What is wrong with FB recording ?

[r3d 9u11]

Hello. I'm trying to record framebuffer fb0, but something went wrong.
The problem on armhf i.mx6-based SoM (on the PC looks like OK).

For test I used command:
while [ true ] ; echo `date` > /dev/tty0 ; sleep 1s ; done &

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with ffmpeg all is OK: https://youtu.be/1iiEpE35aDY

cmd:
ffmpeg -f fbdev -i /dev/fb0 output.avi

output: https://pastebin.com/0e6MkiiF

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but with gstreamer-1.0 I can't record it normally, I can't understand why:

25FPS: https://youtu.be/Ba8vaqyNc40 (too fast)

cmd:
gst-launch-1.0 -v multifilesrc location=/dev/fb0 \
! videoparse format=bgra width=1280 height=720 framerate=25 \
! avimux ! filesink location=gst25.avi

output: https://pastebin.com/wPDdhaQe

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4.3FPS: https://youtu.be/cLXtM9YAurE (too slow and some frames were missed)

cmd:
gst-launch-1.0 -v multifilesrc location=/dev/fb0 \
! videoparse format=bgra width=1280 height=720 framerate=17/4 \
! avimux ! filesink location=gst4.3.avi

output: https://pastebin.com/ma91jgGT

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What I'm doing wrong?
Help, please.
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