but somehow extracted with a slightly longer interval (included about 7 seconds before the specified time interval)

That is normal. ffmpeg can only cut the video at nearest keyframe

and that also seems to be slower than typical download so I was wondering if there is another option.

It is slower because we are using ffmpeg to do the download. There is no other option

That is normal. ffmpeg can only cut the video at nearest keyframe

This isn't true, I regularly use FFmpeg to cut video accurately, it's perfectly possible to do when encoding the video (i.e. when not specifying c- copy or -c:v copy), it would make FFmpeg a very useless video editor otherwise. The problem is that it's done by using -ss and -t/-to to seek through the input rather than the output, but it appears yt-dlp defaults to always seeking through the output when using --external-downloader-args. See here for more information on seeking on input vs output.

but yt-dlp doesn't appear to allow this with the --external-downloader-args options

Just remove the _i to change it to an output arg

--external-downloader-args "ffmpeg:-ss ... -to ..."

but yt-dlp doesn't appear to allow this with the --external-downloader-args options

Just remove the _i to change it to an output arg

--external-downloader-args "ffmpeg:-ss ... -to ..."

Yeah my bad, you're right, I was confusing the seeking options even though I linked to the FFmpeg wiki page that explains them - seeking on input is the least accurate because it uses keyframes, not seeking on output. Seeking on output is what was necessary for accurate seeking.

The problem is that when I seek on output with:

yt-dlp --downloader ffmpeg --external-downloader-args "-ss 00:40:00.00 -to 00:40:55.00" "https://www.youtube.com/watch?v=w53JbQ4pMjE"

...I get the following error:

[tls @ 0000023ad84fa700] Error in the pull function.0:00.00 bitrate=N/A speed=   0x
[matroska,webm @ 0000023ad8501540] Read error
[tls @ 0000023ad84fa700] The specified session has been invalidated for some reason.
    Last message repeated 1 times
https://rr2---sn-8vq54vox03-xqpe.googlevideo.com/videoplayback?expire=1641423505&ei=Mc7VYebpArjCmLAP_b-44
As&ip=90.246.120.252&id=o-AN7HZ7YU5mN6DPHorgYqqM63DZfz9iwDtlCK9unur2jy&itag=251&source=youtube&requiressl
=yes&mh=Xi&mm=31%2C29&mn=sn-8vq54vox03-xqpe%2Csn-aigl6ner&ms=au%2Crdu&mv=m&mvi=2&pl=18&initcwndbps=196500
0&vprv=1&mime=audio%2Fwebm&gir=yes&clen=51983825&dur=3525.081&lmt=1633347724405414&mt=1641401582&fvip=2&k
eepalive=yes&fexp=24001373%2C24007246&c=ANDROID&txp=5432434&sparams=expire%2Cei%2Cip%2Cid%2Citag%2Csource
%2Crequiressl%2Cvprv%2Cmime%2Cgir%2Cclen%2Cdur%2Clmt&sig=AOq0QJ8wRQIgQr7qjDNTd5Rvp27JbLDkPkRLyRDHjBypryo1
vyxM5oICIQC6U2WVmgC-nIHo8YdsN3pX6CEmLxQf4wStAn5avn6nUA%3D%3D&lsparams=mh%2Cmm%2Cmn%2Cms%2Cmv%2Cmvi%2Cpl%2
Cinitcwndbps&lsig=AG3C_xAwRQIhAM1xfnu4ugRPg15TuqU-Q6Jh8sHgOCUfeYycCF1C6iHWAiAE9uDjprUxGEWMosAaKsdwmQjA3A3
7ZLnYyhekXKr9iw%3D%3D: I/O error
frame= 1569 fps=1.9 q=-1.0 Lsize=    3539kB time=00:00:54.96 bitrate= 527.5kbits/s speed=0.0674x
video:3528kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.332972%
[ffmpeg] Downloaded 3624339 bytes
[download] 100% of 3.46MiB in 13:36

And an output clip that is time-accurate but with no audio. Any idea how this might be fixed?

I can reproduce, but no idea why

No longer reproducible