Python + GStreamer：将视频缩放到窗口

Question

我在将GStreamer的视频输出重新缩放到显示视频的窗口尺寸（保留视频的纵横比）时遇到了一些麻烦。问题是我首先需要预先录制视频，以便能够通过检索协商的上限来确定其尺寸，然后计算出需要显示的尺寸以适应窗口。一旦我预卷了视频并获得了尺寸上限，我无法再更改视频的尺寸。设置新的大小写仍然会导致视频以原始大小输出。我必须做些什么来解决这个问题？

只是要完成。在当前的实现中，我无法渲染到可轻松解决此问题的OpenGL纹理，因为您可以将输出渲染到纹理并将其缩放以适合屏幕。我必须在pygame表面上绘制输出，它需要具有正确的尺寸。 pygame确实提供了扩展其表面的功能，但我认为这样的实现（比如我现在）比直接从GStreamer直接检索正确大小的帧要慢（我是吧？）

这是我的代码和显示视频（我省略了主循环的东西）：

def calcScaledRes(self, screen_res, image_res): 
    """Calculate image size so it fits the screen 
    Args 
     screen_res (tuple) - Display window size/Resolution 
     image_res (tuple) - Image width and height 

    Returns 
     tuple - width and height of image scaled to window/screen 
    """ 
    rs = screen_res[0]/float(screen_res[1]) 
    ri = image_res[0]/float(image_res[1]) 

    if rs > ri: 
     return (int(image_res[0] * screen_res[1]/image_res[1]), screen_res[1]) 
    else: 
     return (screen_res[0], int(image_res[1]*screen_res[0]/image_res[0])) 

def load(self, vfile): 
    """ 
    Loads a videofile and makes it ready for playback 

    Arguments: 
    vfile -- the uri to the file to be played 
    """ 
    # Info required for color space conversion (YUV->RGB) 
    # masks are necessary for correct display on unix systems 
    _VIDEO_CAPS = ','.join([ 
     'video/x-raw-rgb', 
     'red_mask=(int)0xff0000', 
     'green_mask=(int)0x00ff00', 
     'blue_mask=(int)0x0000ff' 
    ]) 

    self.caps = gst.Caps(_VIDEO_CAPS) 

    # Create videoplayer and load URI 
    self.player = gst.element_factory_make("playbin2", "player")   
    self.player.set_property("uri", vfile) 

    # Enable deinterlacing of video if necessary 
    self.player.props.flags |= (1 << 9)  

    # Reroute frame output to Python 
    self._videosink = gst.element_factory_make('appsink', 'videosink')  
    self._videosink.set_property('caps', self.caps) 
    self._videosink.set_property('async', True) 
    self._videosink.set_property('drop', True) 
    self._videosink.set_property('emit-signals', True) 
    self._videosink.connect('new-buffer', self.__handle_videoframe)  
    self.player.set_property('video-sink', self._videosink) 

    # Preroll movie to get dimension data 
    self.player.set_state(gst.STATE_PAUSED) 

    # If movie is loaded correctly, info about the clip should be available 
    if self.player.get_state(gst.CLOCK_TIME_NONE)[0] == gst.STATE_CHANGE_SUCCESS: 
     pads = self._videosink.pads()   
     for pad in pads:    
      caps = pad.get_negotiated_caps()[0] 
      self.vidsize = caps['width'], caps['height'] 
     else: 
      raise exceptions.runtime_error("Failed to retrieve video size") 

# Calculate size of video when fit to screen 
    self.scaledVideoSize = self.calcScaledRes((self.screen_width,self.screen_height), self.vidsize) 
# Calculate the top left corner of the video (to later center it vertically on screen) 
    self.vidPos = ((self.screen_width - self.scaledVideoSize [0])/2, (self.screen_height - self.scaledVideoSize [1])/2) 

    # Add width and height info to video caps and reload caps 
    _VIDEO_CAPS += ", width={0}, heigh={1}".format(self.scaledVideoSize[0], self.scaledVideoSize[1]) 
    self.caps = gst.Caps(_VIDEO_CAPS) 
    self._videosink.set_property('caps', self.caps) #??? not working, video still displayed in original size 

def __handle_videoframe(self, appsink): 
    """ 
    Callback method for handling a video frame 

    Arguments: 
    appsink -- the sink to which gst supplies the frame (not used) 
    """  
    buffer = self._videosink.emit('pull-buffer')   

    img = pygame.image.frombuffer(buffer.data, self.vidsize, "RGB") 

    # Upscale image to new surfuace if presented fullscreen 
    # Create the surface if it doesn't exist yet and keep rendering to this surface 
    # for future frames (should be faster) 

    if not hasattr(self,"destSurf"):     
     self.destSurf = pygame.transform.scale(img, self.destsize) 
    else: 
     pygame.transform.scale(img, self.destsize, self.destSurf) 
    self.screen.blit(self.destSurf, self.vidPos) 

    # Swap the buffers 
    pygame.display.flip() 

    # Increase frame counter 
    self.frameNo += 1 

Answer 1

我敢肯定，你的问题是（有它是因为你问的这个问题很长一段时间），你从来没有迷上了公交车注意发出的消息。
的代码，这通常是这样的：

def some_function(self): 
    #code defining Gplayer (the pipeline) 
    # 
    # here 
     Gplayer.set_property('flags', self.GST_VIDEO|self.GST_AUDIO|self.GST_TEXT|self.GST_SOFT_VOLUME|self.GST_DEINTERLACE) 
    # more code 
    # 
    # finally 
     # Create the bus to listen for messages 
     bus = Gplayer.get_bus() 
     bus.add_signal_watch() 
     bus.enable_sync_message_emission() 
     bus.connect('message', self.OnBusMessage) 
     bus.connect('sync-message::element', self.OnSyncMessage) 
# Listen for gstreamer bus messages 
    def OnBusMessage(self, bus, message): 
     t = message.type 
     if t == Gst.MessageType.ERROR: 
      pass 
     elif t == Gst.MessageType.EOS: 
      print ("End of Audio") 
     return True 

    def OnSyncMessage(self, bus, msg): 
     if msg.get_structure() is None: 
      return True 
     if message_name == 'prepare-window-handle': 
      imagesink = msg.src 
      imagesink.set_property('force-aspect-ratio', True) 
      imagesink.set_window_handle(self.panel1.GetHandle())  

您的问题的关键位是建立一个回调的同步消息，并在回拨，物业force-aspect-ratio设置为True。
此属性可确保视频适合其始终显示的窗口。

请注意self.panel1.GetHandle（）函数命名您要在其中显示视频的面板。

我明白你会继续前进，但希望这将有助于其他人通过档案拖网。