[FFmpeg-user] 3D block_lr or frame-packing to side-by-side format

[ffmpeg at windfinder.com.br]

Hi there,

I'm trying to convert a 3D mkv file from "stereo_mode: block_lr" or 
"frame-packing 3d" to a mkv file that uses side-by-side (or top-bottom) 
stereo3d instead - to be viewed using an Epson projector with active 3D 
glasses (a setup that works well with side-by-side or top-bottom 3D files).

The input file has these characteristics:
Stream #0:0(eng): Video: h264 (High), yuv420p(tv, bt709, progressive), 
1920x1080 [SAR 1:1 DAR 16:9], 23.98 fps, 23.98 tbr, 1k tbn, 47.95 tbc
     Metadata:
       stereo_mode     : block_lr

       3d-plane-eng    : 0

I've tried several different options, such as:
ffmpeg -i input_file.mkv -vf "stereo3d=al:sbsl,scale=1920x1080" -aspect 
16:9 output_file.mkv
ffmpeg -i input_file.mkv -vf "stereo3d=al:sbsl" -c:a copy output_file.mkv
... -vf "stereo3d=icl:sbsl" -c:a copy ...
... -vf "stereo3d=al:ab2l" -c:a copy ...
... -vf "stereo3d=al:abl" -c:a copy ...

Some of those options created files that show some 3D depths and seem 
"OK" when the scenes are mostly static or have slow movements, but for 
fast-moving scenes the results were not good and looked very "broken".

During the conversion, I see several error or warning messages repeated 
multiple times:
[h264 @ 0x55a12faf1c40] SEI type 0 overread by 7 bits
[h264 @ 0x55a12faf1c40] SEI type 6 size 536 truncated at 40
[h264 @ 0x55a12fa4bc80] sps_id 1 out of range
[h264 @ 0x55a12fa4bc80] SEI type 37 size 1032 truncated at 1024

I've tried the ffmpeg available in Ubuntu 20.04 LTS (via apt), and I've 
also tried purging the apt package and compiling ffmpeg from the 
source-code (snapshot) - same results (and same error & warning messages).

Does anyone know how to convert 3D files from Blu-ray discs 
(alternate-frame or block_lr or frame-packing 3d) into side-by-side or 
top-bottom files?

Thanks,
JC