I have no plan to compete with our National Library located locally here :)
https://www-nrk-no.translate.goog/nordland/her-skal-den-norske-kulturarven-bevares-i-evig-tid-1.16277933?_x_tr_sl=no&_x_tr_tl=en&_x_tr_hl=en&_x_tr_pto=sc

but I prepare myself to test and use one method left with regards to "Personal Video Archiving".

Therefore I have ordered two selected, inexpensive devices (the urls here are just for English language):

1) Capture Card USB HDMI 4K to 1080P USB-C adapter (Speedy USB 3.2/3.1/3.0, 60 Hz and 1080p FHD.)
https://www.turascandinavia.com/en/products/computer/microphone-webcam/webcams/74257
2) Scart AV SV to HDMI Converter Switcher S Video Composite RCA DVD HD TV adapter (3-4 weeks delivery time
https://www.ebay.com.au/itm/295472602625

Q I have not yet found a definitiv ffmpeg FFV1 v 3 syntax guide for SD and HDV capturing and hope for suggestions and comments here!?

3.1 FFmpeg recipe (PAL)
ffmpeg -i VIDEO_IN \
-c:v ffv1 -level 3 -coder 1 -context 0 -slices 24 -slicecrc 1 \
-color_primaries bt470bg \
-color_trc bt709 \
-colorspace bt470bg \
-color_range mpeg \
-map 0 \
-top 1 \
-c:a copy \
-g 1 -pix_fmt + \
VIDEO_OUT.mkv

3.2 Reference Example
https://trac.ffmpeg.org/wiki/Encode/FFV1

    Copy audio "as-is" and use FFV1.3 as video codec.

    Parameters are 8 threads, coder=1, context=1, GOP-size=1, 24 slices and slice-CRC on:

    ffmpeg -i <input_video>     \
        -acodec   copy          \
        -vcodec   ffv1 -level 3 \
        -threads  8             \
        -coder    1             \
        -context  1             \
        -g        1             \
        -slices  24             \
        -slicecrc 1             \
        <output_video>


3.3 Various Encoding examples for Video capture from USB camera /dev/video0:

ffmpeg -f v4l2 -framerate 25 -video_size 720x576 -i /dev/video0 output_data.mkv

ffmpeg -f v4l2 -framerate 25 -video_size 720x576 -i /dev/video0 -codec:v ffv1 -codec:a pcm_s16le \
    -f matroska  output_video.mkv

Check that video is captured properly using ffplay:

ffmpeg -ar 44100 -thread_queue_size 1024 -f alsa -i $AUDIO \
    -r 25 -thread_queue_size 1024 -i $VIDEO \
    -codec copy -f matroska  - | ffplay -

Check the overall flow using ffplay before capturing:

ffmpeg -ar 44100 -thread_queue_size 1024 -f alsa -i $AUDIO \
    -itsoffset -0.5 -r 25 -thread_queue_size 1024 -i $VIDEO \
    -filter_complex 'channelmap=FL-0' -filter_complex 'crop=w=700:h=556:x=8:y=0' \
    -map 1:v  -map 0:a -codec:v ffv1 -codec:a pcm_s16le \
    -f matroska  - | ffplay -



4, Regarding FFV1 lossless compression in realtime
Comparison tests (2013/2015) have shown that FFV1 produced the smallest files at the fastest speed. It can be used to capture SD material in realtime, and HD possibly, too. This according to a 2012/2015 article, where I have extracted the results for FFV1 v.3 in the tables below:

http://www.av-rd.com/knowhow/video/comparison_video_codecs_containers.html#codec_tests

NOTE: This is a consumer grade, off-the-shelf PC setup.

Hardware:
CPU: Intel(R) QuadCore(TM) i7-2600K CPU @ 3.40GHz
RAM: 8 GB
Disk: Intel SSDSA2CW080G3 (SSD)
Software:
Operating System: GNU/Linux (Xubuntu 12.04.1, 64bit)
Transcoding tool: FFmpeg (version git N-59183-g3e62654, Dec 17 2013)


Video source file: VQEG reference video "football" (NTSC-SD, 720x486px, 30fps, yuv422p, 8bpc)
Codec Encoding Decoding Filesize % of uncompressed Implementation Details
FFV1 (version 3) 216 fps 277 fps 111 MiB 46.1% libavcodec (FFmpeg) log, framemd5


Video source file: SVT reference video "park joy" (full-HD/1080p, 1920x1080px, 50fps, yuv420p, 8bpc)
Codec Encoding Decoding Filesize % of uncompressed Implementation Details
FFV1 (version 3) 31 fps 63 fps 879 MiB 57.2% libavcodec (FFmpeg) log, framemd5



PAL-SD 720x576 stored as YUV422, 10 bpc (bits per component), instead of the tested 8 bpc above, seems to me would have enlarged the the filesizes with about 25%, or to about 40 GB/hr with FFV1 lossless compressed.

Although the FFV1 compression results above obviously used yuv422p, 8bps source SD and FHD files as input, it seems for me that the encoding speeds at 216 fps and 31 fps for SD and FHD respectively, assumingly should manage realtime FFV1 encoding and streaming of PAL SD and HDV at 25 fps as well, especially with a faster i7-6700 x 8 cpu. Comments here?


5. Related 2021-[Cin] threads as background references

[Cin] hdmi capture card (with v4l2)
https://www.mail-archive.com/cin@lists.cinelerra-gg.org/msg02865.html

[Cin] offtopic: Digitize and record Video with A/D USB adapters
https://www.mail-archive.com/cin@lists.cinelerra-gg.org/msg03269.html

[Cin] offtopic: HDMI capture
https://www.mail-archive.com/cin@lists.cinelerra-gg.org/msg02084.html

[Cin] Is SD and HD 422 Video Capture obtainable with V4L(2)?
https://www.mail-archive.com/cin@lists.cinelerra-gg.org/msg03719.html

[Cin] Uncompressed video to lossless compression FFV1/MKV
https://www.mail-archive.com/cin@lists.cinelerra-gg.org/msg03791.html