Recherche avancée

Sur d’autres sites (9186)

• How to prescale a frame using ffmpeg and H.265

  20 juillet 2017, par akw

  I want to decode video frames with the H.265 coded (AV_CODEC_ID_HEVC)
  I use the following code :

  AVCodec *hevcCodec = avcodec_find_decoder(AV_CODEC_ID_HEVC);
  
  AVCodecContext *avctx  = avcodec_alloc_context3(hevcCodec);
  
  avcodec_open2(avctx, hevcCodec, 0);
  
  AVFrame *frame = av_frame_alloc();
  
  AVPacket pkt;
  
  av_init_packet(&pkt);
  
  pkt.data = myDataPtr;
  
  pkt.size = myDataSize;
  
  int got_frame = 0;
  
  avcodec_send_packet(avctx, &pkt);
  
  if (avcodec_receive_frame(avctx, frame) >=0 ) {
  
          got_frame = 1;
  
          ...
  
  }

  This works fine, I got my YUV frame and can process it further (like converting to RGB or scaling, etc.)
  However, I would like to somehow tell the ffmpeg library, to scale the AVFrame while decoding (a scale factor of a power of 2 would be sufficient).
  I don’t want to scale after converting to RGB or use swscale or anything. I have to decode a lot of frames and need a smaller resolution.

  Is it possible to give the AVCodecContext some hints to scale the frames ?
  (I tried setting avctx.width and avctx.height, but this did not help)

• ppc : Clarify and extend the cpuid check

  10 mai 2015, par Luca Barbato

  ppc : Clarify and extend the cpuid check
  Add POWER entries.
  

  • [DBH] libavutil/ppc/cpu.c

• Spawned ffmpeg process in nodejs Transform stream with flow control doesn't process input stream

  30 septembre 2022, par user1832894

  I have implemented a node.js Transform stream class that spawns ffmpeg and streams out the transformed stream at a controlled realtime rate. Below is my _transform() method.

  


  this.rcvd += chunk.length
console.log('received bytes %d', this.rcvd)
const ready = this.ffmpeg.stdin.write(chunk, encoding, err => err
  ? cb(err)
  : ready
    ? cb
    : this.ffmpeg.stdin.once('drain', cb))


  


  I want to write to ffmpeg's stdin stream till it returns false, at which point I wait for the drain event to write more data.

  


  Concurrently, I have a timer that fires every 40 milliseconds that reads ffmpeg's stdout and pushes it to the Transform stream's output (the readable side). Code not complete, but the folllowing describes it well.

  


  const now = Date.now()
const bytesToTransmit = (now - this.lastTx) * 32

const buf = this.ffmpeg.stdout.read()

if (buf == null) return

if (buf.length <= bytesToTransmit) {
  this.push(buf)
  this.lastTx += buf.length * 32
  return
}

this.push(buf.slice(0, bytesToTransmit))
this.lastTx = now

// todo(handle pending buffer)
this.pending = buf.slice(bytesToTransmit)


  


  The issue I am facing is that the first write (of 65k bytes) returns false, and after that I never receive the drain event. FFMpeg doesn't start processing the data until certain amount of data (256k bytes in my case) has been written, and once I start waiting for the drain event, I never recover control.

  


  I've tried a few ffmpeg options like nobuffer but to no avail. What am I doing wrong ? Any ideas would be super helpful.

  


  Thanks !