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• when webm extracts aac, the duration is inconsistent

  25 juillet 2019, par Black-Hole

  When I try to extract aac from webm, there will be inconsistencies in duration. aac is ten minutes less. Different webm videos, the gap is not the same.

  webm video is generated by chrome extension chrome.tabCapture.capture

  code :

  chrome.tabCapture.capture({
  
    video: true,
  
    audio: true,
  
    videoConstraints: {
  
      mandatory: {
  
        minWidth: 1920,
  
        minHeight: 1080,
  
        maxWidth: 1920,
  
        maxHeight: 1080,
  
        maxFrameRate: 30,
  
        minFrameRate: 30,
  
      }
  
    }
  
  })

  The above code will return a stream, I will use JS’s MediaRecorder method to process this stream, and finally save it as a webm file.

  code :

  new MediaRecorder(stream, {
  
    audioBitsPerSecond: 128000,
  
    videoBitsPerSecond: 2500000,
  
    mimeType: 'video/webm;codecs=vp9'
  
  })

  If you don’t know the meaning of the above code, it doesn’t matter, I will explain the main information :

  1. width : 1920
  2. height : 1080
  3. FPS : 30
  4. audioBits : 128000
  5. videoBits : 2500000
  6. mimeType : video/webm;codecs=vp9

  I tried a lot of methods, like the following :

  # 1
  
  ffmpeg -i ./source.webm -y -fflags +genpts -max_muxing_queue_size 99999 -r 15 -crf 30 -filter:v crop=750:560:0:0 ./x.mp4
  
  ffmpeg -i ./x.mp4 -y -vn -acodec libfdk_aac -b:a 200k ./x.aac
  
  
  
  # 2
  
  ffmpeg -i ./source.webm -y -vn -acodec libfdk_aac -b:a 200k ./x.aac
  
  
  
  # 3
  
  ffmpeg -i ./source.webm -y -vn -acodec libfdk_aac -b:a 200k -map 0 ./x.aac
  
  
  
  # 4
  
  ffmpeg -i ./source.webm -y -max_muxing_queue_size 99999 -r 15 -crf 30 -filter:v crop=750:560:0:0 ./x.mp4
  
  ffmpeg -i ./source.webm -y -vn -acodec aac -b:a 200k ./x.aac
  
  
  
  # etc.

  But without exception, all failed. I have been plagued by this problem for 4 days.

  webm file download url : https://drive.google.com/file/d/1m4fC1hU-tXFPOZayrYCs-yteSTxw_TaW/view?usp=sharing

• avcodec : Add "sar" alias to "aspect" option of video encoders

  5 mai 2016, par Andrey Utkin

  avcodec : Add "sar" alias to "aspect" option of video encoders
  It is impossible to pass "aspect" parameter to encoder from ffmpeg CLI
  
  because option from lavc/options_table.h is eclipsed by option with same
  
  name in ffmpeg_opt.c, which has different meaning (DAR, not SAR).
  Signed-off-by : Michael Niedermayer <michael@niedermayer.cc>
  

  • [DH] doc/codecs.texi
  • [DH] libavcodec/options_table.h
  • [DH] tests/ref/fate/api-mjpeg-codec-param
  • [DH] tests/ref/fate/api-png-codec-param

• How Do I Get Python To Capture My Screen At The Right Frame Rate

  14 juillet 2024, par John Thesaurus

  I have this python script that is supposed to record my screen, on mac os.

  


  import cv2
import numpy as np
from PIL import ImageGrab
import subprocess
import time

def record_screen():
    # Define the screen resolution
    screen_width, screen_height = 1440, 900  # Adjust this to match your screen resolution
    fps = 30  # Target FPS for recording

    # Define the ffmpeg command
    ffmpeg_cmd = [
        'ffmpeg',
        '-y',  # Overwrite output file if it exists
        '-f', 'rawvideo',
        '-vcodec', 'rawvideo',
        '-pix_fmt', 'bgr24',
        '-s', f'{screen_width}x{screen_height}',  # Size of one frame
        '-r', str(fps),  # Input frames per second
        '-i', '-',  # Input from pipe
        '-an',  # No audio
        '-vcodec', 'libx264',
        '-pix_fmt', 'yuv420p',
        '-crf', '18',  # Higher quality
        '-preset', 'medium',  # Encoding speed
        'screen_recording.mp4'
    ]

    # Start the ffmpeg process
    ffmpeg_process = subprocess.Popen(ffmpeg_cmd, stdin=subprocess.PIPE)

    frame_count = 0
    start_time = time.time()

    while True:
        # Capture the screen
        img = ImageGrab.grab()
        img_np = np.array(img)

        # Convert and resize the frame
        frame = cv2.cvtColor(img_np, cv2.COLOR_RGB2BGR)
        resized_frame = cv2.resize(frame, (screen_width, screen_height))

        # Write the frame to ffmpeg
        ffmpeg_process.stdin.write(resized_frame.tobytes())

        # Display the frame
        cv2.imshow('Screen Recording', resized_frame)

        # Stop recording when 'q' is pressed
        if cv2.waitKey(1) & 0xFF == ord('q'):
            break

    # Close the ffmpeg process
    ffmpeg_process.stdin.close()
    ffmpeg_process.wait()

    # Release everything when job is finished
    cv2.destroyAllWindows()

if __name__ == "__main__":
    record_screen()




  


  As you can see, it should be 30 frames per second, but the problem is that when I open the file afterwards its all sped up. I think it has to do with the frame capture rate as oppose to the encoded rate. I'm not quite sure though. If I try to speed the video down afterwards so that it plays in real time the video is just really choppy. And the higher I make the fps, the faster the video plays, meaning the more I have to slow it down and then its still choppy. I'm pretty sure that it captures frames at a really slow rate and then puts them in a video and plays it back at 30fps. Can anyone fix this ? Anything that gets a working screen recorder on mac os I will take.