Convert THUMBDATA3--1967290299 to MP4

Converting Android Gallery Thumbnail Index files directly to MPEG-4 Videos (.thumbdata3--1967290299 to .mp4 conversion) is not possible. THUMBDATA3--1967290299 files found on SD cards of Android devices contain cached thumbnail data of images. They neither contain documents, nor any other multimedia data, which is why it is not possible to extract, export or convert these files to any other format, including MP4.

In a word, direct thumbdata3--1967290299 to mp4 conversion is not possible.
So don't expect any so-called thumbdata3--1967290299 to mp4 converter or thumbdata3--1967290299 to mp4 free online conversion tool available.