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• lavd/xcbgrab : do not try to create refcounted packets.

  23 octobre 2016, par Nicolas George

  lavd/xcbgrab : do not try to create refcounted packets.
  The framework will allocate a buffer and copy the data to it,
  
  that takes time. But it avoids constently creating and
  
  destroyng the shared memory segment, and that saves more time.
  On my setup,
  
  from 200 to 300 FPS at full screen (1920×1200),
  
  from 1400 to 3300 at smaller size (640×480),
  
  similar to legacy x11grab and confirmed by others.
  Plus, shared memory segments are a scarce resource,
  
  allocating potentially many is a bad idea.
  Note : if the application were to drop all references to the
  
  buffer before the next call to av_read_frame(), then passing
  
  the shared memory segment as a refcounted buffer would be
  
  even more efficient, but it is hard to guarantee, and it does
  
  not happen with the ffmpeg command-line tool. Using a small
  
  number of preallocated buffers and resorting to a copy when
  
  the pool is exhausted would be a solution to get the better
  
  of both worlds.
  

  • [DH] libavdevice/xcbgrab.c

• ffmpeg : recode transport stream (MPEG2 or h264) to another transport stream (h264)

  14 juin 2017, par MatMike

  currently, I’m struggling with a task I want to implement using a perl script on a Synology DiskStation.
  What I’m not sure about is the ffmpeg command to use.
  Actually, the DiskStation supports hardware encoding and it works quite well encoding to MKV files. The only thing that’s missing : I don’t want to encode to MKV as it’s hard to work on these files with my other software for cutting.
  Therefore, I’d like to encode to a transport stream again.
  I’m using this command at the moment :

  sudo ffmpeg -hide_banner -loglevel verbose -vaapi_device /dev/dri/renderD128 -i my_input_file.ts -map 0:v -map 0:a -c:v h264_vaapi -vf yadif,format=nv12,hwupload -y -b:v my_bitrate my_output_file.ts

  Now, I always get an error :

  Automatic encoder selection failed for output stream #0:1. Default encoder for format mpegts (codec mp2) is probably disabled. Please choose an encoder manually.
  
  Error selecting an encoder for stream 0:1

  To me it looks like it’s not recognizing that I want to encode using h264 and not the default encoder for transport streams.

  Any ideas on this ?

  Explanation :

  • The mapping is done to get rid of non-supported streams such as teletext and also reduce some streams as I get more than one language stream normally.
  • The sudo is needed as only root is allowed to use vaapi device on Synology (maybe on all systems)

  It would be great if someone could give me a helping hand on this.

  Thanks,
  Matthias

• FFMPEG command works in shell ! but not in my node.js

  29 juillet 2021, par Kuno Kim

  When my ffmpeg command is built by my node.js application it does not run.

  



  error

  



  Unrecognized option 'ss 3.2 -t 1.9 -i videoplayback.mp4 -vf  fps=15,scale=240:-1:flags=lanczos,palettegen palette.png'.


  



  command

  



  ffmpeg -ss 3.2 -t 1.9 -i videoplayback.mp4 -vf \ fps=15,scale=240:-1:flags=lanczos,palettegen palette.png


  



  this is my code

  



  var child_process = require('child_process')

function recordVideo() {

var spawn = child_process.spawn;

var args = [
    '-y', 
    '-ss', '3.2',
    '-t', '1.9', 
    '-i', '../getback/bin/videos/videoplayback.mp4', 
    '-vf', ' \\ ', 
    'fps=', '15', 
    'scale=', '320:-1', 
    'flags=','lanczos,palettegen palette.png', 
];



var ffmpeg = spawn('ffmpeg', args);

ffmpeg.stdout.on('data', function (data) {
    console.log(data);
});

ffmpeg.stderr.on('data', function (data) {
    console.log('grep stderr: ' + data);
});

ffmpeg.on('close', (code) => {
    console.log('child process exited with code ' + code);
}); 
};
recordVideo();


  



  what is this error ?
I think.. 'fps=', '15', In the following code 
 '=' options a problem.

  



  I am still learning English.
I'm sorry if it was hard to understand.