In kdenlive is setup like this:
Rendern H264 2000kbps 2pass
f=mp4 hq=1 acodec=aac ab=128k ar=48000 pix_fmt=yuv420p vcodec=libx264 minrate=0 b=2000k b_strategy=1 subcmp=2 cmp=2 coder=1 flags=+loop flags2=dct8x8 qmax=51 subq=7 qmin=10 qcomp=0.6 qdiff=4 trellis=1 aspect=%dar pass=2


in video is this info:
Encoding settings : cabac=1 / ref=1 / deblock=1:0:0 / analyse=0x3:0 / me=dia / subme=7 / psy=1 / psy_rd=1.00:0.00 / mixed_ref=0 / me_range=4 / chroma_me=0 / trellis=1 / 8x8dct=1 / cqm=0 / deadzone=21,11 / fast_pskip=0 / chroma_qp_offset=-2 / threads=1 / sliced_threads=0 / nr=0 / decimate=1 / mbaff=0 / constrained_intra=0 / bframes=0 / wpredp=0 / keyint=12 / keyint_min=7 / scenecut=0 / intra_refresh=0 / rc=2pass / mbtree=0 / bitrate=2000 / ratetol=2.0 / qcomp=0.60 / qpmin=10 / qpmax=51 / qpstep=4 / cplxblur=20.0 / qblur=0.5 / ip_ratio=1.25 / aq=1:1.00




I want this: screenshot: setup x264.jpg
in video is this info with the settings i want:
Encoding settings : cabac=1 / ref=5 / deblock=1:0:0 / analyse=0x3:0x133 / me=umh / subme=9 / psy=1 / psy_rd=1,00:0,00 / mixed_ref=1 / me_range=16 / chroma_me=1 / trellis=0 / 8x8dct=1 / cqm=0 / deadzone=21,11 / fast_pskip=1 / chroma_qp_offset=-2 / threads=3 / sliced_threads=0 / nr=0 / decimate=1 / mbaff=0 / constrained_intra=0 / bframes=5 / b_pyramid=2 / b_adapt=1 / b_bias=0 / direct=1 / wpredb=1 / wpredp=2 / keyint=500 / keyint_min=50 / scenecut=40 / intra_refresh=0 / rc_lookahead=40 / rc=crf / mbtree=1 / crf=22,0 / qcomp=0,60 / qpmin=10 / qpmax=51 / qpstep=4 / ip_ratio=1,40 / aq=1:1,00


how to setup the x264 encoder, what to write
please help.

I'm not quite sure what you want exactly?
Do you want to create a custom render profile?
You can add one, by clicking on the icon with the small green plus in the row with the big drop-down to switch between PAL and NTSC (directly above the profile list).

i did try this:
f=mp4 hq=1 acodec=aac ab=160k ar=48000 pix_fmt=yuv420p vcodec=libx264 crf=22 bframes=5 b-pyramid=1 weightb=1 ubme=9 ref=5 threads=3 mixed-refs=1 keyint=500 min-keyint=50 scenecut=40


results in:
Rendern von /home/woda/kdenlive/Unbenannt test 4.mp4 abgestürzt
x264 [info]:
using cpu capabilities: MMX2 SSE2Fast SSSE3 FastShuffle SSE4.1 Cache64




and how to 5.1 aac?

When does the crash appear:
Beginning?
99%?
Somewhere else?

@ttill: it is at the begin.


i do try now do small steps and mod the render-profile.

in this test profile with 3 reference frames it produced video with 1 ref-frame.
f=mp4 hq=1 acodec=aac ab=128k ar=48000 pix_fmt=yuv420p vcodec=libx264 crf=22 ref=3 b_strategy=1 subcmp=2 cmp=2 coder=1 flags=+loop flags2=dct8x8 qmax=51 subq=7 qmin=10 qcomp=0.6 qdiff=4 trellis=1 aspect=%dar

info in video:
Encoding settings : cabac=1 / ref=1 / deblock=1:0:0 / analyse=0x3:0 / me=dia / subme=7 / psy=1 / psy_rd=1.00:0.00 / mixed_ref=0 / me_range=4 / chroma_me=0 / trellis=1 / 8x8dct=1 / cqm=0 / deadzone=21,11 / fast_pskip=0 / chroma_qp_offset=-2 / threads=1 / sliced_threads=0 / nr=0 / decimate=1 / mbaff=0 / constrained_intra=0 / bframes=0 / wpredp=0 / keyint=12 / keyint_min=7 / scenecut=0 / intra_refresh=0 / rc=crf / mbtree=0 / crf=22.0 / qcomp=0.60 / qpmin=10 / qpmax=51 / qpstep=4 / ip_ratio=1.25 / aq=1:1.00



and in this test profile with 3 reference frames and me=umh it produced video with 1 ref-frame and me=dia.
f=mp4 hq=1 acodec=aac ab=128k ar=48000 pix_fmt=yuv420p vcodec=libx264 crf=22 ref=3 me=umh b_strategy=1 subcmp=2 cmp=2 coder=1 flags=+loop flags2=dct8x8 qmax=51 subq=7 qmin=10 qcomp=0.6 qdiff=4 trellis=1 aspect=%dar

info in video:
Encoding settings : cabac=1 / ref=1 / deblock=1:0:0 / analyse=0x3:0 / me=dia / subme=7 / psy=1 / psy_rd=1.00:0.00 / mixed_ref=0 / me_range=4 / chroma_me=0 / trellis=1 / 8x8dct=1 / cqm=0 / deadzone=21,11 / fast_pskip=0 / chroma_qp_offset=-2 / threads=1 / sliced_threads=0 / nr=0 / decimate=1 / mbaff=0 / constrained_intra=0 / bframes=0 / wpredp=0 / keyint=12 / keyint_min=7 / scenecut=0 / intra_refresh=0 / rc=crf / mbtree=0 / crf=22.0 / qcomp=0.60 / qpmin=10 / qpmax=51 / qpstep=4 / ip_ratio=1.25 / aq=1:1.00

what for is this profile??????????????????????????????????????????????????????????

Sorry, but I have no idea how to handle your problem.
Maybe someone else can help.