Converting .thumbdata to .mp4 format.
Converting Android Gallery Thumbnail Index files directly to MPEG-4 Videos (.thumbdata to .mp4 conversion) is not possible. THUMBDATA 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 thumbdata to mp4 conversion is not possible.
So don't expect any so-called thumbdata to mp4 converter or thumbdata to mp4 free online conversion tool available.
The database currently does not contain any thumbdata software converter.