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• Got black screen when recording screen by x11grab device

  30 janvier 2014, par shawnzhu

  I'm trying to record video from a firefox run by xvfb-run but it always output nothing in the video file except black screen.

  Here's what I did :

  start a firefox, open google.com :

  $ xvfb-run firefox https://google.com

  Then it will use the default display server number 99. I can see the display information by command xdpyinfo -display :99.

  A screenshot works very well by command :

  $ xwd -root -silent -display :99.0 | xwdtopnm |pnmtojpeg > screen.jpg

  Start using ffmpeg to record a video :

  $ ffmpeg -f x11grab -i :99.0 out.mpg

  When I play the video file out.mpg, there's black screen all the time.

  Is there any parameter I missed ?

• create a zoom pad effect with ffmpeg but instead of black background put a image background ?

  16 juin 2018, par MIGHTDUY

  i need to create a zoom effect with frame image background instead of black background

  how is possible this

  please help me

  this is my command

  ffmpeg -i duke2.jpg    -filter_complex      "pad=  w=560:h=200:x='(ow-iw)/2':y='(oh-ih)/2',zoompan=  z='zoom+0.002':d=25*4:s=1280x800"    -pix_fmt yuv420p -c:v libx264 zzout.mp4

• ffmpeg got black and white video when encoding flv

  17 décembre 2012, par samyou

  i searched the site and got a post :
  getting black and white image after encoding
  but i got no answer.

  don't know how but it is all black and white.

  hear is the init code :

  JNIEXPORT jboolean JNICALL Java_sam_flvmuxer_SamRTMPNative_nativeInitMuxerAndStart(
  
      JNIEnv *env, jclass jcls, jstring outfile, jint inwidth, jint inheight,
  
      jint fps) {
  
  audioOutBuffer = malloc(AUDIO_OUT_BUFFER_SIZE);
  
  videoOutBuffer = malloc(VIDEO_OUT_BUFFER_SIZE);
  
  VIDEO_WIDTH = inwidth;
  
  VIDEO_HEIGHT = inheight;
  
  av_log_set_callback(samffmpeglogback);
  
  av_register_all();
  
  char *filepath = (*env)->GetStringUTFChars(env, outfile, 0);
  
  JNILOG("file path is %s",filepath);
  
  avformat_alloc_output_context2(&avFormatContext, NULL, NULL, filepath);
  
  if (!avFormatContext) {
  
      JNILOG("avformat_alloc_output_context2 with filepath failed");
  
      return JNI_FALSE;
  
  }
  
  AVOutputFormat *fmt = avFormatContext->oformat;
  
  //fmt->video_codec = VIDEO_CODEC_ID;
  
  ////init video
  
  avVideoStream = avformat_new_stream(avFormatContext, NULL );
  
  if (!avVideoStream) {
  
      (*env)->ReleaseStringUTFChars(env, outfile, filepath);
  
      return 0;
  
  }
  
  
  
  AVCodec *videocodec = avcodec_find_encoder(VIDEO_CODEC_ID);
  
  if (!videocodec) {
  
      JNILOG("avcodec_find_encoder error");
  
      return JNI_FALSE;
  
  }
  
  avcodec_get_context_defaults3(avVideoStream->codec, videocodec);
  
  
  
  AVCodecContext *avVideoCodecContext = avVideoStream->codec;
  
  avVideoCodecContext->codec_type = AVMEDIA_TYPE_VIDEO;
  
  avVideoCodecContext->codec_id = VIDEO_CODEC_ID;
  
  avVideoCodecContext->width = inwidth;
  
  avVideoCodecContext->height = inheight;
  
  avVideoCodecContext->time_base.den = fps;
  
  avVideoCodecContext->time_base.num = 1;
  
  avVideoCodecContext->gop_size = 10;
  
  avVideoCodecContext->pix_fmt = PIX_FMT_YUV420P;
  
  JNILOG("bitrate befort set = %d",avVideoCodecContext->bit_rate);
  
  avVideoCodecContext->bit_rate = 600000;
  
  
  
  
  
  if (fmt->flags & AVFMT_GLOBALHEADER)
  
      avVideoCodecContext->flags |= CODEC_FLAG_GLOBAL_HEADER;
  
  
  
  av_dump_format(avFormatContext,0,filepath,1);
  
  if(avcodec_open2(avVideoCodecContext,videocodec,NULL)<0)
  
  {
  
      JNILOG("video avcodec_open2 failed");
  
      (*env)->ReleaseStringUTFChars(env, outfile, filepath);
  
      return JNI_FALSE;
  
  }
  
  
  
  
  
  
  
  ///////
  
  /* open the output file, if needed */
  
  if (!(fmt->flags & AVFMT_NOFILE)) {
  
      if ((avio_open(&avFormatContext->pb, filepath, AVIO_FLAG_WRITE)) < 0) {
  
          JNILOG("Could not open file!");
  
          (*env)->ReleaseStringUTFChars(env, outfile, filepath);
  
          return 0;
  
      }
  
  }
  
  if (avformat_write_header(avFormatContext, NULL ) < 0) {
  
      JNILOG("Could not avformat_write_header!");
  
      (*env)->ReleaseStringUTFChars(env, outfile, filepath);
  
      return 0;
  
  }
  
  (*env)->ReleaseStringUTFChars(env, outfile, filepath);
  
  YUVFrame = avcodec_alloc_frame();
  
  JNILOG("ffmpeg every thing inited");
  
  return JNI_TRUE;
  
  }

  and encode code looks like below :

  avpicture_fill((AVPicture *)YUVFrame,framedata,PIX_FMT_YUV420P,VIDEO_WIDTH,VIDEO_HEIGHT);
  
      ///打印data 分量!!!!
  
      AVPacket pkt;
  
      av_init_packet(&pkt);
  
      pkt.data = videoOutBuffer;
  
      pkt.size = VIDEO_OUT_BUFFER_SIZE;
  
      int gotpkt = 0;
  
      avcodec_encode_video2(avVideoStream->codec,&pkt,YUVFrame,&gotpkt);
  
      if (gotpkt > 0) {
  
          JNILOG("encoded size=%d,gotpktflag=%d",pkt.size,gotpkt);
  
          pkt.stream_index = avVideoStream->index;
  
          pkt.flags |= AV_PKT_FLAG_KEY;
  
          pkt.pts = timestamp;
  
          while (pkt.pts <= lastVideoPts) {
  
              pkt.pts++;
  
          }
  
          lastVideoPts = pkt.pts;
  
          if (av_interleaved_write_frame(avFormatContext, &pkt) < 0) {
  
              JNILOG("av_interleaved_write_frame failed");
  
          }
  
      }

  someone please help me with this problem^^