video.py

#!/usr/bin/env python
"""
BlueRov video capture class
"""

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
        latest_frame (np.ndarray): Latest retrieved video frame
    """

    def __init__(self, port=5600):
        """Summary

        Args:
            port (int, optional): UDP port
        """

        Gst.init(None)

        self.port = port
        self.latest_frame = self._new_frame = None

        # [Software component diagram](https://www.ardusub.com/software/components.html)
        # UDP video stream (:5600)
        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"
        )
        # 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_structure = sample.get_caps().get_structure(0)
        array = np.ndarray(
            (caps_structure.get_value("height"), caps_structure.get_value("width"), 3),
            buffer=buf.extract_dup(0, buf.get_size()),
            dtype=np.uint8,
        )
        return array

    def frame(self):
        """Get Frame

        Returns:
            np.ndarray: latest retrieved image frame
        """
        if self.frame_available:
            self.latest_frame = self._new_frame
            # reset to indicate latest frame has been 'consumed'
            self._new_frame = None
        return self.latest_frame

    def frame_available(self):
        """Check if a new frame is available

        Returns:
            bool: true if a new frame is available
        """
        return self._new_frame is not None

    def run(self):
        """Get frame to update _new_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")
        self._new_frame = self.gst_to_opencv(sample)

        return Gst.FlowReturn.OK


if __name__ == "__main__":
    # Create the video object
    # Add port= if is necessary to use a different one
    video = Video()

    print("Initialising stream...")
    waited = 0
    while not video.frame_available():
        waited += 1
        print("\r  Frame not available (x{})".format(waited), end="")
        cv2.waitKey(30)
    print('\nSuccess!\nStarting streaming - press "q" to quit.')

    while True:
        # Wait for the next frame to become available
        if video.frame_available():
            # Only retrieve and display a frame if it's new
            frame = video.frame()
            cv2.imshow("frame", frame)
        # Allow frame to display, and check if user wants to quit
        if cv2.waitKey(1) & 0xFF == ord("q"):
            break