Holding a mouthpiece close while speaking, she said: "If something happens to me , these people will be responsible. I want to marry Imran."
It is not clear who put up the video but it went viral on Tuesday. By then, Soni, 26, was dead.
The police, after watching the clip online, came to her village in Hathras in western Uttar Pradesh. Based on the video, they have filed an FIR or complaint charging six members of her family - her parents and four brothers. All are missing.
The family lived in Mumbai but allegedly took Soni to their village in UP.
Her body was exhumed on Tuesday but no tell-tale marks were found and a post mortem has not established how she died. Her samples have been sent for a forensic test.
Villagers say Soni arrived with her family a few days ago. Last Friday, they said, the family told them she had died, no reasons given.
It's not clear when this video was filmed.
A police team has been sent to Mumbai and the police are also trying to contact Imran, the man she referred to in the video.
"With the help of the video clip we got all the information. Treating it as an FIR, we have registered a complaint against six of them," said Ram Moorat Yadav, a senior police officer in Hathras.
The police say they don't have any details yet of when and where the video was filmed, except that it looks like a train toilet. Police sources also say it is possible that someone filmed the video for her, but it is not clear who.