python gstreamer实现视频快进/快退/循环播放功能

gstreamer到底是个啥？

gstreamer 是一个 基于pipeline的多媒体框架，基于gobject，以c语言写成。

应用gstreamer这个这个多媒体框架，你可以写出任意一种流媒体的应用来如：meidaplayer、音视频编辑器、voip、流媒体服务器、音视频编码等等。

关于视频快进/快退/循环播放的知识总结:

1.本地视频时长获取:

gst.pad.query_duration官方函数介绍:

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 requested

returns 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为播放本地视频的管道,query_duration()函数返回一个元组,元组的形式为[ture,duration:******]，******为以ns为单位的视频时长。

2.视频播放当前位置获取：

gst.pad.query_position官方函数介绍：

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 requested

returns 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.

使用方法与时长获取函数query_duration()相同。

3.播放跳转函数：

gst.element.seek_simple官方函数介绍：

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 on
format ( gst.format ) –a gst.format to execute the seek in, such as gst.format.time
seek_flags ( gst.seekflags ) –seek options; playback applications will usually want to use gst_seek_flag_flush | gst_seek_flag_key_unit here
seek_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.

函数使用样例：

pipeline.seek_simple(gst.format.time, gst.seekflags.flush, time)

其中time的单位为nanoseconds。

有视频快进/快退/循环播放功能的小播放器.

import os, _thread, time
import gi
gi.require_version("gst", "1.0")
gi.require_version('gtk', '3.0')
from gi.repository import gst, gobject, gtk, gdk
class 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()

总结

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