On Sony HX-series cameras, file numbering is typically based on the files already present in the recording folder. If the folder changes, numbering may restart at 0001; if the folder already contains files, the camera usually assigns the next number after the highest existing file.

What to try:

• Use a freshly formatted card.
• Create or select a new recording folder if your camera allows it.
• Put files on the card in the relevant AVCHD folder using the same naming pattern as the camera’s video files.
• The camera may then continue from the highest existing number.

A simple test is to add a few dummy files with the expected extension and sequential numbers, then record a clip and see whether the camera uses the next number.

Important: because AVCHD uses a specific folder structure, back up your card first and test carefully. If the camera changes to a new folder, numbering may restart again. There may not be a direct menu option to manually set the starting number; the practical workaround is to let the camera detect existing numbered files in the target folder.