Recherche avancée

Sur d’autres sites (16555)

• draw a rectangle on YUV420p frame with python opencv

  18 janvier 2021, par user3705497

  I have a python script sandwiched between ffmpeg input and output commands
logically looks like the following :

  


  ffmpeg -i webcam -vf format=yuv420p -f rawvideo - | python below.py | ffmpeg -f rawvideo -video_size 640x480 -i - -f sometype some_output 


  


  Below is the python script snippet :

  


  import cv2 as cv
import sys
import subprocess as sp
import numpy as np

if sys.platform == "win32":
    import os, msvcrt
    msvcrt.setmode(sys.stdout.fileno(), os.O_BINARY)

width = 640
height = 480

FFMPEG_BIN = 'ffmpeg'
command = [ FFMPEG_BIN,
            '-re',
            '-f', 'dshow',
            '-rtbufsize', '200M',
            '-i', 'video=USB2.0 VGA UVC WebCam',
            '-vf', 'format=yuv420p',
            '-f', 'rawvideo', '-']
pipe = sp.Popen(command, stdout = sp.PIPE, bufsize=10**8) 

while True:
    raw_image = pipe.stdout.read(width*height*3)
    frame = np.frombuffer(raw_image, dtype='uint8')

    frame = frame.reshape((height,width,3)) 

    # cv.rectangle(frame, (xmin, ymin), (xmax, ymax), color=(0, 255, 0), thickness=1)

    sys.stdout.buffer.write( frame.tostring() )


  


  I want to draw a rectangle on the YUV frame. I can't seem to get the right color (should be green - (0, 255, 0))

  


  My understanding, so far, is to break down the frame into 3 pieces Y, U, V and rejoin them. Not sure if this is correct and Which layer should I call cv.rectangle on ?

  


• Pipe video frames from ffmpeg to canvas without loading the entire video into memory

  1er janvier 2024, par Aviato

  I am working on a project that involves frame manipulation and I decided to choose node canvas API for that. I used to work with OpenCV Python and there was a cv2.VideoCapture class that takes a video as input and prepares to read the frames of the video and we can loop through the frames one at a time without having to load all the frames at once in memory.
Now I tried a lot of ways to replicate the same using ffmpeg, i.e. trying to load frames from a video in an ordered, but "on-demand," fashion.

  


  I tried using ffmpeg as a child process to process frames and standout the frames.

  


  const spawnProcess = require('child_process').spawn,
    ffmpeg = spawnProcess('ffmpeg', [
        '-i', 'test.mp4',
        '-vcodec', 'png',
        '-f', 'rawvideo',
        '-s', '1920*1080', // size of one frame
        'pipe:1'
    ]);
ffmpeg.stdout.on('data', (data) => {
    try {
        // console.log(tf.node.decodeImage(data).shape)
        console.log(`${++i} frames read`)
        //context.drawImage(data, 0, 0, width, height)
        
        
    } catch(e) {
        console.log(e)
    } 
})


  


  The value in the console shows something around 4000 + console logs, but the video only had 150 frames, after much investigating and console logging the data, I found that was buffer data, and it's not processing it for each frame. The on-data function returns the buffer data in an unstructured way
I want to read frames from a video and process each one at a time in memory, I don't want to hold all the frames at once in memory or in the filesystem.

  


  

  


  I also want to pipe the frames in a format that could be rendered on top of a canvas using drawImage

  


• How to encode a series of .dpx files using X264

  4 juin 2015, par user3759710

  I am complete newbie to video encoding. I am trying to encode a series of .dpx files into one single encoded video O/P file in any of the following format. ( .mp4,.avi,.h264,.mkv etc)

  I have tried 2 different approaches. The first one works and the second one does not.
  I would like to know the difference between the two. Any help / input would be much appreciated.

  1) using FFMPEG along with x264 library and it works well. I am able to produce desired output

  ffmpeg -start_number 0 -i frame%4d.dpx -pix_fmt yuv420p -c:v libx264 -crf 28 
  
  -profile:v baseline fromdpx.h264

  2) I first try to concatenate all the dpx files into a single file using concate protocol in ffmpeg and then use x264 to encode the concatenated file.
  Here I see that the size of the concatenated file is the sum of all the files concatenated. But when I use x264 command to encode the concatenated file, I get a green screen (basically not the desired output) .

  ffmpeg -i "concat:frame0.dpx|frame01.dpx|frame2.dpx etc" -c copy output.dpx

  then

  x264 --crf 28 --profile baseline -o encoded.mp4 --input-res 1920x1080 --demuxer raw 
  
  output.dpx

  I also tried to encoded the concatenated file using ffmpeg as follows

  ffmpeg -i output.dpx -pix_fmt yuv420p -c:v libx264 -crf 28 -profile:v baseline fromdpx.h264

  This also gives me a blank video.

  Could someone please point out to me what is going on here ? Why does the first method work and the second does not ?

  Thank you.