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• libavcodec/libx264 do not produce B-frames

  6 novembre 2013, par Rob Schmidt

  I am writing an application in C++ that uses libavcodec with libx264 to encode video. However, the encoded data ended up being much larger than I expected. I analyzed the results and discovered that my encoding never produced B-frames, only I- and P-frames.

  I created a standalone utility based on the ffmpeg source code and examples to test my encoder setup. It reads in an H.264 file, re-encodes the decoded frames, and outputs the result to a file using the ITU H.264 Annex B format. I also used ffmpeg to perform the same operation so I could compare against a known good implementation. My utility never outputs B-frames whereas ffmpeg does.

  I have since tried to figure out what ffmpeg does that my code doesn't. I first tried manually specifying encoder settings related to B-frames. This had no effect.

  I then tried running both ffmpeg and my utility under gdb and comparing the contents of the AVStream, AVCodecContext, and X264Context prior to opening the encoder and manually setting any fields that appeared different. Even with identical settings, I still only produce I- and P-frames.

  Finally, I thought that perhaps the problem was with my timestamp handling. I reworked my test utility to mimic the pipeline used by ffmpeg and to output timestamp debugging output like ffmpeg does. Even with my timestamps identical to ffmpeg's I still get no B-frames.

  At this point I don't know what else to try. When I run ffmpeg, I run it with the command line below. Note that aside from the "superfast" preset, I pretty much use the default values.

  ffmpeg -v debug -i ~/annexb.264 -codec:v libx264 -preset superfast -g 30 -f h264 ./out.264

  The code that configures the encoder is listed below. It specifies the "superfast" preset too.

  static AVStream *add_video_stream(AVFormatContext *output_ctx, AVCodec **output_codec, enum AVCodecID codec_id)
  
  {
  
      *output_codec = avcodec_find_encoder(codec_id);
  
      if (*output_codec == NULL) {
  
          printf("Could not find encoder for '%s' (%d)\n", avcodec_get_name(codec_id), codec_id);
  
          return NULL;
  
      }
  
  
  
      AVStream *output_stream = avformat_new_stream(output_ctx, *output_codec);
  
      if (output_stream == NULL) {
  
          printf("Could not create video stream.\n");
  
          return NULL;
  
      }
  
      output_stream->id = output_ctx->nb_streams - 1;
  
      AVCodecContext *codec_ctx = output_stream->codec;
  
  
  
      avcodec_get_context_defaults3(codec_ctx, *output_codec);
  
  
  
      codec_ctx->width = 1280;
  
      codec_ctx->height = 720;
  
  
  
      codec_ctx->time_base.den = 15000;
  
      codec_ctx->time_base.num = 1001;
  
  
  
  /*    codec_ctx->gop_size = 30;*/
  
      codec_ctx->pix_fmt = AV_PIX_FMT_YUVJ420P;
  
  
  
      // try to force B-frame output
  
  /*    codec_ctx->max_b_frames = 3;*/
  
  /*    codec_ctx->b_frame_strategy = 2;*/
  
  
  
      output_stream->sample_aspect_ratio.num = 1;
  
      output_stream->sample_aspect_ratio.den = 1;
  
  
  
      codec_ctx->sample_aspect_ratio.num = 1;
  
      codec_ctx->sample_aspect_ratio.den = 1;
  
  
  
      codec_ctx->chroma_sample_location = AVCHROMA_LOC_LEFT;
  
  
  
      codec_ctx->bits_per_raw_sample = 8;
  
  
  
      if ((output_ctx->oformat->flags & AVFMT_GLOBALHEADER) != 0) {
  
          codec_ctx->flags |= CODEC_FLAG_GLOBAL_HEADER;
  
      }
  
  
  
      return output_stream;
  
  }
  
  
  
  
  
  int main(int argc, char **argv)
  
  {
  
      // ... open input file 
  
  
  
      avformat_alloc_output_context2(&output_ctx, NULL, "h264", output_path);
  
      if (output_ctx == NULL) {
  
          fprintf(stderr, "Unable to allocate output context.\n");
  
          return 1;
  
      } 
  
  
  
      AVCodec *output_codec = NULL;
  
      output_stream = add_video_stream(output_ctx, &output_codec, output_ctx->oformat->video_codec);
  
      if (output_stream == NULL) {
  
          fprintf(stderr, "Error adding video stream to output context.\n");
  
          return 1;
  
      }
  
      encode_ctx = output_stream->codec;
  
  
  
      // seems to have no effect
  
  #if 0
  
      if (decode_ctx->extradata_size != 0) {
  
          size_t extradata_size = decode_ctx->extradata_size;
  
          printf("extradata_size: %zu\n", extradata_size);
  
          encode_ctx->extradata = av_mallocz(extradata_size + FF_INPUT_BUFFER_PADDING_SIZE);
  
          memcpy(encode_ctx->extradata, decode_ctx->extradata, extradata_size);
  
          encode_ctx->extradata_size = extradata_size;
  
      }
  
  #endif // 0
  
  
  
      AVDictionary *opts = NULL;
  
      av_dict_set(&opts, "preset", "superfast", 0);
  
      // av_dict_set(&opts, "threads", "auto", 0); // seems to have no effect
  
  
  
      ret = avcodec_open2(encode_ctx, output_codec, &opts);
  
      if (ret < 0) {
  
          fprintf(stderr, "Unable to open output video cocec: %s\n", av_err2str(ret));
  
          return 1;
  
      }
  
  
  
      // ... decoding/encoding loop, clean up, etc.
  
  
  
      return 0;
  
  }

  My test utility produces the following debug output in which you can see there are no B-frames produced :

  [libx264 @ 0x1b8c9c0] using mv_range_thread = 56
  
  [libx264 @ 0x1b8c9c0] using SAR=1/1
  
  [libx264 @ 0x1b8c9c0] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2 AVX
  
  [libx264 @ 0x1b8c9c0] profile High, level 3.1
  
  Output #0, h264, to './out.264':
  
      Stream #0:0, 0, 1/90000: Video: h264, yuvj420p, 1280x720 [SAR 1:1 DAR 16:9], 1001/15000, q=-1--1, 90k tbn, 14.99 tbc
  
  
  
  <snip>
  
  
  
  [libx264 @ 0x1b8c9c0] frame=   0 QP=17.22 NAL=3 Slice:I Poc:0   I:3600 P:0    SKIP:0    size=122837 bytes
  
  [libx264 @ 0x1b8c9c0] frame=   1 QP=18.03 NAL=2 Slice:P Poc:2   I:411  P:1825 SKIP:1364 size=25863 bytes
  
  [libx264 @ 0x1b8c9c0] frame=   2 QP=17.03 NAL=2 Slice:P Poc:4   I:369  P:2159 SKIP:1072 size=37880 bytes
  
  [libx264 @ 0x1b8c9c0] frame=   3 QP=16.90 NAL=2 Slice:P Poc:6   I:498  P:2330 SKIP:772  size=50509 bytes
  
  [libx264 @ 0x1b8c9c0] frame=   4 QP=16.68 NAL=2 Slice:P Poc:8   I:504  P:2233 SKIP:863  size=50791 bytes
  
  [libx264 @ 0x1b8c9c0] frame=   5 QP=16.52 NAL=2 Slice:P Poc:10  I:513  P:2286 SKIP:801  size=51820 bytes
  
  [libx264 @ 0x1b8c9c0] frame=   6 QP=16.49 NAL=2 Slice:P Poc:12  I:461  P:2293 SKIP:846  size=51311 bytes
  
  [libx264 @ 0x1b8c9c0] frame=   7 QP=16.65 NAL=2 Slice:P Poc:14  I:476  P:2287 SKIP:837  size=51196 bytes
  
  [libx264 @ 0x1b8c9c0] frame=   8 QP=16.66 NAL=2 Slice:P Poc:16  I:508  P:2240 SKIP:852  size=51577 bytes
  
  [libx264 @ 0x1b8c9c0] frame=   9 QP=16.55 NAL=2 Slice:P Poc:18  I:477  P:2278 SKIP:845  size=51531 bytes
  
  [libx264 @ 0x1b8c9c0] frame=  10 QP=16.67 NAL=2 Slice:P Poc:20  I:517  P:2233 SKIP:850  size=51946 bytes
  
  
  
  <snip>
  
  
  
  [libx264 @ 0x1b8c9c0] frame I:7     Avg QP:13.71  size:152207
  
  [libx264 @ 0x1b8c9c0] frame P:190   Avg QP:16.66  size: 50949
  
  [libx264 @ 0x1b8c9c0] mb I  I16..4: 27.1% 30.8% 42.1%
  
  [libx264 @ 0x1b8c9c0] mb P  I16..4:  6.8%  6.0%  0.8%  P16..4: 61.8%  0.0%  0.0%  0.0%  0.0%    skip:24.7%
  
  [libx264 @ 0x1b8c9c0] 8x8 transform intra:41.2% inter:86.9%
  
  [libx264 @ 0x1b8c9c0] coded y,uvDC,uvAC intra: 92.2% 28.3% 5.4% inter: 50.3% 1.9% 0.0%
  
  [libx264 @ 0x1b8c9c0] i16 v,h,dc,p:  7%  7% 77%  8%
  
  [libx264 @ 0x1b8c9c0] i8 v,h,dc,ddl,ddr,vr,hd,vl,hu:  7% 15% 49%  6%  4%  3%  5%  3%  8%
  
  [libx264 @ 0x1b8c9c0] i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 19% 25% 24%  6%  7%  4%  6%  3%  6%
  
  [libx264 @ 0x1b8c9c0] i8c dc,h,v,p: 72% 14% 10%  4%
  
  [libx264 @ 0x1b8c9c0] Weighted P-Frames: Y:0.0% UV:0.0%
  
  [libx264 @ 0x1b8c9c0] kb/s:6539.11
  
  </snip></snip>

  ffmpeg, on the other hand, produces the following output that is almost identical but includes B-frames :

  [libx264 @ 0x20b9c40] using mv_range_thread = 56
  
  [libx264 @ 0x20b9c40] using SAR=1/1
  
  [libx264 @ 0x20b9c40] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2 AVX
  
  [libx264 @ 0x20b9c40] profile High, level 3.1
  
  [h264 @ 0x20b8160] detected 4 logical cores
  
  Output #0, h264, to './out.264':
  
    Metadata:
  
      encoder         : Lavf54.63.104
  
      Stream #0:0, 0, 1/90000: Video: h264, yuvj420p, 1280x720 [SAR 1:1 DAR 16:9], 1001/15000, q=-1--1, 90k tbn, 14.99 tbc
  
  Stream mapping:
  
    Stream #0:0 -> #0:0 (h264 -> libx264)
  
  
  
  <snip>
  
  
  
  [libx264 @ 0x20b9c40] frame=   0 QP=17.22 NAL=3 Slice:I Poc:0   I:3600 P:0    SKIP:0    size=122835 bytes
  
  [libx264 @ 0x20b9c40] frame=   1 QP=18.75 NAL=2 Slice:P Poc:8   I:984  P:2045 SKIP:571  size=54208 bytes
  
  [libx264 @ 0x20b9c40] frame=   2 QP=19.40 NAL=2 Slice:B Poc:4   I:447  P:1581 SKIP:1572 size=24930 bytes
  
  [libx264 @ 0x20b9c40] frame=   3 QP=19.78 NAL=0 Slice:B Poc:2   I:199  P:1002 SKIP:2399 size=10717 bytes
  
  [libx264 @ 0x20b9c40] frame=   4 QP=20.19 NAL=0 Slice:B Poc:6   I:204  P:1155 SKIP:2241 size=15937 bytes
  
  [libx264 @ 0x20b9c40] frame=   5 QP=18.11 NAL=2 Slice:P Poc:16  I:990  P:2221 SKIP:389  size=64240 bytes
  
  [libx264 @ 0x20b9c40] frame=   6 QP=19.35 NAL=2 Slice:B Poc:12  I:439  P:1784 SKIP:1377 size=34048 bytes
  
  [libx264 @ 0x20b9c40] frame=   7 QP=19.88 NAL=0 Slice:B Poc:10  I:275  P:1035 SKIP:2290 size=16911 bytes
  
  [libx264 @ 0x20b9c40] frame=   8 QP=19.91 NAL=0 Slice:B Poc:14  I:257  P:1270 SKIP:2073 size=19172 bytes
  
  [libx264 @ 0x20b9c40] frame=   9 QP=17.90 NAL=2 Slice:P Poc:24  I:962  P:2204 SKIP:434  size=67439 bytes
  
  [libx264 @ 0x20b9c40] frame=  10 QP=18.84 NAL=2 Slice:B Poc:20  I:474  P:1911 SKIP:1215 size=37742 bytes
  
  
  
  <snip>
  
  
  
  [libx264 @ 0x20b9c40] frame I:7     Avg QP:15.95  size:130124
  
  [libx264 @ 0x20b9c40] frame P:52    Avg QP:17.78  size: 64787
  
  [libx264 @ 0x20b9c40] frame B:138   Avg QP:19.32  size: 26231
  
  [libx264 @ 0x20b9c40] consecutive B-frames:  6.6%  0.0%  0.0% 93.4%
  
  [libx264 @ 0x20b9c40] mb I  I16..4: 30.2% 35.2% 34.6%
  
  [libx264 @ 0x20b9c40] mb P  I16..4: 13.9% 11.4%  0.3%  P16..4: 60.4%  0.0%  0.0%  0.0%  0.0%    skip:13.9%
  
  [libx264 @ 0x20b9c40] mb B  I16..4:  5.7%  3.3%  0.0%  B16..8: 15.8%  0.0%  0.0%  direct:25.7%  skip:49.5%  L0:43.2% L1:37.3% BI:19.5%
  
  [libx264 @ 0x20b9c40] 8x8 transform intra:39.4% inter:77.2%
  
  [libx264 @ 0x20b9c40] coded y,uvDC,uvAC intra: 90.7% 26.6% 3.0% inter: 34.0% 4.1% 0.0%
  
  [libx264 @ 0x20b9c40] i16 v,h,dc,p:  7%  7% 77%  9%
  
  [libx264 @ 0x20b9c40] i8 v,h,dc,ddl,ddr,vr,hd,vl,hu:  7% 16% 51%  5%  4%  3%  5%  3%  7%
  
  [libx264 @ 0x20b9c40] i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 22% 27% 20%  6%  6%  3%  6%  3%  6%
  
  [libx264 @ 0x20b9c40] i8c dc,h,v,p: 71% 15% 11%  3%
  
  [libx264 @ 0x20b9c40] Weighted P-Frames: Y:0.0% UV:0.0%
  
  [libx264 @ 0x20b9c40] kb/s:4807.16
  
  </snip></snip>

  I'm sure I'm missing something simple, but I can't for the life of me see what it is. Any assistance would be greatly appreciated.

• libavcodec/libx264 do not produce B-frames

  6 novembre 2013, par Rob Schmidt

  I am writing an application in C++ that uses libavcodec with libx264 to encode video. However, the encoded data ended up being much larger than I expected. I analyzed the results and discovered that my encoding never produced B-frames, only I- and P-frames.

  I created a standalone utility based on the ffmpeg source code and examples to test my encoder setup. It reads in an H.264 file, re-encodes the decoded frames, and outputs the result to a file using the ITU H.264 Annex B format. I also used ffmpeg to perform the same operation so I could compare against a known good implementation. My utility never outputs B-frames whereas ffmpeg does.

  I have since tried to figure out what ffmpeg does that my code doesn’t. I first tried manually specifying encoder settings related to B-frames. This had no effect.

  I then tried running both ffmpeg and my utility under gdb and comparing the contents of the AVStream, AVCodecContext, and X264Context prior to opening the encoder and manually setting any fields that appeared different. Even with identical settings, I still only produce I- and P-frames.

  Finally, I thought that perhaps the problem was with my timestamp handling. I reworked my test utility to mimic the pipeline used by ffmpeg and to output timestamp debugging output like ffmpeg does. Even with my timestamps identical to ffmpeg’s I still get no B-frames.

  At this point I don’t know what else to try. When I run ffmpeg, I run it with the command line below. Note that aside from the "superfast" preset, I pretty much use the default values.

  ffmpeg -v debug -i ~/annexb.264 -codec:v libx264 -preset superfast -g 30 -f h264 ./out.264

  The code that configures the encoder is listed below. It specifies the "superfast" preset too.

  static AVStream *add_video_stream(AVFormatContext *output_ctx, AVCodec **output_codec, enum AVCodecID codec_id)
  
  {
  
      *output_codec = avcodec_find_encoder(codec_id);
  
      if (*output_codec == NULL) {
  
          printf("Could not find encoder for '%s' (%d)\n", avcodec_get_name(codec_id), codec_id);
  
          return NULL;
  
      }
  
  
  
      AVStream *output_stream = avformat_new_stream(output_ctx, *output_codec);
  
      if (output_stream == NULL) {
  
          printf("Could not create video stream.\n");
  
          return NULL;
  
      }
  
      output_stream->id = output_ctx->nb_streams - 1;
  
      AVCodecContext *codec_ctx = output_stream->codec;
  
  
  
      avcodec_get_context_defaults3(codec_ctx, *output_codec);
  
  
  
      codec_ctx->width = 1280;
  
      codec_ctx->height = 720;
  
  
  
      codec_ctx->time_base.den = 15000;
  
      codec_ctx->time_base.num = 1001;
  
  
  
  /*    codec_ctx->gop_size = 30;*/
  
      codec_ctx->pix_fmt = AV_PIX_FMT_YUVJ420P;
  
  
  
      // try to force B-frame output
  
  /*    codec_ctx->max_b_frames = 3;*/
  
  /*    codec_ctx->b_frame_strategy = 2;*/
  
  
  
      output_stream->sample_aspect_ratio.num = 1;
  
      output_stream->sample_aspect_ratio.den = 1;
  
  
  
      codec_ctx->sample_aspect_ratio.num = 1;
  
      codec_ctx->sample_aspect_ratio.den = 1;
  
  
  
      codec_ctx->chroma_sample_location = AVCHROMA_LOC_LEFT;
  
  
  
      codec_ctx->bits_per_raw_sample = 8;
  
  
  
      if ((output_ctx->oformat->flags & AVFMT_GLOBALHEADER) != 0) {
  
          codec_ctx->flags |= CODEC_FLAG_GLOBAL_HEADER;
  
      }
  
  
  
      return output_stream;
  
  }
  
  
  
  
  
  int main(int argc, char **argv)
  
  {
  
      // ... open input file 
  
  
  
      avformat_alloc_output_context2(&output_ctx, NULL, "h264", output_path);
  
      if (output_ctx == NULL) {
  
          fprintf(stderr, "Unable to allocate output context.\n");
  
          return 1;
  
      } 
  
  
  
      AVCodec *output_codec = NULL;
  
      output_stream = add_video_stream(output_ctx, &output_codec, output_ctx->oformat->video_codec);
  
      if (output_stream == NULL) {
  
          fprintf(stderr, "Error adding video stream to output context.\n");
  
          return 1;
  
      }
  
      encode_ctx = output_stream->codec;
  
  
  
      // seems to have no effect
  
  #if 0
  
      if (decode_ctx->extradata_size != 0) {
  
          size_t extradata_size = decode_ctx->extradata_size;
  
          printf("extradata_size: %zu\n", extradata_size);
  
          encode_ctx->extradata = av_mallocz(extradata_size + FF_INPUT_BUFFER_PADDING_SIZE);
  
          memcpy(encode_ctx->extradata, decode_ctx->extradata, extradata_size);
  
          encode_ctx->extradata_size = extradata_size;
  
      }
  
  #endif // 0
  
  
  
      AVDictionary *opts = NULL;
  
      av_dict_set(&opts, "preset", "superfast", 0);
  
      // av_dict_set(&opts, "threads", "auto", 0); // seems to have no effect
  
  
  
      ret = avcodec_open2(encode_ctx, output_codec, &opts);
  
      if (ret < 0) {
  
          fprintf(stderr, "Unable to open output video cocec: %s\n", av_err2str(ret));
  
          return 1;
  
      }
  
  
  
      // ... decoding/encoding loop, clean up, etc.
  
  
  
      return 0;
  
  }

  My test utility produces the following debug output in which you can see there are no B-frames produced :

  [libx264 @ 0x1b8c9c0] using mv_range_thread = 56
  
  [libx264 @ 0x1b8c9c0] using SAR=1/1
  
  [libx264 @ 0x1b8c9c0] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2 AVX
  
  [libx264 @ 0x1b8c9c0] profile High, level 3.1
  
  Output #0, h264, to './out.264':
  
      Stream #0:0, 0, 1/90000: Video: h264, yuvj420p, 1280x720 [SAR 1:1 DAR 16:9], 1001/15000, q=-1--1, 90k tbn, 14.99 tbc
  
  
  
  <snip>
  
  
  
  [libx264 @ 0x1b8c9c0] frame=   0 QP=17.22 NAL=3 Slice:I Poc:0   I:3600 P:0    SKIP:0    size=122837 bytes
  
  [libx264 @ 0x1b8c9c0] frame=   1 QP=18.03 NAL=2 Slice:P Poc:2   I:411  P:1825 SKIP:1364 size=25863 bytes
  
  [libx264 @ 0x1b8c9c0] frame=   2 QP=17.03 NAL=2 Slice:P Poc:4   I:369  P:2159 SKIP:1072 size=37880 bytes
  
  [libx264 @ 0x1b8c9c0] frame=   3 QP=16.90 NAL=2 Slice:P Poc:6   I:498  P:2330 SKIP:772  size=50509 bytes
  
  [libx264 @ 0x1b8c9c0] frame=   4 QP=16.68 NAL=2 Slice:P Poc:8   I:504  P:2233 SKIP:863  size=50791 bytes
  
  [libx264 @ 0x1b8c9c0] frame=   5 QP=16.52 NAL=2 Slice:P Poc:10  I:513  P:2286 SKIP:801  size=51820 bytes
  
  [libx264 @ 0x1b8c9c0] frame=   6 QP=16.49 NAL=2 Slice:P Poc:12  I:461  P:2293 SKIP:846  size=51311 bytes
  
  [libx264 @ 0x1b8c9c0] frame=   7 QP=16.65 NAL=2 Slice:P Poc:14  I:476  P:2287 SKIP:837  size=51196 bytes
  
  [libx264 @ 0x1b8c9c0] frame=   8 QP=16.66 NAL=2 Slice:P Poc:16  I:508  P:2240 SKIP:852  size=51577 bytes
  
  [libx264 @ 0x1b8c9c0] frame=   9 QP=16.55 NAL=2 Slice:P Poc:18  I:477  P:2278 SKIP:845  size=51531 bytes
  
  [libx264 @ 0x1b8c9c0] frame=  10 QP=16.67 NAL=2 Slice:P Poc:20  I:517  P:2233 SKIP:850  size=51946 bytes
  
  
  
  <snip>
  
  
  
  [libx264 @ 0x1b8c9c0] frame I:7     Avg QP:13.71  size:152207
  
  [libx264 @ 0x1b8c9c0] frame P:190   Avg QP:16.66  size: 50949
  
  [libx264 @ 0x1b8c9c0] mb I  I16..4: 27.1% 30.8% 42.1%
  
  [libx264 @ 0x1b8c9c0] mb P  I16..4:  6.8%  6.0%  0.8%  P16..4: 61.8%  0.0%  0.0%  0.0%  0.0%    skip:24.7%
  
  [libx264 @ 0x1b8c9c0] 8x8 transform intra:41.2% inter:86.9%
  
  [libx264 @ 0x1b8c9c0] coded y,uvDC,uvAC intra: 92.2% 28.3% 5.4% inter: 50.3% 1.9% 0.0%
  
  [libx264 @ 0x1b8c9c0] i16 v,h,dc,p:  7%  7% 77%  8%
  
  [libx264 @ 0x1b8c9c0] i8 v,h,dc,ddl,ddr,vr,hd,vl,hu:  7% 15% 49%  6%  4%  3%  5%  3%  8%
  
  [libx264 @ 0x1b8c9c0] i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 19% 25% 24%  6%  7%  4%  6%  3%  6%
  
  [libx264 @ 0x1b8c9c0] i8c dc,h,v,p: 72% 14% 10%  4%
  
  [libx264 @ 0x1b8c9c0] Weighted P-Frames: Y:0.0% UV:0.0%
  
  [libx264 @ 0x1b8c9c0] kb/s:6539.11
  
  </snip></snip>

  ffmpeg, on the other hand, produces the following output that is almost identical but includes B-frames :

  [libx264 @ 0x20b9c40] using mv_range_thread = 56
  
  [libx264 @ 0x20b9c40] using SAR=1/1
  
  [libx264 @ 0x20b9c40] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2 AVX
  
  [libx264 @ 0x20b9c40] profile High, level 3.1
  
  [h264 @ 0x20b8160] detected 4 logical cores
  
  Output #0, h264, to './out.264':
  
    Metadata:
  
      encoder         : Lavf54.63.104
  
      Stream #0:0, 0, 1/90000: Video: h264, yuvj420p, 1280x720 [SAR 1:1 DAR 16:9], 1001/15000, q=-1--1, 90k tbn, 14.99 tbc
  
  Stream mapping:
  
    Stream #0:0 -> #0:0 (h264 -> libx264)
  
  
  
  <snip>
  
  
  
  [libx264 @ 0x20b9c40] frame=   0 QP=17.22 NAL=3 Slice:I Poc:0   I:3600 P:0    SKIP:0    size=122835 bytes
  
  [libx264 @ 0x20b9c40] frame=   1 QP=18.75 NAL=2 Slice:P Poc:8   I:984  P:2045 SKIP:571  size=54208 bytes
  
  [libx264 @ 0x20b9c40] frame=   2 QP=19.40 NAL=2 Slice:B Poc:4   I:447  P:1581 SKIP:1572 size=24930 bytes
  
  [libx264 @ 0x20b9c40] frame=   3 QP=19.78 NAL=0 Slice:B Poc:2   I:199  P:1002 SKIP:2399 size=10717 bytes
  
  [libx264 @ 0x20b9c40] frame=   4 QP=20.19 NAL=0 Slice:B Poc:6   I:204  P:1155 SKIP:2241 size=15937 bytes
  
  [libx264 @ 0x20b9c40] frame=   5 QP=18.11 NAL=2 Slice:P Poc:16  I:990  P:2221 SKIP:389  size=64240 bytes
  
  [libx264 @ 0x20b9c40] frame=   6 QP=19.35 NAL=2 Slice:B Poc:12  I:439  P:1784 SKIP:1377 size=34048 bytes
  
  [libx264 @ 0x20b9c40] frame=   7 QP=19.88 NAL=0 Slice:B Poc:10  I:275  P:1035 SKIP:2290 size=16911 bytes
  
  [libx264 @ 0x20b9c40] frame=   8 QP=19.91 NAL=0 Slice:B Poc:14  I:257  P:1270 SKIP:2073 size=19172 bytes
  
  [libx264 @ 0x20b9c40] frame=   9 QP=17.90 NAL=2 Slice:P Poc:24  I:962  P:2204 SKIP:434  size=67439 bytes
  
  [libx264 @ 0x20b9c40] frame=  10 QP=18.84 NAL=2 Slice:B Poc:20  I:474  P:1911 SKIP:1215 size=37742 bytes
  
  
  
  <snip>
  
  
  
  [libx264 @ 0x20b9c40] frame I:7     Avg QP:15.95  size:130124
  
  [libx264 @ 0x20b9c40] frame P:52    Avg QP:17.78  size: 64787
  
  [libx264 @ 0x20b9c40] frame B:138   Avg QP:19.32  size: 26231
  
  [libx264 @ 0x20b9c40] consecutive B-frames:  6.6%  0.0%  0.0% 93.4%
  
  [libx264 @ 0x20b9c40] mb I  I16..4: 30.2% 35.2% 34.6%
  
  [libx264 @ 0x20b9c40] mb P  I16..4: 13.9% 11.4%  0.3%  P16..4: 60.4%  0.0%  0.0%  0.0%  0.0%    skip:13.9%
  
  [libx264 @ 0x20b9c40] mb B  I16..4:  5.7%  3.3%  0.0%  B16..8: 15.8%  0.0%  0.0%  direct:25.7%  skip:49.5%  L0:43.2% L1:37.3% BI:19.5%
  
  [libx264 @ 0x20b9c40] 8x8 transform intra:39.4% inter:77.2%
  
  [libx264 @ 0x20b9c40] coded y,uvDC,uvAC intra: 90.7% 26.6% 3.0% inter: 34.0% 4.1% 0.0%
  
  [libx264 @ 0x20b9c40] i16 v,h,dc,p:  7%  7% 77%  9%
  
  [libx264 @ 0x20b9c40] i8 v,h,dc,ddl,ddr,vr,hd,vl,hu:  7% 16% 51%  5%  4%  3%  5%  3%  7%
  
  [libx264 @ 0x20b9c40] i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 22% 27% 20%  6%  6%  3%  6%  3%  6%
  
  [libx264 @ 0x20b9c40] i8c dc,h,v,p: 71% 15% 11%  3%
  
  [libx264 @ 0x20b9c40] Weighted P-Frames: Y:0.0% UV:0.0%
  
  [libx264 @ 0x20b9c40] kb/s:4807.16
  
  </snip></snip>

  I’m sure I’m missing something simple, but I can’t for the life of me see what it is. Any assistance would be greatly appreciated.

• Prevent ffmpeg from changing the intensity of colors while downscaling the resolution of the video

  29 août 2022, par dravit

  I have a use case where I need to downscale a 716x1280 mp4 video to 358x640 (half of the original). Command that I used is

  


  ffmpeg -i ./input.mp4 -vf "scale=640:640:force_original_aspect_ratio=decrease,pad=ceil(iw/2)*2:ceil(ih/2)*2" ./output.mp4


  


  Out of 10 sample videos, 2 of the them suffered impact on colors. Below I have attached a comparison from the one which was impacted the most.

  


  

  


  NOTE : The one on the right is a frame from the original video and the frame on the left is the one from the processed (down scaled) video. Notice the colors red and green in the image (even the skin color and hair color were changed).

  


  What I am looking for is

  


  

  • Is there any way I can prevent changes like these happening ? Probably some flag on saturation, brightness, contrast or any other parameter.

  


  • I am assuming that ffmpeg uses some default settings while downscaling a video. What made ffmpeg change colors only for these two videos ? If it made similar changes for the rest of the videos as well, how to predict this behaviour before hand ?

  


  


  EDIT :

  


  What I already have Tried ?

  


  

  • -crf with values 0 and 18.

  


  • -preset veryslow as mentioned here

  


  


  None helped

  


  Mediainfo input V/S output

  


  





  


  


  


  


  


  



  


  


  


  


  


  


  


  


  


  


  


  


  


  


  


  


  


  


  


  


  


  


  


  


  


  param	input	output
  color range	Limited	NA (attribute not in description)
  color primaries	BT.2020	NA (attribute not in description)
  transfer characteristics	HLG	NA (attribute not in description)
  matrix coefficients	BT.2020 non-constant	NA (attribute not in description)
  bit deapth	8	8

  


  


  Logs of the ffmpeg command

  


  ffmpeg -i ./input.mp4 -vf "scale=640:640:force_original_aspect_ratio=decrease,pad=ceil(iw/2)*2:ceil(ih/2)*2" -movflags +faststart ./output.mp4
ffmpeg version 4.3.1 Copyright (c) 2000-2020 the FFmpeg developers
  built with Apple clang version 12.0.0 (clang-1200.0.32.28)
  configuration: --prefix=/usr/local/Cellar/ffmpeg/4.3.1_9 --enable-shared --enable-pthreads --enable-version3 --enable-avresample --cc=clang --host-cflags= --host-ldflags= --enable-ffplay --enable-gnutls --enable-gpl --enable-libaom --enable-libbluray --enable-libdav1d --enable-libmp3lame --enable-libopus --enable-librav1e --enable-librubberband --enable-libsnappy --enable-libsrt --enable-libtesseract --enable-libtheora --enable-libvidstab --enable-libvorbis --enable-libvpx --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxml2 --enable-libxvid --enable-lzma --enable-libfontconfig --enable-libfreetype --enable-frei0r --enable-libass --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-librtmp --enable-libspeex --enable-libsoxr --enable-videotoolbox --enable-libzmq --enable-libzimg --disable-libjack --disable-indev=jack
  libavutil      56. 51.100 / 56. 51.100
  libavcodec     58. 91.100 / 58. 91.100
  libavformat    58. 45.100 / 58. 45.100
  libavdevice    58. 10.100 / 58. 10.100
  libavfilter     7. 85.100 /  7. 85.100
  libavresample   4.  0.  0 /  4.  0.  0
  libswscale      5.  7.100 /  5.  7.100
  libswresample   3.  7.100 /  3.  7.100
  libpostproc    55.  7.100 / 55.  7.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from './input.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf58.45.100
  Duration: 00:00:30.05, start: 0.000000, bitrate: 10366 kb/s
    Stream #0:0(und): Video: h264 (Main) (avc1 / 0x31637661), yuv420p(tv, bt2020nc/bt2020/arib-std-b67), 716x1280, 10116 kb/s, 30 fps, 30 tbr, 19200 tbn, 38400 tbc (default)
    Metadata:
      handler_name    : Core Media Video
    Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 245 kb/s (default)
    Metadata:
      handler_name    : Core Media Audio
Stream mapping:
  Stream #0:0 -> #0:0 (h264 (native) -> h264 (libx264))
  Stream #0:1 -> #0:1 (aac (native) -> aac (native))
Press [q] to stop, [?] for help
[libx264 @ 0x7faab4808800] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2 AVX FMA3 BMI2 AVX2
[libx264 @ 0x7faab4808800] profile High, level 3.0, 4:2:0, 8-bit
[libx264 @ 0x7faab4808800] 264 - core 161 r3027 4121277 - H.264/MPEG-4 AVC codec - Copyleft 2003-2020 - http://www.videolan.org/x264.html - options: cabac=1 ref=3 deblock=1:0:0 analyse=0x3:0x113 me=hex subme=7 psy=1 psy_rd=1.00:0.00 mixed_ref=1 me_range=16 chroma_me=1 trellis=1 8x8dct=1 cqm=0 deadzone=21,11 fast_pskip=1 chroma_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 scenecut=40 intra_refresh=0 rc_lookahead=40 rc=crf mbtree=1 crf=23.0 qcomp=0.60 qpmin=0 qpmax=69 qpstep=4 ip_ratio=1.40 aq=1:1.00
Output #0, mp4, to './output.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf58.45.100
    Stream #0:0(und): Video: h264 (libx264) (avc1 / 0x31637661), yuv420p, 358x640, q=-1--1, 30 fps, 15360 tbn, 30 tbc (default)
    Metadata:
      handler_name    : Core Media Video
      encoder         : Lavc58.91.100 libx264
    Side data:
      cpb: bitrate max/min/avg: 0/0/0 buffer size: 0 vbv_delay: N/A
    Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 128 kb/s (default)
    Metadata:
      handler_name    : Core Media Audio
      encoder         : Lavc58.91.100 aac
[mp4 @ 0x7faab5808800] Starting second pass: moving the moov atom to the beginning of the file
frame=  901 fps=210 q=-1.0 Lsize=    3438kB time=00:00:30.02 bitrate= 938.0kbits/s speed=7.01x
video:2933kB audio:472kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.974633%
[libx264 @ 0x7faab4808800] frame I:6     Avg QP:22.60  size: 20769
[libx264 @ 0x7faab4808800] frame P:228   Avg QP:24.84  size:  7657
[libx264 @ 0x7faab4808800] frame B:667   Avg QP:27.59  size:  1697
[libx264 @ 0x7faab4808800] consecutive B-frames:  0.9%  0.9%  1.0% 97.2%
[libx264 @ 0x7faab4808800] mb I  I16..4:  9.5% 64.6% 26.0%
[libx264 @ 0x7faab4808800] mb P  I16..4:  2.5% 12.2%  2.5%  P16..4: 37.2% 20.6% 11.2%  0.0%  0.0%    skip:13.7%
[libx264 @ 0x7faab4808800] mb B  I16..4:  0.4%  2.1%  0.2%  B16..8: 42.2%  7.1%  1.2%  direct: 1.8%  skip:44.9%  L0:39.4% L1:52.8% BI: 7.8%
[libx264 @ 0x7faab4808800] 8x8 transform intra:72.2% inter:74.2%
[libx264 @ 0x7faab4808800] coded y,uvDC,uvAC intra: 61.8% 67.2% 20.2% inter: 16.7% 13.9% 1.3%
[libx264 @ 0x7faab4808800] i16 v,h,dc,p: 24% 19%  7% 50%
[libx264 @ 0x7faab4808800] i8 v,h,dc,ddl,ddr,vr,hd,vl,hu: 21% 16% 15%  6%  9% 11%  7% 10%  6%
[libx264 @ 0x7faab4808800] i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 25% 16% 13%  7%  9% 10%  7%  9%  4%
[libx264 @ 0x7faab4808800] i8c dc,h,v,p: 53% 16% 26%  5%
[libx264 @ 0x7faab4808800] Weighted P-Frames: Y:3.9% UV:1.8%
[libx264 @ 0x7faab4808800] ref P L0: 57.8% 19.5% 14.8%  7.8%  0.1%
[libx264 @ 0x7faab4808800] ref B L0: 90.7%  7.2%  2.1%
[libx264 @ 0x7faab4808800] ref B L1: 95.3%  4.7%
[libx264 @ 0x7faab4808800] kb/s:799.80
[aac @ 0x7faab2036a00] Qavg: 189.523