Record frames to video about flask-video-streaming

[miguelgrinberg]

There is a complete implementation of a video file writer for Python in this article: https://www.learnopencv.com/read-write-and-display-a-video-using-opencv-cpp-python/.

[robsmall]

Thanks for the quick response and share! I was hoping to avoid needing to use openCV as well as picamera to generate the data to write to the file so I could use the same stream that is sent over the network. I was looking to achieve this by using a custom StreamingOutput from the picamera's recording like so:

class StreamingOutput(object):
    def __init__(self):
        self.frame = None
        self.buffer = io.BytesIO()

    def write(self, buf):
        if buf.startswith(b'\xff\xd8'):
            # New frame, copy the existing buffer's content and notify all
            # clients it's available
            self.buffer.truncate()
            self.frame = self.buffer.getvalue()
            self.buffer.seek(0)
        return self.buffer.write(buf)

    def flush(self):
        print "\n\nflush!!!!\n\n"
        try:
            fourcc = cv2.cv.CV_FOURCC(*'MJPG')
            out = cv2.VideoWriter("output.avi", fourcc, 40.0, (1640, 922))

            arr = np.fromstring(self.buffer.getvalue(), dtype=np.uint8)
            out.write(arr)

            # Release everything if job is finished
            out.release()
            cv2.destroyAllWindows()
        except Exception as e:
            print e


class Camera(BaseCamera):
    camera = None
    output = None

    @staticmethod
    def start_recording():
        """ Start recording from the camera object. """
        Camera.camera.start_recording(Camera.output, format='mjpeg')

    @staticmethod
    def stop_recording():
        """ Stop the Camera object from recording. """
        Camera.camera.stop_recording()

    @staticmethod
    def frames():
        with picamera.PiCamera(
                sensor_mode=5, resolution="1640x922", framerate=40) as camera:
            Camera.camera = camera
            Camera.output = StreamingOutput()

            Camera.start_recording()
            
            while True:
                frame = Camera.output.frame
                yield frame

The issue is when I open the output avi file (output.avi), it is empty. I also tried writing the frames themselves but to no avail. Curious if you have any pointers here.

[miguelgrinberg]

The code that you are using is not written by me, it is actually based on code that I wrote, but was modified in a way that I don't fully understand. You now took that code and modified it even more, so I can't really tell you for sure what's wrong. What seems wrong to me though, is that the flush() function is opening the video file. My guess is that flush() is called several times during the recording, and each time it is called, you are creating a new video file, overwriting anything you may have written to it before that.

[robsmall]

Thanks for the insight! flush() is called at the end of the output (according to the picamera docs) from the picamera. I was using this to PoC writing the output to a file by terminating the feed and looking at the file after recording for a while. Unfortunately, in reading up some more it looks like there are quite a few issues here.

Sorry for asking about modified broken code, I wanted to flag this as a question not an issue to see if you had any insight into writing the output from a stream to a file but in hindsight this is more of a question about writing picamera output to a file on a pi, not about the code in this repo. Will close.

[robsmall]

Well... That was very broken. The issue was that I wasn't thinking clearly and missed the fact that I was truncating the buffer so it was only writing a single frame. The solution is to write out each frame and then release the buffer at the end:

class StreamingOutput(object):
    def __init__(self):
        self.frame = None
        self.buffer = io.BytesIO()

        four_cc = cv2.cv.CV_FOURCC(*'MJPG')
        now = datetime.datetime.now()
        self.out = cv2.VideoWriter(
            "output_{}.avi".format(now.strftime("%Y-%m-%d_%H:%M:%S")),
            four_cc,
            30,
            (1640, 922))

    def write(self, buf):
        if buf.startswith(b'\xff\xd8'):
            # New frame, copy the existing buffer's content and notify all
            # clients it's available
            self.buffer.truncate()
            self.frame = self.buffer.getvalue()
            self.buffer.seek(0)

            arr = cv2.imdecode(np.fromstring(buf, dtype=np.uint8), 1)
            self.out.write(arr)

            return self.buffer.write(buf)

    def flush(self):
        # Release everything since the job is finished
        self.out.release()
        cv2.destroyAllWindows()

[LMJayasundara]

Hello

Is there any way to do this