Update
This commit is contained in:
Akkariin Meiko
@@ -0,0 +1,259 @@
|
||||
# Playback tutorial 6: Audio visualization
|
||||
|
||||
|
||||
{{ ALERT_PY.md }}
|
||||
|
||||
{{ ALERT_JS.md }}
|
||||
|
||||
## Goal
|
||||
|
||||
GStreamer comes with a set of elements that turn audio into video. They
|
||||
can be used for scientific visualization or to spice up your music
|
||||
player, for example. This tutorial shows:
|
||||
|
||||
- How to enable audio visualization
|
||||
- How to select the visualization element
|
||||
|
||||
## Introduction
|
||||
|
||||
Enabling audio visualization in `playbin` is actually very easy. Just
|
||||
set the appropriate `playbin` flag and, when an audio-only stream is
|
||||
found, it will instantiate the necessary elements to create and display
|
||||
the visualization.
|
||||
|
||||
If you want to specify the actual element that you want to use to
|
||||
generate the visualization, you instantiate it yourself and then tell
|
||||
`playbin` about it through the `vis-plugin` property.
|
||||
|
||||
This tutorial searches the GStreamer registry for all the elements of
|
||||
the Visualization class, tries to select `goom` (or another one if it is
|
||||
not available) and passes it to `playbin`.
|
||||
|
||||
## A fancy music player
|
||||
|
||||
Copy this code into a text file named `playback-tutorial-6.c`.
|
||||
|
||||
**playback-tutorial-6.c**
|
||||
|
||||
``` c
|
||||
#include <gst/gst.h>
|
||||
|
||||
/* playbin flags */
|
||||
typedef enum {
|
||||
GST_PLAY_FLAG_VIS = (1 << 3) /* Enable rendering of visualizations when there is no video stream. */
|
||||
} GstPlayFlags;
|
||||
|
||||
/* Return TRUE if this is a Visualization element */
|
||||
static gboolean filter_vis_features (GstPluginFeature *feature, gpointer data) {
|
||||
GstElementFactory *factory;
|
||||
|
||||
if (!GST_IS_ELEMENT_FACTORY (feature))
|
||||
return FALSE;
|
||||
factory = GST_ELEMENT_FACTORY (feature);
|
||||
if (!g_strrstr (gst_element_factory_get_klass (factory), "Visualization"))
|
||||
return FALSE;
|
||||
|
||||
return TRUE;
|
||||
}
|
||||
|
||||
int main(int argc, char *argv[]) {
|
||||
GstElement *pipeline, *vis_plugin;
|
||||
GstBus *bus;
|
||||
GstMessage *msg;
|
||||
GList *list, *walk;
|
||||
GstElementFactory *selected_factory = NULL;
|
||||
guint flags;
|
||||
|
||||
/* Initialize GStreamer */
|
||||
gst_init (&argc, &argv);
|
||||
|
||||
/* Get a list of all visualization plugins */
|
||||
list = gst_registry_feature_filter (gst_registry_get (), filter_vis_features, FALSE, NULL);
|
||||
|
||||
/* Print their names */
|
||||
g_print("Available visualization plugins:\n");
|
||||
for (walk = list; walk != NULL; walk = g_list_next (walk)) {
|
||||
const gchar *name;
|
||||
GstElementFactory *factory;
|
||||
|
||||
factory = GST_ELEMENT_FACTORY (walk->data);
|
||||
name = gst_element_factory_get_longname (factory);
|
||||
g_print(" %s\n", name);
|
||||
|
||||
if (selected_factory == NULL || g_str_has_prefix (name, "GOOM")) {
|
||||
selected_factory = factory;
|
||||
}
|
||||
}
|
||||
|
||||
/* Don't use the factory if it's still empty */
|
||||
/* e.g. no visualization plugins found */
|
||||
if (!selected_factory) {
|
||||
g_print ("No visualization plugins found!\n");
|
||||
return -1;
|
||||
}
|
||||
|
||||
/* We have now selected a factory for the visualization element */
|
||||
g_print ("Selected '%s'\n", gst_element_factory_get_longname (selected_factory));
|
||||
vis_plugin = gst_element_factory_create (selected_factory, NULL);
|
||||
if (!vis_plugin)
|
||||
return -1;
|
||||
|
||||
/* Build the pipeline */
|
||||
pipeline = gst_parse_launch ("playbin uri=http://radio.hbr1.com:19800/ambient.ogg", NULL);
|
||||
|
||||
/* Set the visualization flag */
|
||||
g_object_get (pipeline, "flags", &flags, NULL);
|
||||
flags |= GST_PLAY_FLAG_VIS;
|
||||
g_object_set (pipeline, "flags", flags, NULL);
|
||||
|
||||
/* set vis plugin for playbin */
|
||||
g_object_set (pipeline, "vis-plugin", vis_plugin, NULL);
|
||||
|
||||
/* Start playing */
|
||||
gst_element_set_state (pipeline, GST_STATE_PLAYING);
|
||||
|
||||
/* Wait until error or EOS */
|
||||
bus = gst_element_get_bus (pipeline);
|
||||
msg = gst_bus_timed_pop_filtered (bus, GST_CLOCK_TIME_NONE, GST_MESSAGE_ERROR | GST_MESSAGE_EOS);
|
||||
|
||||
/* Free resources */
|
||||
if (msg != NULL)
|
||||
gst_message_unref (msg);
|
||||
gst_plugin_feature_list_free (list);
|
||||
gst_object_unref (bus);
|
||||
gst_element_set_state (pipeline, GST_STATE_NULL);
|
||||
gst_object_unref (pipeline);
|
||||
return 0;
|
||||
}
|
||||
```
|
||||
|
||||
> ![information] If you need help to compile this code, refer to the
|
||||
> **Building the tutorials** section for your platform: [Mac] or
|
||||
> [Windows] or use this specific command on Linux:
|
||||
>
|
||||
> `` gcc playback-tutorial-6.c -o playback-tutorial-6 `pkg-config --cflags --libs gstreamer-1.0` ``
|
||||
>
|
||||
> If you need help to run this code, refer to the **Running the
|
||||
> tutorials** section for your platform: [Mac OS X], [Windows][1], for
|
||||
> [iOS] or for [android].
|
||||
>
|
||||
> This tutorial plays music streamed from the [HBR1](http://www.hbr1.com/) Internet radio station. A window should open displaying somewhat psychedelic color patterns moving with the music. The media is fetched from the Internet, so the window might take a few seconds to appear, depending on your connection speed.
|
||||
>
|
||||
> Required libraries: `gstreamer-1.0`
|
||||
|
||||
## Walkthrough
|
||||
|
||||
First off, we indicate `playbin` that we want an audio visualization by
|
||||
setting the `GST_PLAY_FLAG_VIS` flag. If the media already contains
|
||||
video, this flag has no effect.
|
||||
|
||||
``` c
|
||||
/* Set the visualization flag */
|
||||
g_object_get (pipeline, "flags", &flags, NULL);
|
||||
flags |= GST_PLAY_FLAG_VIS;
|
||||
g_object_set (pipeline, "flags", flags, NULL);
|
||||
```
|
||||
|
||||
If no visualization plugin is enforced by the user, `playbin` will use
|
||||
`goom` (audio visualization will be disabled if `goom` is not
|
||||
available). The rest of the tutorial shows how to find out the available
|
||||
visualization elements and enforce one to `playbin`.
|
||||
|
||||
``` c
|
||||
/* Get a list of all visualization plugins */
|
||||
list = gst_registry_feature_filter (gst_registry_get (), filter_vis_features, FALSE, NULL);
|
||||
```
|
||||
|
||||
`gst_registry_feature_filter()` examines all elements currently in the
|
||||
GStreamer registry and selects those for which
|
||||
the `filter_vis_features` function returns TRUE. This function selects
|
||||
only the Visualization plugins:
|
||||
|
||||
``` c
|
||||
/* Return TRUE if this is a Visualization element */
|
||||
static gboolean filter_vis_features (GstPluginFeature *feature, gpointer data) {
|
||||
GstElementFactory *factory;
|
||||
|
||||
if (!GST_IS_ELEMENT_FACTORY (feature))
|
||||
return FALSE;
|
||||
factory = GST_ELEMENT_FACTORY (feature);
|
||||
if (!g_strrstr (gst_element_factory_get_klass (factory), "Visualization"))
|
||||
return FALSE;
|
||||
|
||||
return TRUE;
|
||||
}
|
||||
```
|
||||
|
||||
A bit of theory regarding the organization of GStreamer elements is in
|
||||
place: Each of the files that GStreamer loads at runtime is known as a
|
||||
Plugin (`GstPlugin`). A Plugin can contain many Features
|
||||
(`GstPluginFeature`). There are different kinds of Features, among them,
|
||||
the Element Factories (`GstElementFactory`) that we have been using to
|
||||
build Elements (`GstElement`).
|
||||
|
||||
This function simply disregards all Features which are not Factories,
|
||||
and then all Factories whose class (obtained with
|
||||
`gst_element_factory_get_klass()`) does not include “Visualization”. As
|
||||
stated in the documentation for `GstElementFactory`, a Factory’s class
|
||||
is a “string describing the type of element, as an unordered list
|
||||
separated with slashes (/)”. Examples of classes are “Source/Network”,
|
||||
“Codec/Decoder/Video”, “Codec/Encoder/Audio” or “Visualization”.
|
||||
|
||||
``` c
|
||||
/* Print their names */
|
||||
g_print("Available visualization plugins:\n");
|
||||
for (walk = list; walk != NULL; walk = g_list_next (walk)) {
|
||||
const gchar *name;
|
||||
GstElementFactory *factory;
|
||||
|
||||
factory = GST_ELEMENT_FACTORY (walk->data);
|
||||
name = gst_element_factory_get_longname (factory);
|
||||
g_print(" %s\n", name);
|
||||
|
||||
if (selected_factory == NULL || g_str_has_prefix (name, "GOOM")) {
|
||||
selected_factory = factory;
|
||||
}
|
||||
}
|
||||
```
|
||||
|
||||
Once we have the list of Visualization plugins, we print their names
|
||||
(`gst_element_factory_get_longname()`) and choose one (in this case,
|
||||
GOOM).
|
||||
|
||||
``` c
|
||||
/* We have now selected a factory for the visualization element */
|
||||
g_print ("Selected '%s'\n", gst_element_factory_get_longname (selected_factory));
|
||||
vis_plugin = gst_element_factory_create (selected_factory, NULL);
|
||||
if (!vis_plugin)
|
||||
return -1;
|
||||
```
|
||||
|
||||
The selected factory is used to instantiate an actual `GstElement` which
|
||||
is then passed to `playbin` through the `vis-plugin` property:
|
||||
|
||||
``` c
|
||||
/* set vis plugin for playbin */
|
||||
g_object_set (pipeline, "vis-plugin", vis_plugin, NULL);
|
||||
```
|
||||
|
||||
And we are done.
|
||||
|
||||
## Conclusion
|
||||
|
||||
This tutorial has shown:
|
||||
|
||||
- How to enable Audio Visualization in `playbin` with the
|
||||
`GST_PLAY_FLAG_VIS` flag
|
||||
- How to enforce one particular visualization element with the
|
||||
`vis-plugin` `playbin` property
|
||||
|
||||
It has been a pleasure having you here, and see you soon\!
|
||||
|
||||
[information]: images/icons/emoticons/information.svg
|
||||
[Mac]: installing/on-mac-osx.md
|
||||
[Windows]: installing/on-windows.md
|
||||
[Mac OS X]: installing/on-mac-osx.md#building-the-tutorials
|
||||
[1]: installing/on-windows.md#running-the-tutorials
|
||||
[iOS]: installing/for-ios-development.md#building-the-tutorials
|
||||
[android]: installing/for-android-development.md#building-the-tutorials
|
||||
[warning]: images/icons/emoticons/warning.svg
|
||||
Reference in New Issue
Block a user