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A centralized website that will let you download videos from Twitter as MP4 files. This is not a decentralized service by any means, but it is a great tool to capture videos that might be censored by Twitter, where you can the re-upload them to a decentralized service.
SaveTweetVid might not work without centralized DNS.
It might not work without central servers.
It's unknown or not applicable as to how user accounts are handled. It's unknown or is not applicable if SaveTweetVid supports cryptocurrency monetization.