[FFmpeg-user] Why H264 Encoder is slower than H265 Encoder?

[Shi Qiu]

OS: Ubuntu 16.04 64bit
CPU: intel i7 6700

H264:
ffmpeg -hwaccel vaapi -hwaccel_output_format vaapi -hwaccel_device
/dev/dri/renderD128 -i a.h264 -c:v h264_vaapi -f h264 t.h264 -y

108fps

H265:
ffmpeg -hwaccel vaapi -hwaccel_output_format vaapi -hwaccel_device
/dev/dri/renderD128 -i a.h265 -c:v hevc_vaapi -f hevc t.h265 -y

126fps

Any ideas?