[StvG]

Almost the same speed as "direct"

ffmpeg.exe -i 1.avs -c:v libx265 -preset ultrafast -x265-params ctu=32:pools=10:frame-threads=2 -f rawvideo - > x265.txt 2>&1

ffmpeg version 7211e1c Copyright (c) 2000-2019 the FFmpeg developers
  built with gcc 9.1.1 (GCC) 20190517
  configuration: --enable-libx265 --enable-avisynth --extra-cflags='-march=core-avx2 -mtune=native -pipe -s -O2' --cpu=core-avx2 --disable-debug --enable-gpl --cross-prefix=x86_64-w64-mingw32- --target-os=mingw32 --arch=x86_64 --pkg-config-flags=--static --enable-zlib --disable-pthreads --enable-w32threads --enable-version3
  libavutil      56. 22.100 / 56. 22.100
  libavcodec     58. 35.100 / 58. 35.100
  libavformat    58. 20.100 / 58. 20.100
  libavdevice    58.  5.100 / 58.  5.100
  libavfilter     7. 40.101 /  7. 40.101
  libswscale      5.  3.100 /  5.  3.100
  libswresample   3.  3.100 /  3.  3.100
  libpostproc    55.  3.100 / 55.  3.100
Input #0, avisynth, from '1.avs':
  Duration: 00:03:00.01, start: 0.000000, bitrate: 0 kb/s
    Stream #0:0: Video: rawvideo (Y3[11][10] / 0xA0B3359), yuv420p10le, 1920x1080, 23.98 fps, 23.98 tbr, 23.98 tbn, 23.98 tbc
Stream mapping:
  Stream #0:0 -> #0:0 (rawvideo (native) -> hevc (libx265))
Press [q] to stop, [?] for help
x265 [info]: HEVC encoder version 3.0_Au+25-39b35ea86283
x265 [info]: build info [Windows][GCC 9.1.1][64 bit] 10bit
x265 [info]: using cpu capabilities: MMX2 SSE2Fast LZCNT SSSE3 SSE4.2 AVX FMA3 BMI2 AVX2

Output #0, rawvideo, to 'pipe:':
  Metadata:
    encoder         : Lavf58.20.100
    Stream #0:0: Video: hevc (libx265), yuv420p10le, 1920x1080, q=2-31, 23.98 fps, 23.98 tbn, 23.98 tbc
    Metadata:
      encoder         : Lavc58.35.100 libx265

encoded 4316 frames in 52.01s (82.98 fps), 313.44 kb/s, Avg QP:34.64