Niconico Douga to MP3

Yes, and those are the main use for this page: a single track behind a static or looped picture. The MP3 is the upload's own audio encoded once, so a cover sounds the way it does on the site rather than like a second recording made through a speaker.

Because the audio arrived with the video. Niconico publishes the track inside the video container, so the ceiling is whatever that upload carried. Re-encoding at a higher bitrate would double the file size and change nothing audible — a common trick that is skipped here.

The platform refuses the request before a stream exists to extract from. That is not a limitation of the extractor: the same link fails on the video download route too. A public video available in your region parses normally, and no account is ever asked for.

No. Public videos are readable without one, which is the point of pasting a link into a browser tool. Videos the platform marks as login-required stay out of reach, and no credentials are requested in an attempt to get around that check.

Seconds for a typical upload. The fetcher pulls the audio stream, ffmpeg encodes it once, and the download begins. The only wait is the concurrency limit: two jobs at a time per address, one per IP, so a third request queues briefly instead of failing.

Yes — use the Niconico video downloader page with the same link, where the 360p and 240p tiers are listed. The two routes are independent, so taking both means two parses, and the concurrency limit counts them as two separate jobs.

Yes. Duration comes from the audio track inside the source container, with no trimming of the intro and no fade at the end. A three-minute upload produces a three-minute file, and a looped or static picture behind the track changes nothing about that.

No daily count and no account. The caps are two concurrent jobs, one per IP, and two hours on a single video. Everything else is unlimited: a hundred tracks in a row is fine, two at a time, for as long as you keep pasting watch links into the box.