[FFmpeg-user] Blender animation: , replaceing part of an animation with another one

[tuxic at posteo.de]

Hi,

rendering an animation with Blender is a time consuming task - at
least with "normal" hardware.
And refining the animation means doing the above quite often until
everything fits.

To save time I would like to do the following:
Render the complete animation once.
Check the result
Pinpoint parts with problems
Correct those problems
Rerender only the according part of the animation
Last step:
And finally replace the corresponding part of the complete animation with 
the corrected pary (both given by start and end frame).

How can I do the "last step" with ffmpeg while preserving as much of
the quality as possible in a compact command.

I do not fear the commandline and I am using ffmpeg on Linux.

At this stage the animation has no audio.
ffprobe says about the animation video:


  Metadata:
    SCENE           : Scene
    FILE            : <file>
    DATE            : 2020/10/03 07:07:45
    ENCODER         : Lavf58.29.100
  Duration: 00:00:54.54, start: 0.000000, bitrate: 3671 kb/s
    Stream #0:0: Video: h264 (High), yuv420p(progressive), 976x1440 [SAR 1:1 DAR 61:90], 24 fps, 24 tbr, 1k tbn, 48 tbc (default)

The file format is mkv.

Thanks a lot for any help in advance.

Cheers!
Meino