Maybe bottleneck for you is x265 so the speed difference between direct and piped is killed?
Here is x265 I built for the test above.
Edit:
tested with crf 18
pipe
Code:
avs2yuv_x64 -depth 10 1.avs -o - | x265.exe --y4m - --ctu 32 --preset ultrafast -o nul --pools 10 --crf 18 --frame-threads 2 > pipe.txt 2>&1
y4m [info]: 1920x1080 fps 24000/1001 i420p10 unknown frame count
raw [info]: output file: nul
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
encoded 4316 frames in 50.39s (85.64 fps), 1629.90 kb/s, Avg QP:24.65
direct
Code:
x265.exe 1.avs --ctu 32 --preset ultrafast -o nul --pools 10 --crf 18 --frame-threads 2 > direct.txt 2>&1
lavf [info]:
Format : avisynth
Codec : rawvideo ( raw video )
PixFmt : yuv420p10le
Framerate : 24000/1001
Timebase : 1001/24000
Duration : 0:03:00
lavf [info]: 1920x1080 fps 24000/1001 i420p10 frames 0 - 4315 of 4316
raw [info]: output file: nul
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
encoded 4316 frames in 55.19s (78.21 fps), 1629.90 kb/s, Avg QP:24.65
tested with crf 18 and asm sse4.2
pipe
Code:
avs2yuv_x64 -depth 10 1.avs -o - | x265.exe --y4m - --ctu 32 --preset ultrafast -o nul --pools 10 --crf 18 --frame-threads 2 > pipe.txt 2>&1 --asm sse4.2
y4m [info]: 1920x1080 fps 24000/1001 i420p10 unknown frame count
raw [info]: output file: nul
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 SSSE3 SSE4.2
encoded 4316 frames in 58.54s (73.73 fps), 1629.90 kb/s, Avg QP:24.65
direct
Code:
x265.exe 1.avs --ctu 32 --preset ultrafast -o nul --pools 10 --crf 18 --frame-threads 2 > direct.txt 2>&1 --asm sse4.2
lavf [info]:
Format : avisynth
Codec : rawvideo ( raw video )
PixFmt : yuv420p10le
Framerate : 24000/1001
Timebase : 1001/24000
Duration : 0:03:00
lavf [info]: 1920x1080 fps 24000/1001 i420p10 frames 0 - 4315 of 4316
raw [info]: output file: nul
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 SSSE3 SSE4.2
encoded 4316 frames in 61.19s (70.53 fps), 1629.90 kb/s, Avg QP:24.65
tested real encoding scenario where bottleneck is x265
pipe
Code:
avs2yuv_x64 -depth 10 1.avs -o - | x265.exe --y4m - --ctu 32 --preset slower --crf 18 -o nul --frame-threads 2 --no-amp --no-sao --no-strong-intra-smoothing > pipe.txt 2>&1 --asm avx512
y4m [info]: 1920x1080 fps 24000/1001 i420p10 unknown frame count
raw [info]: output file: nul
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 AVX512
encoded 501 frames in 153.32s (3.27 fps), 10340.94 kb/s, Avg QP:22.84
direct
Code:
x265.exe 1.avs --ctu 32 --preset slower --crf 18 -o nul --frame-threads 2 --no-amp --no-sao --no-strong-intra-smoothing > direct.txt 2>&1 --asm avx512
lavf [info]:
Format : avisynth
Codec : rawvideo ( raw video )
PixFmt : yuv420p10le
Framerate : 24000/1001
Timebase : 1001/24000
Duration : 0:00:20
lavf [info]: 1920x1080 fps 24000/1001 i420p10 frames 0 - 500 of 501
raw [info]: output file: nul
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 AVX512
encoded 501 frames in 153.33s (3.27 fps), 10340.94 kb/s, Avg QP:22.84