vp7: interlaced sample with "blit-pitch" feature

[ami_stuff]

so it eventually can be implemented

https://ffmpeg.org/pipermail/ffmpeg-devel/2014-February/154080.html

C:\>ffmpegx -i C:\interlaced_blit_pitch.avi out.avi
ffmpeg version N-80043-g1499242 Copyright (c) 2000-2016 the FFmpeg developers
  built with gcc 4.5.0 (GCC) 20100414 (Fedora MinGW 4.5.0-1.fc14)
  configuration: --prefix=/var/www/users/research/ffmpeg/snapshots/build --arch=
x86 --target-os=mingw32 --cross-prefix=i686-pc-mingw32- --cc='ccache i686-pc-min
gw32-gcc' --enable-pthreads --enable-memalign-hack --enable-runtime-cpudetect --
enable-cross-compile --enable-static --disable-shared --extra-libs='-lws2_32 -lw
inmm -lpthread' --extra-cflags='--static -I/var/www/users/research/ffmpeg/snapsh
ots/build/include' --extra-ldflags='-static -L/var/www/users/research/ffmpeg/sna
pshots/build/lib' --enable-bzlib --enable-zlib --enable-gpl --enable-version3 --
enable-nonfree --enable-libx264 --enable-libspeex --enable-libtheora --enable-li
bvorbis --enable-libfaac --enable-libxvid --enable-libopencore-amrnb --enable-li
bopencore-amrwb --enable-libmp3lame --enable-libfreetype --enable-libvpx --disab
le-decoder=libvpx
  libavutil      55. 24.100 / 55. 24.100
  libavcodec     57. 42.100 / 57. 42.100
  libavformat    57. 36.100 / 57. 36.100
  libavdevice    57.  0.101 / 57.  0.101
  libavfilter     6. 46.100 /  6. 46.100
  libswscale      4.  1.100 /  4.  1.100
  libswresample   2.  0.101 /  2.  0.101
  libpostproc    54.  0.100 / 54.  0.100
Input #0, avi, from 'C:\interlaced_blit_pitch.avi':
  Duration: 00:00:12.64, start: 0.000000, bitrate: 307 kb/s
    Stream #0:0: Video: vp7 (VP70 / 0x30375056), yuv420p, 320x240, 298 kb/s, 23.
97 fps, 23.97 tbr, 23.97 tbn
File 'out.avi' already exists. Overwrite ? [y/N] y
[avi @ 0x28c4c80] Using AVStream.codec to pass codec parameters to muxers is dep
recated, use AVStream.codecpar instead.
Output #0, avi, to 'out.avi':
  Metadata:
    ISFT            : Lavf57.36.100
    Stream #0:0: Video: mpeg4 (FMP4 / 0x34504D46), yuv420p, 320x240, q=2-31, 200
 kb/s, 23.97 fps, 23.97 tbn
    Metadata:
      encoder         : Lavc57.42.100 mpeg4
    Side data:
      cpb: bitrate max/min/avg: 0/0/200000 buffer size: 0 vbv_delay: -1
Stream mapping:
  Stream #0:0 -> #0:0 (vp7 (native) -> mpeg4 (native))
Press [q] to stop, [?] for help
[vp7 @ 0x2c59bc0] Feature blit-pitch present in macroblock (value 0x12)
    Last message repeated 87 times
frame=  303 fps=0.0 q=4.5 Lsize=     414kB time=00:00:12.64 bitrate= 268.0kbits/
s speed=26.1x
video:401kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing o
verhead: 3.192601%