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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 &#39;./out.264&#39;:
     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 &amp; 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(&amp;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, &amp;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(&amp;opts, "preset", "superfast", 0);
       // av_dict_set(&amp;opts, "threads", "auto", 0); // seems to have no effect

       ret = avcodec_open2(encode_ctx, output_codec, &amp;opts);
       if (ret &lt; 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

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

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    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.

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    Comparison of frames from the most impacted video

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    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).

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    What I am looking for is

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

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    What I already have Tried ?

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    • -crf with values 0 and 18.
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    • -preset veryslow as mentioned here
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    None helped

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    Mediainfo input V/S output

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    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

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    Logs of the ffmpeg command

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    ffmpeg -i ./input.mp4 -vf "scale=640:640:force_original_aspect_ratio=decrease,pad=ceil(iw/2)*2:ceil(ih/2)*2" -movflags &#x2B;faststart ./output.mp4&#xA;ffmpeg version 4.3.1 Copyright (c) 2000-2020 the FFmpeg developers&#xA;  built with Apple clang version 12.0.0 (clang-1200.0.32.28)&#xA;  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&#xA;  libavutil      56. 51.100 / 56. 51.100&#xA;  libavcodec     58. 91.100 / 58. 91.100&#xA;  libavformat    58. 45.100 / 58. 45.100&#xA;  libavdevice    58. 10.100 / 58. 10.100&#xA;  libavfilter     7. 85.100 /  7. 85.100&#xA;  libavresample   4.  0.  0 /  4.  0.  0&#xA;  libswscale      5.  7.100 /  5.  7.100&#xA;  libswresample   3.  7.100 /  3.  7.100&#xA;  libpostproc    55.  7.100 / 55.  7.100&#xA;Input #0, mov,mp4,m4a,3gp,3g2,mj2, from &#x27;./input.mp4&#x27;:&#xA;  Metadata:&#xA;    major_brand     : isom&#xA;    minor_version   : 512&#xA;    compatible_brands: isomiso2avc1mp41&#xA;    encoder         : Lavf58.45.100&#xA;  Duration: 00:00:30.05, start: 0.000000, bitrate: 10366 kb/s&#xA;    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)&#xA;    Metadata:&#xA;      handler_name    : Core Media Video&#xA;    Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 245 kb/s (default)&#xA;    Metadata:&#xA;      handler_name    : Core Media Audio&#xA;Stream mapping:&#xA;  Stream #0:0 -> #0:0 (h264 (native) -> h264 (libx264))&#xA;  Stream #0:1 -> #0:1 (aac (native) -> aac (native))&#xA;Press [q] to stop, [?] for help&#xA;[libx264 @ 0x7faab4808800] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2 AVX FMA3 BMI2 AVX2&#xA;[libx264 @ 0x7faab4808800] profile High, level 3.0, 4:2:0, 8-bit&#xA;[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&#xA;Output #0, mp4, to &#x27;./output.mp4&#x27;:&#xA;  Metadata:&#xA;    major_brand     : isom&#xA;    minor_version   : 512&#xA;    compatible_brands: isomiso2avc1mp41&#xA;    encoder         : Lavf58.45.100&#xA;    Stream #0:0(und): Video: h264 (libx264) (avc1 / 0x31637661), yuv420p, 358x640, q=-1--1, 30 fps, 15360 tbn, 30 tbc (default)&#xA;    Metadata:&#xA;      handler_name    : Core Media Video&#xA;      encoder         : Lavc58.91.100 libx264&#xA;    Side data:&#xA;      cpb: bitrate max/min/avg: 0/0/0 buffer size: 0 vbv_delay: N/A&#xA;    Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 128 kb/s (default)&#xA;    Metadata:&#xA;      handler_name    : Core Media Audio&#xA;      encoder         : Lavc58.91.100 aac&#xA;[mp4 @ 0x7faab5808800] Starting second pass: moving the moov atom to the beginning of the file&#xA;frame=  901 fps=210 q=-1.0 Lsize=    3438kB time=00:00:30.02 bitrate= 938.0kbits/s speed=7.01x&#xA;video:2933kB audio:472kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.974633%&#xA;[libx264 @ 0x7faab4808800] frame I:6     Avg QP:22.60  size: 20769&#xA;[libx264 @ 0x7faab4808800] frame P:228   Avg QP:24.84  size:  7657&#xA;[libx264 @ 0x7faab4808800] frame B:667   Avg QP:27.59  size:  1697&#xA;[libx264 @ 0x7faab4808800] consecutive B-frames:  0.9%  0.9%  1.0% 97.2%&#xA;[libx264 @ 0x7faab4808800] mb I  I16..4:  9.5% 64.6% 26.0%&#xA;[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%&#xA;[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%&#xA;[libx264 @ 0x7faab4808800] 8x8 transform intra:72.2% inter:74.2%&#xA;[libx264 @ 0x7faab4808800] coded y,uvDC,uvAC intra: 61.8% 67.2% 20.2% inter: 16.7% 13.9% 1.3%&#xA;[libx264 @ 0x7faab4808800] i16 v,h,dc,p: 24% 19%  7% 50%&#xA;[libx264 @ 0x7faab4808800] i8 v,h,dc,ddl,ddr,vr,hd,vl,hu: 21% 16% 15%  6%  9% 11%  7% 10%  6%&#xA;[libx264 @ 0x7faab4808800] i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 25% 16% 13%  7%  9% 10%  7%  9%  4%&#xA;[libx264 @ 0x7faab4808800] i8c dc,h,v,p: 53% 16% 26%  5%&#xA;[libx264 @ 0x7faab4808800] Weighted P-Frames: Y:3.9% UV:1.8%&#xA;[libx264 @ 0x7faab4808800] ref P L0: 57.8% 19.5% 14.8%  7.8%  0.1%&#xA;[libx264 @ 0x7faab4808800] ref B L0: 90.7%  7.2%  2.1%&#xA;[libx264 @ 0x7faab4808800] ref B L1: 95.3%  4.7%&#xA;[libx264 @ 0x7faab4808800] kb/s:799.80&#xA;[aac @ 0x7faab2036a00] Qavg: 189.523&#xA;

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