Gstreamer到底是個啥？

GStreamer 是一個 基于pipeline的多媒體框架，基于GObject，以C語言寫成。

應用GStreamer這個這個多媒體框架，你可以寫出任意一種流媒體的應用來如：meidaplayer、音視頻編輯器、VOIP、流媒體服務器、音視頻編碼等等。

關于視頻快進/快退/循環播放的知識總結:

1.本地視頻時長獲取:

Gst.Pad.query_duration官方函數介紹:

def Gst.Pad.query_duration (self, format): #python wrapper for ’gst_pad_query_duration’Queries a pad for the total stream duration.Parameters:pad ( Gst.Pad ) ?a Gst.Pad to invoke the duration query on.format ( Gst.Format ) ?the Gst.Format requestedReturns a tuple made of:( gboolean ) ?TRUE (not introspectable) if the query could be performed.duration ( gint64 ) ?TRUE (not introspectable) if the query could be performed.

使用如下:

pipeline.query_duration(Gst.Format.TIME)[1]

其中pipeline為播放本地視頻的管道,query_duration()函數返回一個元組,元組的形式為[Ture,duration:******]，******為以ns為單位的視頻時長。

2.視頻播放當前位置獲取：

Gst.Pad.query_position官方函數介紹：

def Gst.Pad.query_position (self, format): #python wrapper for ’gst_pad_query_position’Queries a pad for the stream position.Parameters:pad ( Gst.Pad ) ?a Gst.Pad to invoke the position query on.format ( Gst.Format ) ?the Gst.Format requestedReturns a tuple made of:( gboolean ) ?TRUE (not introspectable) if the query could be performed.cur ( gint64 ) ?TRUE (not introspectable) if the query could be performed.

使用方法與時長獲取函數query_duration()相同。

3.播放跳轉函數：

Gst.Element.seek_simple官方函數介紹：

def Gst.Element.seek_simple (self, format, seek_flags, seek_pos): #python wrapper for ’gst_element_seek_simple’ Parameters:element ( Gst.Element ) ?a Gst.Element to seek onformat ( Gst.Format ) ?a Gst.Format to execute the seek in, such as Gst.Format.TIMEseek_flags ( Gst.SeekFlags ) ?seek options; playback applications will usually want to use GST_SEEK_FLAG_FLUSH | GST_SEEK_FLAG_KEY_UNIT hereseek_pos ( gint64 ) ?position to seek to (relative to the start); if you are doing a seek in Gst.Format.TIME this value is in nanoseconds - multiply with Gst.SECOND to convert seconds to nanoseconds or with Gst.MSECOND to convert milliseconds to nanoseconds.Returns ( gboolean ) :TRUE (not introspectable) if the seek operation succeeded. Flushing seeks will trigger a preroll, which will emit Gst.MessageType.ASYNC_DONE.

函數使用樣例：

pipeline.seek_simple(Gst.Format.TIME, Gst.SeekFlags.FLUSH, time)

其中time的單位為nanoseconds。

有視頻快進/快退/循環播放功能的小播放器.

import os, _thread, timeimport gigi.require_version('Gst', '1.0')gi.require_version(’Gtk’, ’3.0’)from gi.repository import Gst, GObject, Gtk, Gdkclass GTK_Main: def __init__(self): window = Gtk.Window(Gtk.WindowType.TOPLEVEL) window.set_title('Vorbis-Player') window.set_default_size(500, -1) window.connect('destroy', Gtk.main_quit, 'WM destroy') vbox = Gtk.VBox() window.add(vbox) self.entry = Gtk.Entry() vbox.pack_start(self.entry, False, False, 0) hbox = Gtk.HBox() vbox.add(hbox) buttonbox = Gtk.HButtonBox() hbox.pack_start(buttonbox, False, False, 0) rewind_button = Gtk.Button('Rewind') rewind_button.connect('clicked', self.rewind_callback) buttonbox.add(rewind_button) self.button = Gtk.Button('Start') self.button.connect('clicked', self.start_stop) buttonbox.add(self.button) forward_button = Gtk.Button('Forward') forward_button.connect('clicked', self.forward_callback) buttonbox.add(forward_button) self.time_label = Gtk.Label() self.time_label.set_text('00:00 / 00:00') hbox.add(self.time_label) window.show_all() self.player = Gst.Pipeline.new('player') source = Gst.ElementFactory.make('filesrc', 'file-source') demuxer = Gst.ElementFactory.make('decodebin', 'demuxer') videoconv = Gst.ElementFactory.make('videoconvert', 'converter') videosink = Gst.ElementFactory.make('xvimagesink', 'video-output') demuxer.connect('pad-added', self.demuxer_callback, videoconv) for ele in [source, demuxer, videoconv, videosink]: self.player.add(ele) source.link(demuxer) videoconv.link(videosink) bus = self.player.get_bus() bus.add_signal_watch() bus.connect('message', self.on_message) def start_stop(self, w): if self.button.get_label() == 'Start': filepath = self.entry.get_text().strip() if os.path.isfile(filepath): filepath = os.path.realpath(filepath) self.button.set_label('Stop') self.player.get_by_name('file-source').set_property('location', filepath) self.player.set_state(Gst.State.PLAYING) self.play_thread_id = _thread.start_new_thread(self.play_thread, ()) else: self.play_thread_id = None self.player.set_state(Gst.State.NULL) self.button.set_label('Start') self.time_label.set_text('00:00 / 00:00') def play_thread(self): play_thread_id = self.play_thread_id Gdk.threads_enter() self.time_label.set_text('00:00 / 00:00') Gdk.threads_leave() print(play_thread_id) print(self.play_thread_id) while play_thread_id == self.play_thread_id: time.sleep(0.2) dur_int = self.player.query_duration(Gst.Format.TIME)[1] if dur_int == -1: continue dur_str = self.convert_ns(dur_int) Gdk.threads_enter() self.time_label.set_text('00:00 / ' + dur_str) Gdk.threads_leave() break time.sleep(0.2) while play_thread_id == self.play_thread_id: pos_int = self.player.query_position(Gst.Format.TIME)[1] pos_str = self.convert_ns(pos_int) if play_thread_id == self.play_thread_id: Gdk.threads_enter() self.time_label.set_text(pos_str + ' / ' + dur_str) Gdk.threads_leave() time.sleep(1) def on_message(self, bus, message): t = message.type if t == Gst.MessageType.EOS: self.player.seek_simple(Gst.Format.TIME, Gst.SeekFlags.FLUSH, 0000000000) elif t == Gst.MessageType.ERROR: err, debug = message.parse_error() print ('Error: %s' % err, debug) self.play_thread_id = None self.player.set_state(Gst.State.NULL) self.button.set_label('Start') self.time_label.set_text('00:00 / 00:00') def demuxer_callback(self, demuxer, pad, dst): caps = Gst.Pad.get_current_caps(pad) structure_name = caps.to_string() if structure_name.startswith('video'): videorate_pad = dst.get_static_pad('sink') pad.link(videorate_pad) def rewind_callback(self, w): rc, pos_int = self.player.query_position(Gst.Format.TIME) seek_ns = pos_int - 10 * 1000000000 if seek_ns < 0: seek_ns = 0 print (’Backward: %d ns -> %d ns’ % (pos_int, seek_ns)) self.player.seek_simple(Gst.Format.TIME, Gst.SeekFlags.FLUSH, seek_ns) def forward_callback(self, w): rc, pos_int = self.player.query_position(Gst.Format.TIME) seek_ns = pos_int + 10 * 1000000000 print (’Forward: %d ns -> %d ns’ % (pos_int, seek_ns)) self.player.seek_simple(Gst.Format.TIME, Gst.SeekFlags.FLUSH, seek_ns) def convert_ns(self, t): s,ns = divmod(t, 1000000000) m,s = divmod(s, 60) if m < 60: return '%02i:%02i' %(m,s) else: h,m = divmod(m, 60) return '%i:%02i:%02i' %(h,m,s)GObject.threads_init()Gst.init(None)GTK_Main()Gtk.main()

總結

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