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• Freeze when writing ffmpeg execution result to io.Pipe

  7 novembre 2023, par alex

  I am writing a wrapper to work with exec.Cmd to work with io.Pipe. The wrapper is intended to simplify work with the file system, I want to convert a video, write the result of the conversion to io.Pipe, read it in the goroutine and transfer it to make a preview of the new converted file. For this purpose I use FFmpeg. But I've encountered a problem, when I start the test the execution just hangs and I can't get any result, but there are no errors, everything just hangs.

  


  CmdRunner source code

  


  type CmdRunner struct {
    commander Commander
    StdIn io.ReadCloser
    StdoutWriter io.WriteCloser
    StdErrWriter io.Writer
}

func (c *CmdRunner) RunByPipe(ctx context.Context) error {
    //done := make(chan error)
    name, args := c.commander.Command()
    cmd := exec.CommandContext(ctx, name, args...)

    if c.StdIn != nil {
        fmt.Print("RunByPipe STDIN\n")
        cmd.Stdin = c.StdIn
    }

    if c.StdoutWriter != nil {
        fmt.Print("RunByPipe STDOUT\n")
        cmd.Stdout = c.StdoutWriter
    }

    stderr := bytes.Buffer{}
    cmd.Stderr = &stderr

    if err := cmd.Start(); err != nil {
        return err
    }

    if err := cmd.Wait(); err != nil {
        return err
    }

    if stderr.String() != "" {
        return fmt.Errorf("want empty stderr, but got %s", stderr.String())
    }

    return nil
}



  


  Unit test code

  


  type TestCommander struct {
    name string
    args []string
}

func (c *TestCommander) SetCommand(name string, args []string) {
    c.name = name
    c.args = args
}

func (c *TestCommander) Command() (string, []string) {
    return c.name, c.args
}

func TestConvert(t *testing.T) {
    ctx := context.Background()
    filePath := "testdata/input_mp4.mp4"
    data, err := convertFile(filePath, ctx)
    outFile := "testdata/output_mp4.mp4"
    if err != nil {
        fmt.Print("ERR: ", err, "\n")
    }

    os.WriteFile(outFile, data, 0644)

}

func convertFile(filePath string, ctx context.Context) (bytes []byte, err error) {
    // Create a CmdRunner instance with your custom Commander.
    runner := &CmdRunner{}
    commander := &TestCommander{}
    args := []string{
        "-nostats",
        "-i", filePath,
        "-y",
        "-loglevel", "0",
        "-filter:v", "fps=30, crop=trunc(iw/2)*2:trunc(ih/2)*2",
        "-c:v", "libx264",
        "-c:a", "aac",
        "-pix_fmt", "yuv420p",
        "-movflags", "frag_keyframe+faststart",
        "-bufsize", "24M",
        "-maxrate", "12M",
        "-f", "mp4",
        "pipe:1",
    }

    commander.SetCommand("ffmpeg", args)
    runner.SetCommander(commander)
    outputPipeReader, outputPipeWriter := io.Pipe()
    runner.SetStdOutWriter(outputPipeWriter)

    wg := &sync.WaitGroup{}
    wg.Add(1)
    go func() {
        defer outputPipeReader.Close()
        defer wg.Done()

        // Read data from output pipe
        bytes, err = io.ReadAll(outputPipeReader)
        if err != nil {
            fmt.Print("\nReadAll err: ", err, "\n")
        }
    }()

    err = runner.RunByPipe(ctx)
    if err != nil {
        fmt.Print("\nRunByPipe err: ", err, "\n")
        return
    }

    wg.Wait()

    return
}


  


  I can't find a clue as to what might have gone wrong.
P.S : But if I remove if err := cmd.Wait(); err != nil { return err } Then the problem goes away, but there will be no data, because nothing is written to io.Pipe.Why ?

  


• How to create a video from svg files using a pipe with ffmpeg ?

  5 juillet 2023, par Max Chr.

  I want to create a video from svg graphic stored in a database. My procedure would be the following to archive that :

  


  

  1. connect to database

  


  2. create ffmpeg command which takes a pipe as input

  


  3. spawn the ffmpeg child process

  


  4. Wait for the output of the process.

  


  


  start another thread :
For all svg files do :

  


  

  1. download the svg from the database into a byte buffer

  


  2. write the byte buffer to stdin of the ffmpeg child process

  


  


  When running my code I encounter a problem when piping the svg files to ffmpeg.
Another possibility would be to download all the svg files to a temp directory and then using ffmpeg, but I want to avoid this.

  


  I used ffmpeg -f image2pipe -c:v svg -i - -c:v libx264 -y Downloads/out.mp4. But then ffmpeg gives me the following error :

  


  [image2pipe @ 0x562ebd74c300] Could not find codec parameters for stream 0 (Video: svg (librsvg), none): unspecified size
Consider increasing the value for the 'analyzeduration' (0) and 'probesize' (5000000) options


  


  I found out that there's a svg_pipe format in ffmpeg, so I tried that - without success, same error.

  


  Do you have any ideas how to make this work ?

  


• Broken Pipe Error [Errno 32] after saving more than ten PNG images using PIL

  6 septembre 2019, par Blinko

  I am using the ffmpeg pipeline to compress a series of png frames and output an mp4 video, while also saving each frame as a separate png image. The problem is that every time I run the script, I get a Broken Pipe error on the 11th image :

  Traceback (most recent call last):
  
    File "/anaconda3/envs/tensorflow/lib/python3.6/site-packages/PIL/ImageFile.py", line 487, in _save
  
      fh = fp.fileno()
  
  AttributeError: '_idat' object has no attribute 'fileno'
  
  
  
  During handling of the above exception, another exception occurred:
  
  
  
  Traceback (most recent call last):
  
    File "gen_clip.py", line 173, in <module>
  
      main()
  
    File "gen_clip.py", line 167, in main
  
      ts_pos = (0,frame.samplesperbeam-50)
  
    File "/Users/Amanda/Desktop/data/pyARIS.py", line 1028, in make_video
  
      im.save(pipe.stdin, 'PNG')
  
    File "/anaconda3/envs/tensorflow/lib/python3.6/site-packages/PIL/Image.py", line 1994, in save
  
      save_handler(self, fp, filename)
  
    File "/anaconda3/envs/tensorflow/lib/python3.6/site-packages/PIL/PngImagePlugin.py", line 868, in _save
  
      [("zip", (0, 0)+im.size, 0, rawmode)])
  
    File "/anaconda3/envs/tensorflow/lib/python3.6/site-packages/PIL/ImageFile.py", line 502, in _save
  
      fp.write(d)
  
    File "/anaconda3/envs/tensorflow/lib/python3.6/site-packages/PIL/PngImagePlugin.py", line 730, in write
  
      self.chunk(self.fp, b"IDAT", data)
  
    File "/anaconda3/envs/tensorflow/lib/python3.6/site-packages/PIL/PngImagePlugin.py", line 717, in putchunk
  
      fp.write(data)
  
  BrokenPipeError: [Errno 32] Broken pipe
  
  </module>

  I am not too familiar with PIL or ffmpeg, so I am not sure whether it’s a problem with the pipe parameters that I am passing in or something to do with the code itself. No matter what the starting frame number is, the error always appears after 10 images are saved.

  Here is the array of pipe parameters I’m sending to the command prompt :

  command = ['ffmpeg',
  
         '-y',
  
         '-f', 'image2pipe',
  
         '-vcodec', 'png',
  
         '-r', '1',
  
         '-r', str(fps), # frames per second
  
         '-i', '-', # The input comes from a pipe
  
         '-an', # Tells FFMPEG not to expect any audio
  
         '-vcodec', 'mpeg4',
  
         '-b:v', '5000k',
  
         '../'+filename+"/"+filename+".mp4",
  
         '-hide_banner',
  
         '-loglevel', 'panic']

  This is the loop that generates and saves each image :

      for i in tqdm.tqdm(range(start_frame, end_frame)):
  
          frame = FrameRead(data, i)
  
          frame_image = np.zeros([ydim, xdim], dtype=np.uint8)
  
          frame_image[image_write_rows, image_write_cols] = frame.frame_data[sample_read_rows, sample_read_cols]
  
  
  
          all_frame_data.append(frame.frame_data)
  
          im = Image.fromarray(cm(frame_image, bytes=True))
  
  
  
          if timestamp == True:
  
              ts = str(datetime.datetime.fromtimestamp(frame.sonartimestamp/1000000, pytz.timezone('UTC')).strftime('%Y-%m-%d %H:%M:%S'))
  
              text = "%s\n%d" % (ts, i)
  
              draw = ImageDraw.Draw(im)
  
              draw.text(ts_pos,text,font=font, fill = 'white')
  
  
  
          im.save(directory+filename+'/frames/'+str(i)+'_'+str(frame.sonartimestamp)+'_'+filename+'.png'  , "PNG")
  
          im.save(pipe.stdin, 'PNG')
  
          j += 1

  I am running this on MacOS, Python 3.6. Help on the cause of the error and/or possible solutions will be greatly appreciated !