[FFmpeg-devel] Speed difference when using ffmpeg + x264 with stdin, or libx264

[Pradeep Ramachandran]

Hi,
I am trying to encode an 8-bit 4K video at 3Mbps by using ffmpeg + x264 and
I see a considerable difference in speed when I use ffmpeg and pipe the
output to x264 (by using linux pipes), and when I use libx264. The speed
difference is nearly 2X with the encoding being considerably faster when
using libx264. When I use just x264, I see that the speed is comparable to
using libx264 in ffmpeg.

My command lines are below

Using ffmpeg + x264: ffmpeg -s 3840x2160 -r 50 -i
Samsung_UHD_Soccer_Barcelona_Atletico_Madrid_8bit.yuv -f rawvideo - |
./x264 --input-res 3840x2160 --fps 50 --keyint 100 --preset ultrafast -o
/dev/null --bitrate 5000 --vbv-maxrate 5000 --vbv-bufsize 6000 - (runs at
approx 70fps)

Using ffmpeg + libx264: ffmpeg -s 3840x2160 -r 50 -i
/home/mcw/Videos/Samsung_UHD_Soccer_Barcelona_Atletico_Madrid_8bit.yuv -c:v
libx264 -preset ultrafast -b:v 5000k -f mp4 Barca_libx264.mp4 (runs at
approx 128fps)

Has anyone else experienced such a stark difference in speed? Are the
limits of linux pipes the reason for this difference, or is there something
else going on here?

Pradeep.