x265enc only encodes one frame

[carial]

Hi:
I constructed the following gstreamer pipeline to encode YUV files with x265enc plugin:
gst-launch-1.0 filesrc location=./t.yuv ! videoparse format=2 width=3840 height=2160 framerate=24000/1001 ! x265enc bitrate=4000 speed-preset=2 ! h265parse ! filesink location=./t.h265
gstreamer version is 1.6.3. The pipeline does not report any error but it only encodes one frame (the first frame). Any possible reason?
By the way, I also tried the following pipeline but the same problem:
gst-launch-1.0 filesrc location=./t.yuv blocksize=12441600 num-buffers=120 ! video/x-raw,format=I420,width=3840,height=2160,framerate=24000/1001 ! x265enc bitrate=4000 speed-preset=2 ! h265parse ! filesink location=./t.h265 

Thank you for the kind help.
------- Yinqing
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