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Centricular Ltd
Nirbheek Chauhan(nirbheek on IRC)
GNOME contributor since 2007
http://[email protected]
Centricular Ltd
An introduction to using GStreamerin your GNOME application
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What is GStreamer?
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GStreamer 1.0
GStreamer 0.10
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How does it work?
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filter2
sink src
filter1
sink src
bin
sink
sink
source
src
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pipeline
mp3 decoder
sink src
audio sink
sink
file source
src
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How do you use it?
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gst-launch-1.0
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$ gst-launch-1.0 \ filesrc location=audio.mp3 ! \ mad ! \ pulsesink
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GstElement *pipeline;GstElement *src, *decoder, *sink;
gst_init (&argc, &argv);
src = gst_element_factory_make ("filesrc", NULL);decoder = gst_element_factory_make ("mad", NULL);sink = gst_element_factory_make ("pulsesink", NULL);
g_object_set (src, "location", "audio.mp3", NULL);
pipeline = gst_pipeline_new ();gst_bin_add_many (GST_BIN (pipeline), src, decoder,
sink, NULL);gst_element_link_many (src, decoder, sink, NULL);gst_element_set_state (pipeline, GST_STATE_PLAYING);
do {} while (1); /* Wait forever */
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Element States
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Element States
NULL READY PAUSED PLAYING→ → →
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Element States
PLAYING PAUSED PLAYING→ →
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Element States
PLAYING [...] NULL→ →
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Video files?
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“Sometimes” pads.
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pipeline
URI Decoder queue
sink src
audio sink
sinksrc_0
queue
sink src
video sink
sinksrc_1
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$ gst-launch-1.0 \ uridecodebin name=d \ uri=file://.../video.mp4 \ d. ! queue ! pulsesink \ d. ! queue ! xvimagesink
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GstElement *pipeline, *d;
gst_init (&argc, &argv);
d = gst_element_factory_make ("uridecodebin", NULL);g_object_set (d, "uri", "file://.../video.mp4", NULL);
pipeline = gst_pipeline_new ();
gst_bin_add (GST_BIN (pipeline), d);
g_signal_connect (d, "pad-added", pad_added_cb,pipeline);
gst_element_set_state (pipeline, GST_STATE_PLAYING);
do {} while (1); /* Wait forever */
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static voidpad_added_cb (GstElement * d, GstPad * newsrcpad,
GstElement * pipeline){
GstCaps *caps;GstStructure *s;
caps = gst_pad_get_current_caps (newsrcpad);s = gst_caps_get_structure (caps, 0);if (gst_structure_has_name (s, "audio/x-raw"))
pipeline_add_audio_sink (pipeline, newsrcpad); else if (gst_structure_has_name (s, "video/x-raw"))
pipeline_add_video_sink (pipeline, newsrcpad);
gst_caps_unref (caps);/* ignore other types of pads */
}
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What the hell are “caps”?!
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static voidpad_added_cb (GstElement * d, GstPad * newsrcpad,
GstElement * pipeline){
GstCaps *caps;GstStructure *s;
caps = gst_pad_get_current_caps (newsrcpad);s = gst_caps_get_structure (caps, 0);if (gst_structure_has_name (s, "audio/x-raw"))
pipeline_add_audio_sink (pipeline, newsrcpad); else if (gst_structure_has_name (s, "video/x-raw"))
pipeline_add_video_sink (pipeline, newsrcpad);
gst_caps_unref (caps);/* ignore other types of pads */
}
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static voidpipeline_add_audio_sink (GstElement * pipeline,
GstPad * srcpad){
GstElement *q, *sink;GstPad *sinkpad;
q = gst_element_factory_make ("queue", NULL);sink = gst_element_factory_make ("pulsesink", NULL);gst_bin_add_many (GST_BIN (pipeline), q, sink, NULL);
sinkpad = gst_element_get_static_pad (q, "sink");gst_pad_link (srcpad, sinkpad)gst_element_link (q, sink);
gst_element_sync_state_with_parent (q);gst_element_sync_state_with_parent (sink);gst_object_unref (sinkpad);
}
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static voidpipeline_add_video_sink (GstElement * pipeline,
GstPad * srcpad){
GstElement *q, *sink;GstPad *sinkpad;
q = gst_element_factory_make ("queue", NULL);sink = gst_element_factory_make ("xvimagesink", NULL);gst_bin_add_many (GST_BIN (pipeline), q, sink, NULL);
sinkpad = gst_element_get_static_pad (q, "sink");gst_pad_link (srcpad, sinkpad)gst_element_link (q, sink);
gst_element_sync_state_with_parent (q);gst_element_sync_state_with_parent (sink);gst_object_unref (sinkpad);
}
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Seems like a lot of work for something so common
☹
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playbin
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$ gst-launch-1.0 playbin uri=file://.../video.mp4
$ gst-launch-1.0 playbin uri=http://.../audio.mp3
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GstElement *playbin;
gst_init (&argc, &argv);
playbin = gst_element_factory_make ("playbin", NULL);g_object_set (p, "uri", "file://.../video.mp4", NULL);
gst_element_set_state (playbin, GST_STATE_PLAYING);
do {} while (1); /* Wait forever */
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One more thing.
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Static Pads & Request Pads
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$ gst-launch-1.0 \ qtmux name=m ! filesink location=file.mp4 \ pulsesrc ! queue ! faac ! m. \ v4l2src ! queue ! x264enc ! m.
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/* Insert similar code as earlier slides */
srcpad = gst_element_get_static_pad (faac, "src");audio_pad = gst_element_get_request_pad (qtmux,
"audio_%d");gst_pad_link (srcpad, audio_pad);
srcpad = gst_element_get_static_pad (x264enc, "src");video_pad = gst_element_get_request_pad (qtmux,
"video_%d");gst_pad_link (srcpad, video_pad);
gst_element_set_state (pipeline, GST_STATE_PLAYING);
do {} while (1); /* Wait forever */
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I lied. There’s a lot more.GStreamer is quite versatile!
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Events, Queries, MessagesAction Signals, Pad Probes, Threading
Mainloop integration, Platform-specific quirks...
45 min is only enough for a taste.
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The rest is left as an exercise for the reader.
☺
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Too much?
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$ gst-play-1.0 file://.../video.mp4
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$ gst-launch-1.0 playbin uri=file://.../video.mp4
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GstElement *playbin;
gst_init (&argc, &argv);
playbin = gst_element_factory_make ("playbin", NULL);g_object_set (p, "uri", "file://.../video.mp4", NULL);
gst_element_set_state (playbin, GST_STATE_PLAYING);
do {} while (1); /* Wait forever */
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Questions?
