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• Convert RGB Video to Gray Scale video for file size reduction

  28 janvier 2020, par flamelite

  I am creating Color Video(RGB) using OpenCV in my application and generated video file needs to be uploaded to server. Color video file size is large enough to create bottleneck while uploading to server in the current bandwidth available. So, i tried to reduce the file size by converting it to grayscale video in the opencv.
  Please find below the OpenCV implementation of my current work :

  cap = cv2.VideoCapture(RGB_video_filepath)
  
      fps = cap.get(cv2.CAP_PROP_FPS)
  
      print("Input Video FPS: ".format(fps))
  
      outputfilepath = "gray_video_output.avi"
  
  
  
      mjpg_forcc = cv2.VideoWriter_fourcc('M', 'J', 'P', 'G')
  
      divx_forcc = cv2.VideoWriter_fourcc(*'DIVX')
  
      xvid_forcc = cv2.VideoWriter_fourcc(*'XVID')
  
      fmpp4_codec = cv2.VideoWriter_fourcc('F','M','P','4')
  
      mp4v_codec = cv2.VideoWriter_fourcc(*'MP4V')
  
      vid_writer = cv2.VideoWriter(outputfilepath, mjpg_codec, 2, (640, 480), 0)
  
  
  
      while cv2.waitKey(1) < 0:
  
          # get frame from the video
  
          hasFrame, frame = cap.read()
  
  
  
  
  
          # Stop the program if reached end of video
  
          if not hasFrame:
  
              print("Done processing !!!")
  
              print("Output file is stored as ", outputfilepath)
  
              break
  
  
  
          gray_frame = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)
  
          vid_writer.write(gray_frame)
  
          print("Frame shape: {} {}".format(frame_count, frame.shape))
  
          cv2.imshow("Camera frame", frame)
  
          cv2.waitKey(1)
  
  
  
      print("Total frames: {}".format(frame_count))
  
      vid_writer.release()
  
      cap.release()

  Using above workflow, i created the GRAY scale video, but i found that video file sizes are almost same (RGB video file size : 25 MB, Gray scale video size : 23 MB).

  After digging into OpenCV, i found that OpenCV copies the grayscale(single channel) frame 3 times and writes into video as 3 channel although OpenCV uses FFMPEG for video file writing on Linux based OS.

  I tried to convert the same RGB video file to Grayscale video file using FFMPEG as below :

  ffmpeg -i inputvideofile -vf hue=s=0 outputvideofile

  Here, i kept the Hue and saturation channel to be empty and surprisingly RGB video file(25 MB) gets converted to gray scale with file size reduced to 6 MB.

  **I am curious to know if we can achieve the video file size reduction by converting RGB to Gray scale using OpenCV on the fly ? **

  Any help/update is appreciated.
  Thanks !!

• How to merge webm video with mp4 video with transperency ?

  30 novembre 2017, par kostya572

  I have 1080p webm video and 500x300 mp4 video. How could I place muted mp4 video on top-center position of webm video with transparency ? The output file format needed ".webm". Here what similar code I found, but it uses two mp4 videos and second video scales full width on front of first one :

  ffmpeg \
       -i in1.mp4 -i in2.mp4 \
       -filter_complex " \
           [0:v]setpts=PTS-STARTPTS, scale=480x360[top]; \
           [1:v]setpts=PTS-STARTPTS, scale=480x360, \
                format=yuva420p,colorchannelmixer=aa=0.5[bottom]; \
           [top][bottom]overlay=shortest=1" \
       -vcodec libx264 out.mp4

  Output log :
  

• ffmpeg remove multiple segments from a video rotate and crop video

  2 novembre 2017, par 1234567

  ffmpeg remove multiple segments from a video rotate and crop video

  I have a video of 2 min 25 seconds , i want to remove part from 10 second to 16 second and 20 second to 26 second and rotate video and crop it

  I am trying this command

   "-y", "-i", j,
  
                        "-filter_complex",
  
                          "[0:v]trim=start=10:end=16,setpts=PTS-STARTPTS[a];  " +
  
                                  "[0:v]trim=start=20:end=26,setpts=PTS-STARTPTS[b]; " +
  
                                  "[0:a]atrim=start=10:end=16,asetpts=PTS-STARTPTS[c]; " +
  
                                  "[0:a]atrim=start=20:end=26,asetpts=PTS-STARTPTS[d]; " +
  
                                  "[a][c][b][d]concat=n=2:v=1:a=1[e][f],"+
  
                                  "crop=" + 40 + ":" + 20 + ":" + 100 + ":" + 100,"+
  
                                  "transpose=1", "-map", "'[e]'" ,"-map",
  
                          "'[f]'", "-preset", "ultrafast",out

  what is the correct command to do it