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• Why motion vector extracted from b frames are unchange ?

  19 août 2019, par 霍宇琦

  I am writing c codes to extract motion vectors from b frame in MPEG4(Part2) compressed video format. But some motion vector seems wrong.

  I use a raw video clips, using the extract_mvs.c from ffmpeg 4.2. For example if the frame seq is IPBPPBPP.... i can get all the side data for all frame. But when inspecting the mv->src_x, mv->src_y, mv->dst_x, mv->dst_y i find that all the srcs are equal to dsts for some individual frames, there must be sth wrong in it, but i change little from the official code.

  //modify from ffmpeg/doc/example/extract_mvs.c:
  
  
  
  while(getting frames one by one) {
  
      AVFrameSideData *sd;
  
      video_frame_count++;
  
  
  
      //printf("%d", video_frame_count);
  
      if(video_frame_count < 19){
  
          if (frame->pict_type == AV_PICTURE_TYPE_I ) printf("\nI");
  
          if (frame->pict_type == AV_PICTURE_TYPE_B ) printf("B"); 
  
          if (frame->pict_type == AV_PICTURE_TYPE_P ) printf("P");
  
  
  
          sd = av_frame_get_side_data(frame, AV_FRAME_DATA_MOTION_VECTORS);
  
          if (sd) {
  
              const AVMotionVector *mvs = (const AVMotionVector *)sd->data;
  
              for (i = 0; i < sd->size / sizeof(*mvs); i++) {
  
                  const AVMotionVector *mv = &mvs[i];
  
                  if (mv->dst_x - mv->src_x != 0 || mv->dst_y - mv->src_y != 0) {
  
                  printf("%d,%2d,%2d,%2d,%4d,%4d,%4d,%4d,0x%"PRIx64"\n",
  
                      video_frame_count, mv->source,
  
                      mv->w, mv->h, mv->src_x, mv->src_y,
  
                      mv->dst_x, mv->dst_y, mv->flags);
  
                      break;
  
                  }
  
              }
  
          }
  
          av_frame_unref(frame);
  
      }
  
  }

  Outputs are :

  Input #0, avi, from 'origin.avi':
  
    Duration: 00:00:13.63, start: 0.000000, bitrate: 492 kb/s
  
      Stream #0:0: Video: mpeg4 (DX50 / 0x30355844), yuv420p, 320x240 [SAR 1:1 DAR 4:3], 486 kb/s, 30 fps, 30 tbr, 30 tbn, 30k tbc
  
      Metadata:
  
        title           : H:\HumanActionDB\MotionClips\hmdb51_30fps_wBrd_10off_divx\brush_??
  
  framenum,source,blockw,blockh,srcx,srcy,dstx,dsty,flags
  
  
  
  [mpeg4 @ 0x55739dc29580] Video uses a non-standard and wasteful way to store B-frames ('packed B-frames'). Consider using the mpeg4_unpack_bframes bitstream filter without encoding but stream copy to fix it.
  
  IP2,-1,16,16, 137,  24, 136,  24,0x0
  
  BP4,-1,16,16, 152,  57, 152,  56,0x0
  
  P5,-1,16,16,  56, 155,  56, 152,0x0
  
  BP7,-1,16,16, 151,  40, 152,  40,0x0
  
  PB9,-1,16,16, 151,  40, 152,  40,0x0
  
  P10,-1,16,16, 152,  39, 152,  40,0x0
  
  P11,-1,16,16,  26,  55,  24,  56,0x0
  
  B12,-1,16,16, 152,  39, 152,  40,0x0
  
  P13,-1,16,16, 152,  39, 152,  40,0x0
  
  P14,-1,16,16,  41, 168,  40, 168,0x0
  
  B15,-1,16,16, 152,  39, 152,  40,0x0
  
  P16,-1,16,16, 153,  39, 152,  40,0x0
  
  PB18,-1,16,16, 168,  55, 168,  56,0x0

  you can see that the third frame(B) and the sixth, eighth frame(B, P) and the 17th frame (P) can be read, and the data can be extract from them, but

  mv->dst_x == mv->src_x && mv->dst_y - mv->src_y

  Can someone help me ? Thanks.

• Android FFMPEG Build with librtmp

  20 décembre 2013, par Dan Turner

  I have been pulling my hair out trying to compile FFMPEG for Android with librtmp enabled. I have successfully built FFMPEG using the Guardian Project here, but it doesn't have librtmp support. The only answer I have found to this issue is on a previous Stack Overflow question (HERE), but it doesn't want to work for me.

  At the moment, I have the cross-compiled librtmp.so.0 file from the official rtmpdump android build in an rtmpdump/librtmp folder sitting in the android-ffmpeg folder. An extract from my configure_ffmpeg.sh file reads as follows :

  ./configure \
  
  $DEBUG_FLAG \
  
  --arch=arm \
  
  --cpu=cortex-a8 \
  
  --target-os=linux \
  
  --enable-runtime-cpudetect \
  
  --prefix=$prefix \
  
  --enable-pic \
  
  --disable-shared \
  
  --enable-static \
  
  --cross-prefix=$NDK_TOOLCHAIN_BASE/bin/$NDK_ABI-linux-androideabi- \
  
  --sysroot="$NDK_SYSROOT" \
  
  --extra-cflags="-I../x264 -mfloat-abi=softfp -mfpu=neon" \
  
  --extra-ldflags="-L../x264" \
  
  --extra-cflags="-I/home/dan/android-ffmpeg/rtmpdump" \
  
  --extra-ldflags="-L/home/dan/android-ffmpeg/rtmpdump -lrtmp"
  
  \
  
  
  
  --enable-version3 \
  
  --enable-gpl \
  
  \
  
  --disable-doc \
  
  --enable-yasm \
  
  \
  
  --enable-decoders \
  
  --enable-encoders \
  
  --enable-muxers \
  
  --enable-demuxers \
  
  --enable-parsers \
  
  --enable-protocols \
  
  --enable-filters \
  
  --enable-avresample \
  
  --enable-libfreetype \
  
  \
  
  --disable-indevs \
  
  --enable-indev=lavfi \
  
  --disable-outdevs \
  
  \
  
  --enable-hwaccels \
  
  \
  
  --enable-ffmpeg \
  
  --disable-ffplay \
  
  --disable-ffprobe \
  
  --enable-ffserver \
  
  --enable-network \
  
  \
  
  --enable-libx264 \
  
  --enable-zlib \
  
  --enable-librtmp \

  When I try to compile this, it eventually displays an error and my FFMPEG config.log file tells me that it can't find -lrtmp. I'm positive I'm directing it to the right directory... does anyone have any ideas ?

  Regards

  Dan

• Anomalie #2381 : Corriger le niveau d’intertitre

  9 juin 2018, par b b

  Il y a des H2 dans la dist, qui introduisent des listes d’articles, de résultats, ou des blocs (forum), je pense qu’ils peuvent rester comme ça.

  Si le bloc de forum sous le texte de l’article reste en h2, il va se retrouver "au même niveau" qu’un intertitre en h2 donc, c’est pas top non ?