video_stream.py

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import threading
from . protocol import *


class VideoStream(object):
    def __init__(self, drone):
        self.drone = drone
        self.log = drone.log
        self.cond = threading.Condition()
        self.queue = []
        self.closed = False
        self.prev_video_data = None
        self.wait_first_packet_in_frame = True
        self.ignore_packets = 0
        self.name = 'VideoStream'
        drone.subscribe(drone.EVENT_CONNECTED, self.__handle_event)
        drone.subscribe(drone.EVENT_DISCONNECTED, self.__handle_event)
        drone.subscribe(drone.EVENT_VIDEO_DATA, self.__handle_event)

    def read(self, size):
        self.cond.acquire()
        try:
            if len(self.queue) == 0 and not self.closed:
                self.cond.wait(5.0)
            data = bytes()
            while 0 < len(self.queue) and len(data) + len(self.queue[0]) < size:
                data = data + self.queue[0]
                del self.queue[0]
        finally:
            self.cond.release()
        # returning data of zero length indicates end of stream
        self.log.debug('%s.read(size=%d) = %d' % (self.name, size, len(data)))
        return data

    def seek(self, offset, whence):
        self.log.info('%s.seek(%d, %d)' % (str(self.name), offset, whence))
        return -1

    def __handle_event(self, event, sender, data):
        if event is self.drone.EVENT_CONNECTED:
            self.log.info('%s.handle_event(CONNECTED)' % (self.name))
        elif event is self.drone.EVENT_DISCONNECTED:
            self.log.info('%s.handle_event(DISCONNECTED)' % (self.name))
            self.cond.acquire()
            self.queue = []
            self.closed = True
            self.cond.notifyAll()
            self.cond.release()
        elif event is self.drone.EVENT_VIDEO_DATA:
            self.log.debug('%s.handle_event(VIDEO_DATA, size=%d)' % (self.name, len(data)))
            video_data = VideoData(data)
            if 0 < video_data.gap(self.prev_video_data):
                self.wait_first_packet_in_frame = True
                
            self.prev_video_data = video_data
            if self.wait_first_packet_in_frame and byte(data[1]) != 0:
                self.ignore_packets += 1
                return
            if self.wait_first_packet_in_frame:
                self.log.debug('%s.handle_event(VIDEO_DATA): ignore %d packets' %
                               (self.name, self.ignore_packets))
            self.ignore_packets = 0
            self.wait_first_packet_in_frame = False

            self.cond.acquire()
            self.queue.append(data[2:])
            self.cond.notifyAll()
            self.cond.release()