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• Open cv.VideoCapture(index) - ffmpeg list camera names - How to match ?

  15 novembre 2024, par Chris P

      def fetch_camera_input_settings(self):
        try:
            self.database_functions = database_functions

            self.camera_input_device_name = database_functions.read_setting("camera_input_device_name")["value"]
            self.camera_input_device_number = int(self.database_functions.read_setting("camera_input_device_number")["value"])

            self.camera_input_devices = [[0,-1,"Καμία συσκευή κάμερας"]]
            self.available_cameras = [{"device_index":-1,"device_name":"Καμία συσκευή κάμερας"}]

            # FFmpeg command to list video capture devices on Windows
            cmd = ["ffmpeg", "-list_devices", "true", "-f", "dshow", "-i", "dummy"]
            result = subprocess.run(cmd, stderr=subprocess.PIPE, stdout=subprocess.PIPE, text=True)
            output = result.stderr  # FFmpeg sends device listing to stderr

            # Updated regular expression to capture both video and audio devices
            device_pattern = re.compile(r'\[dshow @ .+?\] "(.*?)" \(video\)')
            cameras = device_pattern.findall(output)
            counter = 0
            for camera in cameras:
                counter += 1
                self.camera_input_devices.append([counter,counter-1,camera])
                self.available_cameras.append({"device_index": counter-1, "device_name": camera})

            self.to_emitter.send({"type":"available_devices","devices":self.camera_input_devices,"device_index":self.camera_input_device_number})
        except:
            error_message = traceback.format_exc()
            self.to_emitter.send({"type":"error","error_message":error_message})



  


  How to match ffmpeg camera device names output with cv2.VideoCapture which wants camera index as input ?

  


• Low FPS output using ffmpeg and a raspi camera

  23 novembre 2019, par Newe

  I am building a surveillance camera for a school project, which is based on a raspberry pi and a infrared raspberry Pi camera.

  I am capturing the camera’s video stream and outputting it as an HLS stream directly from ffmpeg. However, the resulting video is really low fps ( 5 at max)

  Strangely, raspivid manages to ouput a 60fps 720p stream without any problem, but when put through ffmpeg for streaming, the video is cropped in half and i cannot get it to show up entirely.

  Here is the ffmpeg command i use :

  #!/bin/bash
  
  ffmpeg -v verbose \
  
  -re \
  
  -i /dev/video0 \
  
  -c:v libx264 \
  
  -an \
  
  -f hls \
  
  -g 10  \
  
  -sc_threshold 0 \
  
  -hls_time 1 \
  
  -hls_list_size 4 \
  
  -hls_delete_threshold 1 \
  
  -hls_flags delete_segments \
  
  -hls_start_number_source datetime \
  
  -hls_wrap 15 \
  
  -preset superfast \
  
  -start_number 1 \
  
  /home/pi/serv/assets/stream.m3u8

  And the resulting log output (notice the fps)

  

  Here is the command using raspivid that i tested, based on a blog post i read :

  raspivid -n \
  
  -t 0 \
  
  -w 960 \
  
  -h 540 \
  
  -fps 25 \
  
  -o - | ffmpeg \
  
  -v verbose \
  
  -i - \
  
  -vcodec copy \
  
  -an \
  
  -f hls \
  
  -g 10 \
  
  -sc_threshold 0 \
  
  -hls_time 1 \
  
  -hls_list_size 4 \
  
  -hls_delete_threshold 1 \
  
  -hls_flags delete_segments \
  
  -hls_start_number_source datetime \
  
  -hls_wrap 15 \
  
  -preset superfast \
  
  -start_number 1 \
  
  /home/pi/serv/assets/stream.m3u8

  I am not a ffmpeg expert and am open to any suggestions that would help improve the stream’s quality and stability :)

• How to decode in C a stream from this noname almost-UVC grayscale camera

  18 janvier 2019, par scriptfoo

  Edit : I found the cause. The stream always begins with something which is not a JPEG. Only after it there is a normal MJPEG stream. Interestingly, not all of the small examples of using V4L2/MJPEG decoders can divide what the camera produces properly into frames. Something called capturev4l2.c is a rare example of doing it properly. Possibly there is some detail, which decides if the camera’s bugginess is worked around or not.

  I have a noname almost-UVC-compliant camera (it fails several compatibility tests). This is a relatively cheap global shutter camera, and thus I would like to use it instead of something properly documented. It outputs what is reported (and properly played) by mplayer as

  Opening video decoder: [ffmpeg] FFmpeg's libavcodec codec family
  
  libavcodec version 57.107.100 (external)
  
  Selected video codec: [ffmjpeg] vfm: ffmpeg (FFmpeg MJPEG)

  ffprobe shows the following :

  [mjpeg @ 0x55c086dcc080] Format mjpeg detected only with low score of 25, misdetection possible!
  
  Input #0, mjpeg, from '/home/sc/Desktop/a.raw':
  
    Duration: N/A, bitrate: N/A
  
      Stream #0:0: Video: mjpeg, yuvj422p(pc, bt470bg/unknown/unknown), 640x480, 25 tbr, 1200k tbn, 25 tbc

  But as opposed to mplayer, it is unable to play it.

  I tried decode_jpeg_raw from mjpegtools, it complains about the header, which seems to change with each captured stream. So does not look like an unwrapped stream of JPEG images.

  I thus tried 0_hello_world.c from libavcodec/libavformat, but its stops at avformat_open_input() with an error Invalid data found when processing input. A 100-frame sample file is sitting here a.raw. Do you have any idea how to determine a method of decoding it in C into anything plain bitmap ?

  The file is grayscale, does not begin with a constant value, guvcview and mplayer are the only players I know, which can decode it without artifacts...