struct swf_definebitslossless {
	swf_long_tag		f_tag;		/* 20 or 36 */
	unsigned short		f_image_id;
	unsigned char		f_format;	/* 3, 4 or 5 */
	unsigned short		f_width;
	unsigned short		f_height;
	if(f_format == 3) {
		unsigned char	f_colormap_count;
		if(f_tag == DefineBitsLossless) {
			swf_rgb		f_colormap[f_colormap_count];
		}
		else {
			swf_rgba	f_colormap[f_colormap_count];
		}
		unsigned char	f_indices[((f_width + 3) & -4) * f_height];
	}
	else {
		if(f_tag == DefineBitsLossless) {
			swf_xrgb	f_bitmap[f_width * f_height];
		}
		else {
			swf_argb	f_bitmap[f_width * f_height];
		}
	}
};

These tags declares a loss-less image bitmap. It has a small header followed by an optional colormap and the bitmap data. When we have a colormap, the bitmap data is an array of indices in the colormap aligned to 4 bytes on a per row basis.

There are three supported formats:

...

Format No. (bits)	Color Format		Comments
	Without Alpha	With Alpha
3 (8 bits(1))	RGB

The original document by Steve Hollasch can be found at http://steve.hollasch.net/cgindex/coding/ieeefloat.html

IEEE Standard 754 Floating Point Numbers

Steve Hollasch / Last update 2005-Feb-24

IEEE Standard 754 floating point is the most common representation today for real numbers on computers, including Intel-based PC's, Macintoshes, and most Unix platforms. This article gives a brief overview of IEEE floating point and its representation. Discussion of arithmetic implementation may be found in the book mentioned at the bottom of this article.

What Are Floating ...

struct swf_soundstreamblock {
	swf_long_tag		f_tag;		/* 19 */
	unsigned char		f_sound_data[variable size];
};

The SoundStreamBlock tag defines the data of a sound effect previously defined with a SoundStreamHead or a SoundStreamHead2 tag.

WARNING: This tag requires you to save the swf_tag structure in long format whatever the size of the data (i.e. f_tag_and_size & 0x3F == 0x3F always true even if the size is 62 or less.)

The data depends on the SoundStreamHead[2] definition and is variable in size. Please, see the DefineSound tag for more information about sound data.

struct swf_definesound {
	swf_tag			f_tag;		/* 14 */
	unsigned short		f_sound_id;
	unsigned		f_sound_format : 4;
	unsigned		f_sound_rate : 2;
	unsigned		f_sound_is_16bits : 1;
	unsigned		f_sound_is_stereo : 1;
	unsigned long		f_sound_samples_count;
	unsigned char		f_sound_data[<variable size>];
};

A DefineSound tag declares a set of samples of a sound effect or a music.

The sound samples can be compressed or not, stereo or not and 8 or 16 bits. The different modes are not all available in version 2, although the same tag is used in newer versions with additional capabilities.

The f_sound_is_16bits is always set to 1 (16bits samples) if the samples are compressed (neither Rawnor Uncompressed).

The f_sound_rate represents the rate at which the samples are defined. The rate at which it will be played on the target computers may differ. The following equation can be used to determine the ...

struct swf_doaction {
	swf_tag			f_tag;		/* 12 and 59 */
	if(f_tag == DoInitAction) {
		unsigned short	f_action_sprite;
	}
	swf_action		f_action_record[variable];
};

The DoAction tag will be used to execute a set of actions in place. Usually, actions are used on buttons to add interactivity to the SWF movies. In version 1 you had only one dynamic branch (WaitForFrame). In version 4 you can test many different things such as a position, angle or sound track cursor position. Since version 5, SWF has a complete scripting language supporting string and arithmetic operations.

struct swf_definebutton {
	swf_tag			f_tag;		/* 7 */
	unsigned short		f_button_id;
	swf_button		f_buttons;
	swf_action		f_actions;
};

Mouse interactivity in the SWF format comes from the buttons. All the buttons have an identifier and can be placed in the display list like any other shape.

A buttons has different states. Some states can be entered only when the button was in a specific state before (like a button being pushed).

Buttons can be represented graphically in any manner you want. Each state can use a different edit text, shape, sprite or text to render the button.

struct swf_definebitsjpeg {
	swf_long_tag		f_tag;		/* 6, 21, 35 or 90 */
	unsigned short		f_image_id;
	if(f_tag == DefineBitsJPEG3 + f_tag == DefineBitsJPEG4) {
		/* sizeof(f_encoding_tables) + sizeof(f_image_data) + 2 when JPEG4 */
		unsigned long		f_offset_to_alpha;
	}
	if(f_tag == DefineBitsJPEG4) {
		unsigned short fixed	f_deblocking_filter_parameter;
	}
	if(f_tag != DefineBitsJPEG) {
		/* when DefineBitsJPEG, use JPEGTables instead */
		unsigned char		f_encoding_tables[<variable size>];
	}
	unsigned char		f_image_data[<variable size>];
	if(f_tag == DefineBitsJPEG3 || f_tag == DefineBitsJPEG4) {
		unsigned char		f_alpha[<variable size>];
	}
};

These tags define an image saved using the JPEG compression scheme.

DefineBitsJPEG (V1.0) does not include the encoding tables which are defined in the unique JPEGTables tag instead. All the DefineBitsJPEG of an SWF file use the only JPEGTables tag. Yes... This means you need a tool that is capable of reusing the same tables over and over again to make sure that all your DefineBitsJPEGs work properly (or use it just once.)

The other tags incorporate their own version of the JPEG encoding tables.

The DefineBitsJPEG3 and DefineBitsJPEG4 support an alpha channel bit plane (8 bits.) ...

struct swf_tag {
	unsigned short		f_tag_and_size;
	f_tag = f_tag_and_size >> 6;
	f_tag_data_size = f_tag_and_size & 0x3F;
	if(f_tag_data_size == 63) {
		unsigned long	f_tag_data_real_size;
	}
	else {
		f_tag_data_real_size = f_tag_data_size;
	}
};

struct swf_long_tag { /* i.e. the last 6 bits of f_tag_and_size = 0x3F */
	unsigned short		f_tag_and_size;
	f_tag = f_tag_and_size >> 6;
	unsigned long	f_tag_data_real_size;
};

The tag and size are saved in a 16 bits little endian unsigned integer. The tag is always aligned to a byte (not a bit). The size is defined in the lower 6 bits. And the short value is in a little endian format as expected by the declaration. If the size is 63 (0x3F), then another 4 bytes are read for the size. This is used for really large tags such as fonts with many characters, audio, video, or images.

Brief History

At the very beginning, a company created the SWF format to generate small vector animations on the Internet called Shockwave Flash (hence the name of the format, SWF.) It also included images. This company was bought by Macromedia around 1997 (if I recall properly). This is when Flash v3 was created. Since then, Macromedia created a new version about once a year up to version 8. At that time (in 2005/2006), Macromedia sealed a deal with Adobe which wanted to use the SWF format in their PDF files.

Today (May 1st, 2008), the SWF format is available for free to all.

There was ...

SSWF™ name

The name SSWF™ is used by Made to Order Software to reference its SWF library. You are welcome to use this name in reference the SSWF library if you use it in your own software.

SWF Format

Please, note that there is no restriction in using this document. However, the SWF format copyright holders are Macromedia and Adobe. There may be limits in what you can do using this format. If you are not sure, I suggest you contact a knowledgeable copyright and Software attorney who can help you decide what you can do with the SWF format.