我正在尝试使用Python捕获并显示网络视频流。已使用以下命令在我的笔记本电脑上创建了流：
gst-launch-1.0 v4l2src ! videorate ! video/x-raw,framerate=2/1,width=640,height=480 ! x264enc pass=qual quantizer=20 tune=zerolatency ! rtph264pay config-interval=10 pt=96 ! udpsink host=127.0.0.1 port=5000
它需要网络摄像头输入并通过UDP端口进行流式传输。我可以使用以下命令捕获流并显示它：
gst-launch-1.0 udpsrc port=5000 ! "application/x-rtp, payload=127" ! rtph264depay ! avdec_h264 ! xvimagesink sync=false
现在我正在尝试使用Python脚本执行相同的操作（捕获），但不缺。这是我的代码：
import gi
gi.require_version('Gst', '1.0')
from gi.repository import Gst
udpPipe = Gst.pipeline("player")
source = Gst.ElementFactory.make('udpsrc', None)
source.set_property("port", 5000)
source.set_property("host", "127.0.0.1")
rdepay = Gst.ElementFactory.make('rtph264depay', 'rdepay')
vdecode = Gst.ElementFactory.make('avdec_h264', 'vdecode')
sink = Gst.ElementFactory.make('xvimagesink', None)
udpPipe.add(source, rdepay, vdecode, sink)
gst.element_link_many(source, rdepay, vdecode, sink)
udpPipe.set_state(gst.STATE_PLAYING)
我得到的错误是：
/usr/lib/python2.7/dist-packages/gi/overrides/Gst.py:56: Warning: /build/glib2.0-prJhLS/glib2.0-2.48.2/./gobject/gsignal.c:1674: parameter 1 of type '<invalid>' for signal "GstBus::sync_message" is not a value type
Gst.Bin.__init__(self, name=name)
/usr/lib/python2.7/dist-packages/gi/overrides/Gst.py:56: Warning: /build/glib2.0-prJhLS/glib2.0-2.48.2/./gobject/gsignal.c:1674: parameter 1 of type '<invalid>' for signal "GstBus::message" is not a value type
Gst.Bin.__init__(self, name=name)
Traceback (most recent call last):
File "getUdp.py", line 13, in <module>
source = Gst.ElementFactory.make('udpsrc', None)
File "/usr/lib/python2.7/dist-packages/gi/overrides/Gst.py", line 217, in make
return Gst.ElementFactory.make(factory_name, instance_name)
TypeError: unbound method fake_method() must be called with ElementFactory instance as first argument (got str instance instead)
有什么想法吗？ ： - （
答案 0 :(得分：2)
今天我在Debian 9.3（延伸）上也遇到了同样的错误。 明确调用Gst.init可以解决问题。
以下代码在我的系统上弹出了一个xvimagesink窗口，同时包含python 2.7和3.5。
#!/usr/bin/python
import sys
import gi
gi.require_version('GLib', '2.0')
gi.require_version('Gst', '1.0')
from gi.repository import GLib, Gst
Gst.init(sys.argv)
udpPipe = Gst.Pipeline("player")
source = Gst.ElementFactory.make('udpsrc', None)
source.set_property("port", 5000)
#source.set_property("host", "127.0.0.1")
caps = Gst.caps_from_string("application/x-rtp, payload=127")
source.set_property("caps", caps)
rdepay = Gst.ElementFactory.make('rtph264depay', 'rdepay')
vdecode = Gst.ElementFactory.make('avdec_h264', 'vdecode')
sink = Gst.ElementFactory.make('xvimagesink', None)
sink.set_property("sync", False)
udpPipe.add(source, rdepay, vdecode, sink)
#Gst.element_link_many(source, rdepay, vdecode, sink)
source.link(rdepay)
rdepay.link(vdecode)
vdecode.link(sink)
udpPipe.set_state(Gst.State.PLAYING)
GLib.MainLoop().run()
我认为有必要调用Gst.init并使用PyGObject运行mainloop将gst-launch命令行转换为python脚本。
答案 1 :(得分：0)
您可以按以下方式使用“ mjpeg”流：
gst-launch-1.0 videotestsrc ! videoconvert ! videoscale ! video/x-raw,format=I420,width=800,height=600,framerate=25/1 ! jpegenc ! rtpjpegpay ! udpsink host=127.0.0.1 port=5000
在python3中，您可以像这样获得框架：
#!/usr/bin/env python
import cv2
import gi
import numpy as np
gi.require_version('Gst', '1.0')
from gi.repository import Gst
class Video():
"""BlueRov video capture class constructor
Attributes:
port (int): Video UDP port
video_codec (string): Source h264 parser
video_decode (string): Transform YUV (12bits) to BGR (24bits)
video_pipe (object): GStreamer top-level pipeline
video_sink (object): Gstreamer sink element
video_sink_conf (string): Sink configuration
video_source (string): Udp source ip and port
"""
def __init__(self, port=5000):
"""Summary
Args:
port (int, optional): UDP port
"""
Gst.init(None)
self.port = port
self._frame = None
# [Software component diagram](https://www.ardusub.com/software/components.html)
# UDP video stream (:5000)
self.video_source = 'udpsrc port={}'.format(self.port)
# [Rasp raw image](http://picamera.readthedocs.io/en/release-0.7/recipes2.html#raw-image-capture-yuv-format)
# Cam -> CSI-2 -> H264 Raw (YUV 4-4-4 (12bits) I420)
# self.video_codec = '! application/x-rtp, payload=96 ! rtph264depay ! h264parse ! avdec_h264'
self.video_codec = '! application/x-rtp, payload=26 ! rtpjpegdepay ! jpegdec'
# Python don't have nibble, convert YUV nibbles (4-4-4) to OpenCV standard BGR bytes (8-8-8)
self.video_decode = \
'! decodebin ! videoconvert ! video/x-raw,format=(string)BGR ! videoconvert'
# Create a sink to get data
self.video_sink_conf = \
'! appsink emit-signals=true sync=false max-buffers=2 drop=true'
self.video_pipe = None
self.video_sink = None
self.run()
def start_gst(self, config=None):
""" Start gstreamer pipeline and sink
Pipeline description list e.g:
[
'videotestsrc ! decodebin', \
'! videoconvert ! video/x-raw,format=(string)BGR ! videoconvert',
'! appsink'
]
Args:
config (list, optional): Gstreamer pileline description list
"""
if not config:
config = \
[
'videotestsrc ! decodebin',
'! videoconvert ! video/x-raw,format=(string)BGR ! videoconvert',
'! appsink'
]
command = ' '.join(config)
self.video_pipe = Gst.parse_launch(command)
self.video_pipe.set_state(Gst.State.PLAYING)
self.video_sink = self.video_pipe.get_by_name('appsink0')
@staticmethod
def gst_to_opencv(sample):
"""Transform byte array into np array
Args:
sample (TYPE): Description
Returns:
TYPE: Description
"""
buf = sample.get_buffer()
caps = sample.get_caps()
array = np.ndarray(
(
caps.get_structure(0).get_value('height'),
caps.get_structure(0).get_value('width'),
3
),
buffer=buf.extract_dup(0, buf.get_size()), dtype=np.uint8)
return array
def frame(self):
""" Get Frame
Returns:
iterable: bool and image frame, cap.read() output
"""
return self._frame
def frame_available(self):
"""Check if frame is available
Returns:
bool: true if frame is available
"""
return type(self._frame) != type(None)
def run(self):
""" Get frame to update _frame
"""
self.start_gst(
[
self.video_source,
self.video_codec,
self.video_decode,
self.video_sink_conf
])
self.video_sink.connect('new-sample', self.callback)
def callback(self, sink):
sample = sink.emit('pull-sample')
new_frame = self.gst_to_opencv(sample)
self._frame = new_frame
return Gst.FlowReturn.OK
if __name__ == '__main__':
# Create the video object
# Add port= if is necessary to use a different one
video = Video(port=5000)
while True:
# Wait for the next frame
if not video.frame_available():
continue
frame = video.frame()
cv2.imshow('frame', frame)
if cv2.waitKey(1) & 0xFF == ord('q'):
break
REF
1：http://www.einarsundgren.se/gstreamer-basic-real-time-streaming-tutorial/
2：https://gist.github.com/patrickelectric/443645bb0fd6e71b34c504d20d475d5a