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• Writing numpy arrays using cv2 VideoWriter

  8 juillet 2015, par JustInTime

  I have a problem with writing a toy example video using opencv2.3.1 VideoWriter, here is how I do it :

  writer = cv2.VideoWriter('test1.avi',cv.CV_FOURCC('P','I','M','1'),25,(640,480))
  
  for i in range(1000):
  
      x = np.random.randint(10,size=(480,640)).astype('uint8')
  
      writer.write(x)
  
  #del writer (with or without tested)

  I tried every possible combination resulting with a 0 bytes file if the extension was mpg, and 5.5kb if it was avi. I should say that some pointed out that I should build the ffmpeg library from source and not apt-get it. Well I did that on a fresh machine based on the help of this site http://vinayhacks.blogspot.com/2011/11/installing-opencv-231-with-ffmpeg-on-64.html. which also presented an error while compiling opencv(the error was related to ffmpeg). Now I am really out of ideas, How to generate a video using OPENCV ?

  Thanks in advance

• ffmpeg libx264 AVCodecContext settings

  21 mai 2014, par integra753

  I am using a recent windows (Jan 2011) ffmpeg build and trying to record video in H264. It is recording fine in MPEG4 using the following settings :

  c->codec_id = CODEC_ID_MPEG4;
  
  c->codec_type = AVMEDIA_TYPE_VIDEO;
  
  c->width = VIDEO_WIDTH;
  
  c->height = VIDEO_HEIGHT;
  
  c->bit_rate = c->width * c->height * 4;
  
  c->time_base.den = FRAME_RATE;
  
  c->time_base.num = 1;
  
  c->gop_size = 12;
  
  c->pix_fmt = PIX_FMT_YUV420P;

  Simply changing CODEC Id to H264 causes avcodec_open() to fail (-1). I found a list of possible settings Encoding h.264 with libavcodec/x264. I have tried these, without setting pix_fmt, avcodec_open() still fails but if I additionally set c->pix_fmt = PIX_FMT_YUV420P ; then I get a divide by zero exception.

  I then came across a few posts on here that say I should set nothing (with exception of code_id, codec_type, width, height and perhaps bit_rate and pix_fmt) as the library now chooses the best settings itself. I have tried various combinations, still avcode_open() fails.

  Does anyone have some advice on what to do or some settings that are current ?

  Thanks.

  Here are one set of H264 settings which give the issue I describe :

  static AVStream* AddVideoStream(AVFormatContext *pOutputFmtCtx, 
  
  int frameWidth, int frameHeight, int fps)
  
  {
  
  AVCodecContext* ctx;
  
  AVStream* stream;
  
  
  
  stream = av_new_stream(pOutputFmtCtx, 0);
  
  if (!stream) 
  
  {
  
      return NULL;
  
  }
  
  
  
  ctx = stream->codec;
  
  
  
  ctx->codec_id = pOutputFmtCtx->oformat->video_codec; //CODEC_ID_H264
  
  ctx->codec_type = AVMEDIA_TYPE_VIDEO;
  
  ctx->width = frameWidth;             //704
  
  ctx->height = frameHeight;           //576
  
  ctx->bit_rate = frameWidth * frameHeight * 4;
  
  
  
  ctx->coder_type = 1;  // coder = 1
  
  ctx->flags|=CODEC_FLAG_LOOP_FILTER;   // flags=+loop
  
  ctx->me_cmp|= 1;  // cmp=+chroma, where CHROMA = 1
  
  ctx->partitions|=X264_PART_I8X8+X264_PART_I4X4+X264_PART_P8X8+X264_PART_B8X8; // partitions=+parti8x8+parti4x4+partp8x8+partb8x8
  
  ctx->me_method=ME_HEX;    // me_method=hex
  
  ctx->me_subpel_quality = 7;   // subq=7
  
  ctx->me_range = 16;   // me_range=16
  
  ctx->gop_size = 250;  // g=250
  
  ctx->keyint_min = 25; // keyint_min=25
  
  ctx->scenechange_threshold = 40;  // sc_threshold=40
  
  ctx->i_quant_factor = 0.71; // i_qfactor=0.71
  
  ctx->b_frame_strategy = 1;  // b_strategy=1
  
  ctx->qcompress = 0.6; // qcomp=0.6
  
  ctx->qmin = 10;   // qmin=10
  
  ctx->qmax = 51;   // qmax=51
  
  ctx->max_qdiff = 4;   // qdiff=4
  
  ctx->max_b_frames = 3;    // bf=3
  
  ctx->refs = 3;    // refs=3
  
  ctx->directpred = 1;  // directpred=1
  
  ctx->trellis = 1; // trellis=1
  
         ctx->flags2|=CODEC_FLAG2_BPYRAMID+CODEC_FLAG2_MIXED_REFS+CODEC_FLAG2_WPRED+CODEC_FLAG2_8X8DCT+CODEC_FLAG2_FASTPSKIP;  // flags2=+bpyramid+mixed_refs+wpred+dct8x8+fastpskip
  
  ctx->weighted_p_pred = 2; // wpredp=2
  
  // libx264-main.ffpreset preset
  
  ctx->flags2|=CODEC_FLAG2_8X8DCT;
  
  ctx->flags2^=CODEC_FLAG2_8X8DCT;    // flags2=-dct8x8
  
  
  
  // if set this get divide by 0 error on avcodec_open()
  
  // if don't set it get -1 error on avcodec_open()
  
  //ctx->pix_fmt = PIX_FMT_YUV420P; 
  
  
  
  return stream;

  }

• ffmpeg libx264 AVCodecContext settings

  21 mai 2014, par integra753

  I am using a recent windows (Jan 2011) ffmpeg build and trying to record video in H264. It is recording fine in MPEG4 using the following settings :

  c->codec_id = CODEC_ID_MPEG4;
  
  c->codec_type = AVMEDIA_TYPE_VIDEO;
  
  c->width = VIDEO_WIDTH;
  
  c->height = VIDEO_HEIGHT;
  
  c->bit_rate = c->width * c->height * 4;
  
  c->time_base.den = FRAME_RATE;
  
  c->time_base.num = 1;
  
  c->gop_size = 12;
  
  c->pix_fmt = PIX_FMT_YUV420P;

  Simply changing CODEC Id to H264 causes avcodec_open() to fail (-1). I found a list of possible settings Encoding h.264 with libavcodec/x264. I have tried these, without setting pix_fmt, avcodec_open() still fails but if I additionally set c->pix_fmt = PIX_FMT_YUV420P ; then I get a divide by zero exception.

  I then came across a few posts on here that say I should set nothing (with exception of code_id, codec_type, width, height and perhaps bit_rate and pix_fmt) as the library now chooses the best settings itself. I have tried various combinations, still avcode_open() fails.

  Does anyone have some advice on what to do or some settings that are current ?

  Thanks.

  Here are one set of H264 settings which give the issue I describe :

  static AVStream* AddVideoStream(AVFormatContext *pOutputFmtCtx, 
  
  int frameWidth, int frameHeight, int fps)
  
  {
  
  AVCodecContext* ctx;
  
  AVStream* stream;
  
  
  
  stream = av_new_stream(pOutputFmtCtx, 0);
  
  if (!stream) 
  
  {
  
      return NULL;
  
  }
  
  
  
  ctx = stream->codec;
  
  
  
  ctx->codec_id = pOutputFmtCtx->oformat->video_codec; //CODEC_ID_H264
  
  ctx->codec_type = AVMEDIA_TYPE_VIDEO;
  
  ctx->width = frameWidth;             //704
  
  ctx->height = frameHeight;           //576
  
  ctx->bit_rate = frameWidth * frameHeight * 4;
  
  
  
  ctx->coder_type = 1;  // coder = 1
  
  ctx->flags|=CODEC_FLAG_LOOP_FILTER;   // flags=+loop
  
  ctx->me_cmp|= 1;  // cmp=+chroma, where CHROMA = 1
  
  ctx->partitions|=X264_PART_I8X8+X264_PART_I4X4+X264_PART_P8X8+X264_PART_B8X8; // partitions=+parti8x8+parti4x4+partp8x8+partb8x8
  
  ctx->me_method=ME_HEX;    // me_method=hex
  
  ctx->me_subpel_quality = 7;   // subq=7
  
  ctx->me_range = 16;   // me_range=16
  
  ctx->gop_size = 250;  // g=250
  
  ctx->keyint_min = 25; // keyint_min=25
  
  ctx->scenechange_threshold = 40;  // sc_threshold=40
  
  ctx->i_quant_factor = 0.71; // i_qfactor=0.71
  
  ctx->b_frame_strategy = 1;  // b_strategy=1
  
  ctx->qcompress = 0.6; // qcomp=0.6
  
  ctx->qmin = 10;   // qmin=10
  
  ctx->qmax = 51;   // qmax=51
  
  ctx->max_qdiff = 4;   // qdiff=4
  
  ctx->max_b_frames = 3;    // bf=3
  
  ctx->refs = 3;    // refs=3
  
  ctx->directpred = 1;  // directpred=1
  
  ctx->trellis = 1; // trellis=1
  
         ctx->flags2|=CODEC_FLAG2_BPYRAMID+CODEC_FLAG2_MIXED_REFS+CODEC_FLAG2_WPRED+CODEC_FLAG2_8X8DCT+CODEC_FLAG2_FASTPSKIP;  // flags2=+bpyramid+mixed_refs+wpred+dct8x8+fastpskip
  
  ctx->weighted_p_pred = 2; // wpredp=2
  
  // libx264-main.ffpreset preset
  
  ctx->flags2|=CODEC_FLAG2_8X8DCT;
  
  ctx->flags2^=CODEC_FLAG2_8X8DCT;    // flags2=-dct8x8
  
  
  
  // if set this get divide by 0 error on avcodec_open()
  
  // if don't set it get -1 error on avcodec_open()
  
  //ctx->pix_fmt = PIX_FMT_YUV420P; 
  
  
  
  return stream;

  }