This repository defines an unofficial standard for a file format standard. Its main use is to create file that except their payload contain small pieces of text (captions) about that fil
The CPTN file is a semi-binary file. That means that if you open it in a text editor, you would be seeing nonsense characters for the most part (except the magic number and the text caption). That is because a CPTN file contains both binary data (header and possibly the payload content) and text data (the payload except maybe the content)
The file consists of two parts: the header and the payload. The header is full of binary data, while the payload is full of text data (except the content, which can contain both/either binary and/or text data).
The header data are in the following format:
| Offset | Size | Name | Description |
|---|---|---|---|
| 0 | 5 | Magic number | Magic number 0x4350544E0A (CPTN/n) |
| 5 | 1 | Filename size | Filename size in bytes or characters (it can also contain nothing, AKA 0x00 AKA a null byte) |
| 6 | 2 | Caption size | Length of the caption text in bytes (max is 2^16 or about 65k, probably enough for a caption) |
The payload data are in the following format:
| Size | Name | Description |
|---|---|---|
| Defined in file header as Filename size | Filename | Contains the filename of the original file (if any) |
| Defined in file header a Caption size | Caption | Contains the text caption of the file |
| Remaining bytes of the file | Content | Contains the main content of the file |
This file format is intended to be used to add captions to already existing files, although it can also be used to generate new files