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• ffmpeg weird x264 encoding behavior

  1er février 2016, par JMor

  I have a captured a 720x480 video with a display aspect ratio of 16:9 which I want to crop, resize and pad, but just the x264 encoding command is giving me a headache.

  (Screenshot of input.m2v) Here is my command :

  ffmpeg -ss 1861 -i input.m2v -c:v libx264 -profile:v main -preset:v medium -level 3.1 -x264opts crf=21.228 -t 60 -y -f mp4 output.mp4

  And here is the ffmpeg output :

  (Screen shot of output.mp4)

  Input #0, mpegvideo, from 'input.m2v':
  
    Duration: N/A, bitrate: N/A
  
      Stream #0:0: Video: mpeg2video (Main), yuv420p(tv), 720x480 [SAR 32:27 DAR 1
  
  6:9], max. 6605 kb/s, 31.02 fps, 59.94 tbr, 1200k tbn, 59.94 tbc
  
  [libx264 @ 02ba84c0] using SAR=32/27
  
  [libx264 @ 02ba84c0] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2 AVX
  
  [libx264 @ 02ba84c0] profile Main, level 3.1
  
  [libx264 @ 02ba84c0] 264 - core 144 r2525 40bb568 - H.264/MPEG-4 AVC codec - Cop
  
  yleft 2003-2014 - http://www.videolan.org/x264.html - options: cabac=1 ref=3 deb
  
  lock=1:0:0 analyse=0x1:0x111 me=hex subme=7 psy=1 psy_rd=1.00:0.00 mixed_ref=1 m
  
  e_range=16 chroma_me=1 trellis=1 8x8dct=0 cqm=0 deadzone=21,11 fast_pskip=1 chro
  
  ma_qp_offset=-2 threads=12 lookahead_threads=2 sliced_threads=0 nr=0 decimate=1
  
  interlaced=0 bluray_compat=0 constrained_intra=0 bframes=3 b_pyramid=2 b_adapt=1
  
   b_bias=0 direct=1 weightb=1 open_gop=0 weightp=2 keyint=250 keyint_min=25 scene
  
  cut=40 intra_refresh=0 rc_lookahead=40 rc=crf mbtree=1 crf=21.2 qcomp=0.60 qpmin
  
  =0 qpmax=69 qpstep=4 ip_ratio=1.40 aq=1:1.00
  
  Output #0, mp4, to 'output.mp4':
  
    Metadata:
  
      encoder         : Lavf56.19.100
  
      Stream #0:0: Video: h264 (libx264) ([33][0][0][0] / 0x0021), yuv420p, 720x48
  
  0 [SAR 32:27 DAR 16:9], q=-1--1, 29.97 fps, 30k tbn, 29.97 tbc
  
      Metadata:
  
        encoder         : Lavc56.21.102 libx264
  
  Stream mapping:
  
    Stream #0:0 -> #0:0 (mpeg2video (native) -> h264 (libx264))

  The output size is 720x480, displayed as 853x480, as expected.
  But it looks like the frame has been vertically scaled by a factor of 1.18 and then cropped to a height of 480, so that I am losing the top and bottom of the frame. In fact, the behavior is equivalent to :

  -vf "scale=720:569,crop=720:480:0:0"

  Although I assume the aspect ratio plays a part here (I think the 1.18 factor is really (16/9)/(720/480)) I am surprised that ffmpeg would do that out of the blue. May be someone more knowledgeable than me could explain it ?

• ffmpeg weird x264 encoding behavior

  1er février 2016, par JMor

  I have a captured a 720x480 video with a display aspect ratio of 16:9 which I want to crop, resize and pad, but just the x264 encoding command is giving me a headache.

  (Screenshot of input.m2v) Here is my command :

  ffmpeg -ss 1861 -i input.m2v -c:v libx264 -profile:v main -preset:v medium -level 3.1 -x264opts crf=21.228 -t 60 -y -f mp4 output.mp4

  And here is the ffmpeg output :

  (Screen shot of output.mp4)

  Input #0, mpegvideo, from 'input.m2v':
  
    Duration: N/A, bitrate: N/A
  
      Stream #0:0: Video: mpeg2video (Main), yuv420p(tv), 720x480 [SAR 32:27 DAR 1
  
  6:9], max. 6605 kb/s, 31.02 fps, 59.94 tbr, 1200k tbn, 59.94 tbc
  
  [libx264 @ 02ba84c0] using SAR=32/27
  
  [libx264 @ 02ba84c0] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2 AVX
  
  [libx264 @ 02ba84c0] profile Main, level 3.1
  
  [libx264 @ 02ba84c0] 264 - core 144 r2525 40bb568 - H.264/MPEG-4 AVC codec - Cop
  
  yleft 2003-2014 - http://www.videolan.org/x264.html - options: cabac=1 ref=3 deb
  
  lock=1:0:0 analyse=0x1:0x111 me=hex subme=7 psy=1 psy_rd=1.00:0.00 mixed_ref=1 m
  
  e_range=16 chroma_me=1 trellis=1 8x8dct=0 cqm=0 deadzone=21,11 fast_pskip=1 chro
  
  ma_qp_offset=-2 threads=12 lookahead_threads=2 sliced_threads=0 nr=0 decimate=1
  
  interlaced=0 bluray_compat=0 constrained_intra=0 bframes=3 b_pyramid=2 b_adapt=1
  
   b_bias=0 direct=1 weightb=1 open_gop=0 weightp=2 keyint=250 keyint_min=25 scene
  
  cut=40 intra_refresh=0 rc_lookahead=40 rc=crf mbtree=1 crf=21.2 qcomp=0.60 qpmin
  
  =0 qpmax=69 qpstep=4 ip_ratio=1.40 aq=1:1.00
  
  Output #0, mp4, to 'output.mp4':
  
    Metadata:
  
      encoder         : Lavf56.19.100
  
      Stream #0:0: Video: h264 (libx264) ([33][0][0][0] / 0x0021), yuv420p, 720x48
  
  0 [SAR 32:27 DAR 16:9], q=-1--1, 29.97 fps, 30k tbn, 29.97 tbc
  
      Metadata:
  
        encoder         : Lavc56.21.102 libx264
  
  Stream mapping:
  
    Stream #0:0 -> #0:0 (mpeg2video (native) -> h264 (libx264))

  The output size is 720x480, displayed as 853x480, as expected.
  But it looks like the frame has been vertically scaled by a factor of 1.18 and then cropped to a height of 480, so that I am losing the top and bottom of the frame. In fact, the behavior is equivalent to :

  -vf "scale=720:569,crop=720:480:0:0"

  Although I assume the aspect ratio plays a part here (I think the 1.18 factor is really (16/9)/(720/480)) I am surprised that ffmpeg would do that out of the blue. May be someone more knowledgeable than me could explain it ?

• Why codecs x264/x265 ignores pts and dts of input frame ?

  1er mars 2018, par Iceman

  I’m trying to encode images from a webcam with libx265 (libx264 tried earlier) ...
  The webcam can not shoot with stable FPS because of the different amount of light entering the matrix and, as a result, different delays. Therefore, I count the fps and dts of the incoming frame and set these values for the corresponding parameters of the x265_image object, and init the encoder fpsNum with 1000 and fpsDenom with 1 (for millisecond timebase).
  The problem is that the encoder ignores pts and dts of input image and encodes at 1000 fps ! The same trick with timebase produces smooth record with libvpx. Why it does not work with x264/x265 codecs ?

  Here is parameters initialization :

  ...
  
      error = (x265_param_default_preset(param, "fast", "zerolatency") != 0);
  
      if(!error){
  
          param->sourceWidth = width;
  
          param->sourceHeight = height;
  
          param->frameNumThreads = 1;
  
          param->fpsNum = 1000;
  
          param->fpsDenom =  1;
  
          // Intra refres:
  
          param->keyframeMax = 15;
  
          param->intraRefine = 1;
  
          // Rate control:
  
          param->rc.rateControlMode = X265_RC_CQP;
  
          param->rc.rfConstant = 12;
  
          param->rc.rfConstantMax = 48;
  
          // For streaming:
  
          param->bRepeatHeaders = 1;
  
          param->bAnnexB = 1;
  
          encoder = x265_encoder_open(param);
  
          ...
  
      }
  
  ...

  Here is frame adding function :

  bool hevc::Push(unsigned char *data){
  
      if(!error){
  
          std::lock_guard lock(m_framestack);
  
          if( timer > 0){
  
              framestack.back()->dts = clock() - timer;
  
              timer+= framestack.back()->dts;
  
          }
  
          else{timer = clock();}
  
          x265_picture *picture = x265_picture_alloc();
  
          if( picture){
  
              x265_picture_init(param, picture);
  
              picture->height = param->sourceHeight;
  
              picture->stride[0] = param->sourceWidth;
  
              picture->stride[1] = picture->stride[2] = picture->stride[0] / 2;
  
              picture->planes[0] = new char[  luma_size];
  
              picture->planes[1] = new char[chroma_size];
  
              picture->planes[2] = new char[chroma_size];
  
  
  
              colorspaces::BGRtoI420(param->sourceWidth, param->sourceHeight, data, (byte*)picture->planes[0], (byte*)picture->planes[1], (byte*)picture->planes[2]);
  
              picture->pts = picture->dts = 0;
  
              framestack.emplace_back(picture);
  
          }
  
          else{error = true;}
  
      }
  
      return !error;
  
  }

  Global PTS is increasing right after x265_encoder_encode call :
  pts+= pic_in->dts; and sets as a pts of new image from framestack queue when it comes to encoder.

  Can the x265/x264 codecs encode at variable fps ? How to configure it if yes ?