.FLA File Format – Streams and their names

Contents

Every Flash document has one Contents stream. Its first byte is the document revision, which names the release that saved the file, and the rest is an archive of the document’s settings and lists: the scenes in order, the library, a record for each Media stream, the colours, the frame rate and the publish settings. It is the only way to know which scene or symbol each timeline stream is, and what the user called it. See The Contents stream.

Page streams

Up to Flash CS3, each scene’s timeline is a stream named Page, a space and a number: Page 1, Page 2 and so on, from 1. Flash CS4 names it P, the number and a time stamp, as below. The stream is an MFC archive holding one CPicPage object and everything under it: the layers, their keyframes and what is on the stage in each. See Pages, layers and frames.

The scenes are listed in order in Contents, one record for each.

Symbol streams

Each symbol in the library that has a timeline of its own, a movie clip, a button or a graphic, is a stream named Symbol and a number, Symbol 1 or Symbol 12, or in Flash CS4 S, a number and a time stamp. The stream has exactly the same form as a Page stream, a CPicPage tree. The symbol’s name is kept in Contents, with the rest of the library.

Media streams

Each imported bitmap or sound is a stream named Media and a number, Media 1 or Media 13, or in Flash CS4 M, a number and a time stamp. Unlike the others it is not an archive of objects. A JPEG is kept whole, starting FF D8; other bitmaps are kept in Flash’s own lossless form; sounds as PCM samples or MP3 frames. What the media is, and the file it was imported from, are in its record in Contents. See Bitmaps and sounds.

Flash CS4’s stream names

Flash CS4 names its timeline and media streams with a letter, the number and a time stamp, separated by spaces:

The time stamp is a Unix time in decimal: seconds since 1 January 1970. 1227523356 is 24 November 2008. Such names were seen in Flash CS4 documents (Contents revision 0x47) and in one Flash CS3 document (0x43). They are written in Contents like any other stream name, so a reader that follows Contents finds them. Whether Flash CS3 or earlier can open a document named this way is not known; Flash CS4 documents cannot be opened by CS3 in any case, and CS4 offers Save As CS3 for that.

Stream names and display names

The name a user sees, such as “Scene 1” or “Ball”, is not the stream’s name. For each scene, each symbol and each media item, Contents holds a record that gives first the stream’s name and then the display name. In this format the stream name is written as one length byte, the number of characters, followed by UTF-16LE, with no marker. The display name is an MFC string in its Unicode form, which starts FF FE FF.

17 06 50 00 61 00 67 00 65 00 20 00 31 00 FF FE FF 07 53 00 63 00 65 00 6E 00 65 00 20 00 31 00

This unmarked stream name is the change that makes this a separate format. A reader made for Flash MX and earlier reads the 06 as six single bytes, P.a.g., and loses its place; the marked strings, by contrast, say what they are. The directory of the compound file stores every stream name in UTF-16 in both formats, as the container requires.

To label a timeline, a reader takes each stream name from Contents, finds the stream of that name in the directory, and uses the display name that follows. The explorer labels every script this way, for example Scene 1 (Page 1).