Kling 1.5 video production based on Alheim's "Red's #NoFilter Moment", https://www.deviantart.com/aiheim/art/Red-s-NoFilter-Moment-1068233106

Cloned from parent post 62863 with AI voice-over lip-synched using that new feature in Kling (Oct 2024), as a "sample" for demonstration purposes rather than polished work.

Voice-over created and recorded offline from https://elevenlabs.io/ .

Notes:

Kling's lip-synch successfully identified one human(oid) character to lip-synch... I've not yet tried this with two!

It will not lip-synch with a feral for those I've tried - which is probably just as well - but that is also indicative that Kling doesn't attempt to use the existing video so much as "over-stamp" new video for the lips.
This is most apparent at the end of this vid where Red's expression doesn't return to a smile per the original generated video but instead to a neutral expression (resting bitch face? *jkjkjk*). I deliberately trimmed this just at that point to show the transition, but the expression continues neutral and somewhat awkward beyond that point.
So... have a voice sample which runs right to the end of the video and/or leading to a state where closed lips appears natural for that point in the animation?

A minor "head tilt" is semi-successfully coped-with in this lip-synch test: a little awkwardness at the start followed by a change in the size of lips, which is probably not helped by the AI trying to include the brightness of the sun in the processing.

02c only, anyhow. Have fun if trying this out! (Personally I prefer the silent, smiling version, but good to experiment. Background nature sounds next? :)