/null
+++ b/scene/resources/video_stream.cpp
@@ -0,0 +1,198 @@
+/**************************************************************************/
+/*  video_stream.cpp                                                      */
+/**************************************************************************/
+/*                         This file is part of:                          */
+/*                             GODOT ENGINE                               */
+/*                        https://godotengine.org                         */
+/**************************************************************************/
+/* Copyright (c) 2014-present Godot Engine contributors (see AUTHORS.md). */
+/* Copyright (c) 2007-2014 Juan Linietsky, Ariel Manzur.                  */
+/*                                                                        */
+/* Permission is hereby granted, free of charge, to any person obtaining  */
+/* a copy of this software and associated documentation files (the        */
+/* "Software"), to deal in the Software without restriction, including    */
+/* without limitation the rights to use, copy, modify, merge, publish,    */
+/* distribute, sublicense, and/or sell copies of the Software, and to     */
+/* permit persons to whom the Software is furnished to do so, subject to  */
+/* the following conditions:                                              */
+/*                                                                        */
+/* The above copyright notice and this permission notice shall be         */
+/* included in all copies or substantial portions of the Software.        */
+/*                                                                        */
+/* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,        */
+/* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF     */
+/* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. */
+/* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY   */
+/* CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,   */
+/* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE      */
+/* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.                 */
+/**************************************************************************/
+
+#include "video_stream.h"
+
+#include "core/config/project_settings.h"
+#include "servers/audio_server.h"
+
+// VideoStreamPlayback starts here.
+
+void VideoStreamPlayback::_bind_methods() {
+	ClassDB::bind_method(D_METHOD("mix_audio", "num_frames", "buffer", "offset"), &VideoStreamPlayback::mix_audio, DEFVAL(PackedFloat32Array()), DEFVAL(0));
+	GDVIRTUAL_BIND(_stop);
+	GDVIRTUAL_BIND(_play);
+	GDVIRTUAL_BIND(_is_playing);
+	GDVIRTUAL_BIND(_set_paused, "paused");
+	GDVIRTUAL_BIND(_is_paused);
+	GDVIRTUAL_BIND(_get_length);
+	GDVIRTUAL_BIND(_get_playback_position);
+	GDVIRTUAL_BIND(_seek, "time");
+	GDVIRTUAL_BIND(_set_audio_track, "idx");
+	GDVIRTUAL_BIND(_get_texture);
+	GDVIRTUAL_BIND(_update, "delta");
+	GDVIRTUAL_BIND(_get_channels);
+	GDVIRTUAL_BIND(_get_mix_rate);
+}
+
+VideoStreamPlayback::VideoStreamPlayback() {
+}
+
+VideoStreamPlayback::~VideoStreamPlayback() {
+}
+
+void VideoStreamPlayback::stop() {
+	GDVIRTUAL_CALL(_stop);
+}
+
+void VideoStreamPlayback::play() {
+	GDVIRTUAL_CALL(_play);
+}
+
+bool VideoStreamPlayback::is_playing() const {
+	bool ret;
+	if (GDVIRTUAL_CALL(_is_playing, ret)) {
+		return ret;
+	}
+	return false;
+}
+
+void VideoStreamPlayback::set_paused(bool p_paused) {
+	GDVIRTUAL_CALL(_is_playing, p_paused);
+}
+
+bool VideoStreamPlayback::is_paused() const {
+	bool ret;
+	if (GDVIRTUAL_CALL(_is_paused, ret)) {
+		return ret;
+	}
+	return false;
+}
+
+double VideoStreamPlayback::get_length() const {
+	double ret;
+	if (GDVIRTUAL_CALL(_get_length, ret)) {
+		return ret;
+	}
+	return 0;
+}
+
+double VideoStreamPlayback::get_playback_position() const {
+	double ret;
+	if (GDVIRTUAL_CALL(_get_playback_position, ret)) {
+		return ret;
+	}
+	return 0;
+}
+
+void VideoStreamPlayback::seek(double p_time) {
+	GDVIRTUAL_CALL(_seek, p_time);
+}
+
+void VideoStreamPlayback::set_audio_track(int p_idx) {
+	GDVIRTUAL_CALL(_set_audio_track, p_idx);
+}
+
+Ref<Texture2D> VideoStreamPlayback::get_texture() const {
+	Ref<Texture2D> ret;
+	if (GDVIRTUAL_CALL(_get_texture, ret)) {
+		return ret;
+	}
+	return nullptr;
+}
+
+void VideoStreamPlayback::update(double p_delta) {
+	if (!GDVIRTUAL_CALL(_update, p_delta)) {
+		ERR_FAIL_MSG("VideoStreamPlayback::update unimplemented");
+	}
+}
+
+void VideoStreamPlayback::set_mix_callback(AudioMixCallback p_callback, void *p_userdata) {
+	mix_callback = p_callback;
+	mix_udata = p_userdata;
+}
+
+int VideoStreamPlayback::get_channels() const {
+	int ret;
+	if (GDVIRTUAL_CALL(_get_channels, ret)) {
+		_channel_count = ret;
+		return ret;
+	}
+	return 0;
+}
+
+int VideoStreamPlayback::get_mix_rate() const {
+	int ret;
+	if (GDVIRTUAL_CALL(_get_mix_rate, ret)) {
+		return ret;
+	}
+	return 0;
+}
+
+int VideoStreamPlayback::mix_audio(int num_frames, PackedFloat32Array buffer, int offset) {
+	if (num_frames <= 0) {
+		return 0;
+	}
+	if (!mix_callback) {
+		return -1;
+	}
+	ERR_FAIL_INDEX_V(offset, buffer.size(), -1);
+	ERR_FAIL_INDEX_V((_channel_count < 1 ? 1 : _channel_count) * num_frames - 1, buffer.size() - offset, -1);
+	return mix_callback(mix_udata, buffer.ptr() + offset, num_frames);
+}
+
+/* --- NOTE VideoStream starts here. ----- */
+
+Ref<VideoStreamPlayback> VideoStream::instantiate_playback() {
+	Ref<VideoStreamPlayback> ret;
+	if (GDVIRTUAL_CALL(_instantiate_playback, ret)) {
+		ERR_FAIL_COND_V_MSG(ret.is_null(), nullptr, "Plugin returned null playback");
+		ret->set_audio_track(audio_track);
+		return ret;
+	}
+	return nullptr;
+}
+
+void VideoStream::set_file(const String &p_file) {
+	file = p_file;
+}
+
+String VideoStream::get_file() {
+	return file;
+}
+
+void VideoStream::_bind_methods() {
+	ClassDB::bind_method(D_METHOD("set_file", "file"), &VideoStream::set_file);
+	ClassDB::bind_method(D_METHOD("get_file"), &VideoStream::get_file);
+
+	ADD_PROPERTY(PropertyInfo(Variant::STRING, "file"), "set_file", "get_file");
+
+	GDVIRTUAL_BIND(_instantiate_playback);
+}
+
+VideoStream::VideoStream() {
+}
+
+VideoStream::~VideoStream() {
+}
+
+void VideoStream::set_audio_track(int p_track) {
+	audio_track = p_track;
+}
diff --git a/scene/resources/video_stream.h b/scene/resources/video_stream.h
index f83c621d0a..b91a7acf35 100644
--- a/scene/resources/video_stream.h
+++ b/scene/resources/video_stream.h
@@ -31,6 +31,7 @@
 #ifndef VIDEO_STREAM_H
 #define VIDEO_STREAM_H
 
+#include "core/io/file_access.h"
 #include "scene/resources/texture.h"
 
 class VideoStreamPlayback : public Resource {
@@ -39,40 +40,77 @@ class VideoStreamPlayback : public Resource {
 public:
 	typedef int (*AudioMixCallback)(void *p_udata, const float *p_data, int p_frames);
 
-	virtual void stop() = 0;
-	virtual void play() = 0;
+protected:
+	AudioMixCallback mix_callback = nullptr;
+	void *mix_udata = nullptr;
+	mutable int _channel_count = 0; // Used only to assist with bounds checking in mix_audio.
+
+	static void _bind_methods();
+	GDVIRTUAL0(_stop);
+	GDVIRTUAL0(_play);
+	GDVIRTUAL0RC(bool, _is_playing);
+	GDVIRTUAL1(_set_paused, bool);
+	GDVIRTUAL0RC(bool, _is_paused);
+	GDVIRTUAL0RC(double, _get_length);
+	GDVIRTUAL0RC(double, _get_playback_position);
+	GDVIRTUAL1(_seek, double);
+	GDVIRTUAL1(_set_audio_track, int);
+	GDVIRTUAL0RC(Ref<Texture2D>, _get_texture);
+	GDVIRTUAL1(_update, double);
+	GDVIRTUAL0RC(int, _get_channels);
+	GDVIRTUAL0RC(int, _get_mix_rate);
+
+	int mix_audio(int num_frames, PackedFloat32Array buffer = {}, int offset = 0);
 
-	virtual bool is_playing() const = 0;
+public:
+	VideoStreamPlayback();
+	virtual ~VideoStreamPlayback();
 
-	virtual void set_paused(bool p_paused) = 0;
-	virtual bool is_paused() const = 0;
+	virtual void stop();
+	virtual void play();
 
-	virtual void set_loop(bool p_enable) = 0;
-	virtual bool has_loop() const = 0;
+	virtual bool is_playing() const;
 
-	virtual double get_length() const = 0;
+	virtual void set_paused(bool p_paused);
+	virtual bool is_paused() const;
 
-	virtual double get_playback_position() const = 0;
-	virtual void seek(double p_time) = 0;
+	virtual double get_length() const;
 
-	virtual void set_audio_track(int p_idx) = 0;
+	virtual double get_playback_position() const;
+	virtual void seek(double p_time);
 
-	virtual Ref<Texture2D> get_texture() const = 0;
+	virtual void set_audio_track(int p_idx);
 
-	virtual void update(double p_delta) = 0;
+	virtual Ref<Texture2D> get_texture() const;
+	virtual void update(double p_delta);
 
-	virtual void set_mix_callback(AudioMixCallback p_callback, void *p_userdata) = 0;
-	virtual int get_channels() const = 0;
-	virtual int get_mix_rate() const = 0;
+	virtual void set_mix_callback(AudioMixCallback p_callback, void *p_userdata);
+	virtual int get_channels() const;
+	virtual int get_mix_rate() const;
 };
 
 class VideoStream : public Resource {
 	GDCLASS(VideoStream, Resource);
-	OBJ_SAVE_TYPE(VideoStream); // Saves derived classes with common type so they can be interchanged.
+	OBJ_SAVE_TYPE(VideoStream);
+
+protected:
+	static void
+	_bind_methods();
+
+	GDVIRTUAL0R(Ref<VideoStreamPlayback>, _instantiate_playback);
+
+	String file;
+	int audio_track = 0;
 
 public:
-	virtual void set_audio_track(int p_track) = 0;
-	virtual Ref<VideoStreamPlayback> instantiate_playback() = 0;
+	void set_file(const String &p_file);
+	String get_file();
+
+	virtual void set_audio_track(int p_track);
+	virtual Ref<VideoStreamPlayback> instantiate_playback();
+
+	VideoStream();
+	~VideoStream();
 };
 
 #endif // VIDEO_STREAM_H