I'm using Kdenlive v21.04.3 on Ubuntu 20.04.2. When I try to render, either the PC freezes, the PC reboots on its own, or Kdenlive stays up in various states. Occasionally Kdenlive provides an error log. Here is the output from the last failure:

x265 [info]: HEVC encoder version 3.2.1+1-b5c86a64bbbe x265 [info]: build info [Linux][GCC 9.3.0][64 bit] 8bit+10bit+12bit x265 [info]: using cpu capabilities: MMX2 SSE2Fast LZCNT SSSE3 SSE4.2 AVX FMA3 BMI2 AVX2 x265 [info]: Main profile, Level-4 (Main tier) x265 [info]: Thread pool created using 4 threads x265 [info]: Slices : 1 x265 [info]: frame threads / pool features : 2 / wpp(17 rows) x265 [info]: Coding QT: max CU size, min CU size : 64 / 8 x265 [info]: Residual QT: max TU size, max depth : 32 / 1 inter / 1 intra x265 [info]: ME / range / subpel / merge : hex / 57 / 2 / 2 x265 [info]: Keyframe min / max / scenecut / bias: 25 / 250 / 40 / 5.00 hx265 [info]: Lookahead / bframes / badapt : 15 / 4 / 0 x265 [info]: b-pyramid / weightp / weightb : 1 / 1 / 0 x265 [info]: References / ref-limit cu / depth : 2 / on / on x265 [info]: AQ: mode / str / qg-size / cu-tree : 2 / 1.0 / 32 / 1 x265 [info]: Rate Control / qCompress : CRF-23.0 / 0.60 x265 [info]: tools: rd=2 psy-rd=2.00 early-skip rskip signhide tmvp fast-intra x265 [info]: tools: strong-intra-smoothing lslices=6 deblock sao [mp4 @ 0x7f5b98000f40] Using AVStream.codec to pass codec parameters to muxers is deprecated, use AVStream.codecpar instead. [mp4 @ 0x7f5b98000f40] Using AVStream.codec to pass codec parameters to muxers is deprecated, use AVStream.codecpar instead.

I've tried lots of video output configurations, rendering to different folder locations, rendering short unedited clips. I was running with an onboard SSD hard drive (its built into the Gigabyte motherboard), and suspected it was a problem. So I just installed a new internal SSD HD, with a new copy of Ubuntu and Kdenlive, but it didn't help. On the old HD, I rolled back to Kdenlive v19 (with ubuntu 20.o4) but no joy. I use to render OK using an older version of Ubuntu and Kdenlive v19. I'm open to any suggestions. I'm at my wits end.

Here is another kdenlive report from another crash:

Rendering ... video/1st3clips2.mp4 crashed

no more csLADSPA plugins [mov,mp4,m4a,3gp,3g2,mj2 @ 0x7f33102219c0] Value 1.000000 for parameter 'seekable' out of range [-1 - 0] [mov,mp4,m4a,3gp,3g2,mj2 @ 0x7f3310240840] Value 1.000000 for parameter 'seekable' out of range [-1 - 0] [mov,mp4,m4a,3gp,3g2,mj2 @ 0x7f331047ed80] Value 1.000000 for parameter 'seekable' out of range [-1 - 0] [mov,mp4,m4a,3gp,3g2,mj2 @ 0x7f3310847440] Value 1.000000 for parameter 'seekable' out of range [-1 - 0] [mp4 @ 0x7f3310000f40] Using AVStream.codec to pass codec parameters to muxers is deprecated, use AVStream.codecpar instead. [mp4 @ 0x7f3310000f40] Using AVStream.codec to pass codec parameters to muxers is deprecated, use AVStream.codecpar instead.

On the latter crash, kdenlive kept running and Ubuntu generated its own crash report that included: "melt crashed with SIGSEGV". I haven't yet figured out how to copy the text from Ubuntu crash reports. Sorry about the changing fonts here. Its not something I did intentionally.

Here is another crash report. Rendering of /home/lekcin/Videos/Render 2.mp4 crashed

[mp4 @ 0x7f3804000f40] Using AVStream.codec to pass codec parameters to muxers is deprecated, use AVStream.codecpar instead. [mp4 @ 0x7f3804000f40] Using AVStream.codec to pass codec parameters to muxers is deprecated, use AVStream.codecpar instead.

Ubuntu also generated a crash report on this render crash. The Title is: melt crashed with SIGSEGV inx264_8_trellis_coefn()