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• mp4 video written with ffmpeg has different first frame based on total number of frames

  25 janvier 2023, par Nitzan Weissman

  I have a code that writes and reads videos in Python, I'm doing the writing using ffmpeg. I noticed a weird phenomenon, where the first frame changes based on the total number of frames in the video. I find it weird because the first frame is a key frame (I checked it using ffprobe)

  


  The code I'm using :

  


  The writing function

  


  import shutil
import subprocess
def write_h264_video(video_path: str, images: np.ndarray, fps: float):
    image_name_template = '00%04d.png'
    tmp_image_dir = (Path(video_path).parent / 'tmp_imgs')
    tmp_image_dir.mkdir()

    for ii, image in enumerate(images):
        cv2.imwrite(f'{str(tmp_image_dir / str(ii).zfill(6))}.png', image[..., ::-1])    
    command = f'ffmpeg -hide_banner -loglevel error -framerate {fps} -y -i {tmp_image_dir}/{image_name_template} ' \
            f' -c:v libx264 -pix_fmt yuv420p {video_path} -y'
    subprocess.call(command, shell=True)
    shutil.rmtree(tmp_image_dir)


  


  The main code

  


  import numpy as np
from pathlib import Path
import decord
decord.bridge.set_bridge('torch')

input_video_path = Path('')
tmp_path = Path('')
input_video = decord.VideoReader(str(input_video_path))

frames = np.zeros((20, 512, 512, 3), dtype = np.uint8)
for i in range(20):
    frames[i] = input_video[i].detach().cpu().numpy()
    
long_video_path = tmp_path / 'long_video.mp4'
short_video_path = tmp_path / 'short_video.mp4'

fps = 30
write_h264_video(str(long_video_path), frames, fps=fps)
write_h264_video(str(short_video_path), frames[:10], fps=fps)


long_video = decord.VideoReader(str(long_video_path))
short_video = decord.VideoReader(str(short_video_path))

long_frame_0 = long_video[0]
short_frame_0 = short_video[0]
(long_frame_0 == short_frame_0).all()


  


  I am supposed to get True, but I'm getting False.
I tried reading using other methods, using opencv for example, and the issue persists.
There are other ways to write videos of course, but I'm interested in ffmpeg-based ways.

  


  Thanks !

  


• FFmpeg max audio overhead

  15 août 2020, par Alsors

  So I'm encoding videos with FFmpeg. I've set the video stream to have a maximum rate of 6840 kbps and the audio stream to have a constant rate of 160 kbps (AAC) so once they're added together it's a maximum combined rate of 7000 kbps (the maximum rate before my video sharing service re-encodes the video and audio). The problem is sometimes the audio stream likes to go above it's designated constant rate (not by much however enough to take it over 7000 kbps), even with the exact same command it'll sometimes go above and sometime stay the same.

  


  My question : is there a way to calculate the maximum overhead of the audio stream ? I'm assuming FFmpeg has a point where it will not allow the audio rate to go any higher ? What is that exact rate ?

  


• Call FFmpeg via JavaCPP：Caused by : java.lang.NoClassDefFoundError : Could not initialize class org.bytedeco.javacpp.avformat$AVFormatContext

  8 décembre 2017, par Xuan

  In CentOS, use javacpp call FFmpeg to do video cropping a frame, in my own development machine using this code is no problem, but in centos6 reported NoClassDefFound : Could not initialize class org.bytedeco.javacpp.avutil

  Caused by: java.lang.NoClassDefFoundError: Could not initialize class org.bytedeco.javacpp.avformat$AVFormatContext
  
      at org.bytedeco.javacv.FFmpegFrameGrabber.startUnsafe(FFmpegFrameGrabber.java:383) ~[javacv-1.0.jar:1.0]
  
      at org.bytedeco.javacv.FFmpegFrameGrabber.start(FFmpegFrameGrabber.java:377) ~[javacv-1.0.jar:1.0]
  
      at cn.xxtui.support.upload.BasicUpload.convertImage(BasicUpload.java:211) ~[classes/:?]
  
      at cn.xxtui.support.upload.BasicUpload.upload(BasicUpload.java:197) ~[classes/:?]
  
      at cn.com.ql.wiseBeijing.upload.UploadImage.upload(UploadImage.java:144) ~[classes/:?]
  
      at cn.com.ql.wiseBeijing.upload.UploadImage.imageCategory(UploadImage.java:51) ~[classes/:?]
  
      at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:1.7.0_25]
  
      at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57) ~[?:1.7.0_25]
  
      at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:1.7.0_25]
  
      at java.lang.reflect.Method.invoke(Method.java:606) ~[?:1.7.0_25]
  
      at org.apache.cxf.service.invoker.AbstractInvoker.performInvocation(AbstractInvoker.java:180) ~[cxf-core-3.1.12.jar:3.1.12]
  
      at org.apache.cxf.service.invoker.AbstractInvoker.invoke(AbstractInvoker.java:96) ~[cxf-core-3.1.12.jar:3.1.12]
  
      ... 37 more

  This is my pom configuration：

  <dependency>
  
      <groupid>org.bytedeco</groupid>
  
      <artifactid>javacv</artifactid>
  
      <version>1.0</version>
  
  </dependency>
  
  <dependency>
  
      <groupid>org.bytedeco</groupid>
  
      <artifactid>javacpp</artifactid>
  
      <version>1.0</version>
  
  </dependency>
  
  <dependency>
  
      <groupid>com.github.hoary.ffmpeg</groupid>
  
      <artifactid>FFmpeg-linux-x86_64</artifactid>
  
      <version>2.0.1.1
  
      </version>
  
  </dependency>
  
  <dependency>
  
      <groupid>org.bytedeco.javacpp-presets</groupid>
  
      <artifactid>ffmpeg</artifactid>
  
      <version>2.7.1-1.0</version>
  
  </dependency>

  This is my code：

  public String convertImage(String filePath, String imagePath) throws IOException, FrameGrabber.Exception {
  
      FFmpegFrameGrabber g = new FFmpegFrameGrabber(filePath);
  
      g.start();
  
      Java2DFrameConverter java2DFrameConverter = new Java2DFrameConverter();
  
      BufferedImage bufferedImage = java2DFrameConverter.convert(g.grabImage());
  
      String path = imagePath + System.currentTimeMillis() + ".png";
  
      ImageIO.write(bufferedImage, "png", new File(path));
  
      g.stop();
  
      return path;
  
  }