On Wednesday, July 21, 2021, Andrea paz <gamberucci.andrea@gmail.com> wrote:
I downloaded a new ffmpeg-4.4.tar.xz and now the compile error
happened a little bit later. I attach the cin5.log.
However I think that the fault is not the tar.xz but mine, that I had
removed also the ffmpeg.git patches, during some tests, in addition to
the ffmpeg-4.3 patches

ffmoeg. git patches only should be relevant / active if you add - - with-git-ffmpeg=url to your configure.... 
 

PS: I tried a build without patches, but including the 3 of h265
present in git. The installation works, but trying to render using
h265 at 10bit and h265 at 12bit, leads to these errors:

[libx265 @ 0x7f3fa57f2400] Specified pixel format yuv422p10le is
invalid or not supported
FFMPEG::open_encoder  err: Invalid argument
int FFMPEG::open_encoder(const char*, const char*):
open failed libx265:/home/paz/video_editing/prova/10bit.mp4
Render::render_single: Session finished.
[libx265 @ 0x7f3fa57ef400] Specified pixel format yuv422p12le is
invalid or not supported
FFMPEG::open_encoder  err: Invalid argument
int FFMPEG::open_encoder(const char*, const char*):
open failed libx265:/home/paz/video_editing/prova/12bit.mp4
Render::render_single: Session finished.


can you check if resulting x265.a library (in thirdparty/x265-3.4) contains 10 and 12 bit symbols? 

just to be clear, you applied x265-multilib patch and it applied correctly (check with git apply -v, just git apply may not return error just silently skip patching)