SWF

struct swf_soundstreamhead {
	swf_tag			f_tag;		/* 18 or 45 */
	unsigned		f_compression : 4;
	unsigned		f_sound_rate : 2;
	unsigned		f_sound_size : 1;
	unsigned		f_sound_stereo : 1;
	unsigned		f_reserved : 4;
	unsigned		f_playback_rate : 2;
	unsigned		f_playback_size : 1;
	unsigned		f_playback_stereo : 1;
	unsigned short		f_sample_size;
	if(f_compression == 2) {
		signed short	f_latency_seek;
	}
};

The SoundStreamHead[2] tags define a sound effect which is to be loaded with a set of SoundStreamBlock tags. It defines the sound once and for all.

Streaming sound has a strong side effect when playing a movie: it will force a synchronization between the images and the audio. Thus some images may be dropped if the drawing isn't fast enough.

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_definefontinfo {
	swf_tag			f_tag;		/* 13 or 62 */
	unsigned short		f_font_info_id_ref;
	unsigned char		f_font_info_name_length;
	unsigned char		f_font_info_name[f_name_length];
	if(version >= 7 && f_tag.f_tag == DefineFontInfo2) {
		unsigned		f_font_info_reserved : 2;
		unsigned		f_font_info_small_text : 1;
		unsigned		f_font_info_reserved : 2;
	}
	else if(version >= 6 && f_tag.f_tag == DefineFontInfo2) {
		unsigned		f_font_info_reserved : 5;
	}
	else {
		unsigned		f_font_info_reserved : 2;
		unsigned		f_font_info_unicode : 1;
		unsigned		f_font_info_shiftjis : 1;
		unsigned		f_font_info_ansii : 1;
	}
	unsigned		f_font_info_italic : 1;
	unsigned		f_font_info_bold : 1;
	unsigned		f_font_info_wide : 1;	/* always 1 in v6.x+ */
	if(version >= 6 && f_tag.f_tag == DefineFontInfo2) {
		unsigned char		f_font_info_language;
	}
	if(f_font_info_wide) {
		unsigned short		f_font_info_map[f_font_glyphs_count];
	}
	else {
		unsigned char		f_font_info_map[f_font_glyphs_count];
	}
};

A DefineFontInfo tag will be used to complete the definition of a DefineFont tag. It uses the exact same identifier (f_font_info_id_ref = f_font_id). You must have the corresponding font definition appearing before the DefineFontInfo since it will use the number of glyphs defined in the DefineFont to know the size of the map definition in the DefineFontInfo tag.

When it looks like it perfectly matches an existing system font, the plugin may use that system font (as long as no rotation is used, it will work fine.) It is also possible to force the use of the system font by declaring an empty ...

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_definetext {
	swf_tag			f_tag;		/* 11 or 33 */
	unsigned short		f_text_id;
	swf_rect		f_rect;
	swf_matrix		f_matrix;
	unsigned char		f_glyph_bits;
	unsigned char		f_advance_bits;
	swf_text_record		f_text_record;
};

Define an object of text so the SWF player can draw a string. The only difference between the DefineText and DefineText2 tags is that the latter supports RGBA colors. This can be seen in one of the swf_text_record structures.

Since version 8 it is possible to define extraneous parameters when defining a CSMTextSettings tag referencing a DefineText or DefineText2.

struct swf_definefont {
	swf_tag			f_tag;		/* 10 */
	unsigned short		f_font_id;
	/* there is always at least one glyph */
	f_font_glyphs_count = f_font_offsets[0] / 2;
	unsigned short		f_font_offsets[f_font_glyphs_count];
	swf_shape		f_font_shapes[f_font_glyphs_count];
};

It is common to use the DefineFont tag in order to create an array of shapes later re-used to draw strings of text on the screen. Note that the definition of the shape within a font is limited since it can't include any specific fill and/or line style. Also, each shape is assumed to be defined within a 1024x1024 square. This square is called the EM Square. Fig 1. below shows you the EM Square and how it is used. The characters baseline can be placed anywhere within the EM Square (it certainly can be outside too if you wish?!?).

struct swf_rect {
	char align;
	unsigned		f_size : 5;
	signed twips		f_x_min : f_size;
	signed twips		f_x_max : f_size;
	signed twips		f_y_min : f_size;
	signed twips		f_y_max : f_size;
};

The rectangles are very well compressed in an SWF file. These make use of a 5 bits size which specifies how many bits are present in the following four fields. Don't forget that the bits are read from the MSB to the LSB and in big endian like when multiple bytes are necessary.

struct swf_setbackgroundcolor {
	swf_tag			f_tag;		/* 9 */
	swf_rgb			f_rgb;
};

This tag is used to specify the background color. It should always be included at the start of every .swf file (after the FileAttributes and Protect tags). Only an RGB color can be used (i.e. there is no alpha channel for that color, whatever the SWF version.)

To create a Flash animation that's transparent (so we can see the website gradient, for example) you use the wmode parameter in the HTML tag with the value "transparent", in which case the background color will be ignored and replaced by a fully transparent background. For example:

<embed width="440"  ...

Most of the tags will use sub-structures that are common to multiple tags. These are defined in the pages listed below.

struct swf_jpegtables {
	swf_tag			f_tag;		/* 8 */
	unsigned char		f_encoding_tables[<variable size>];
};

The JPEGTables tag is used to define the encoding tables of the JPEG images defined using the DefineBitsJPEG tag.

There can be only one JPEGTables tag in a valid SWF file. And it should be defined before any DefineBitsJPEG tag.

The content of this tag is the JPEG encoding tables defined by the 0xFF 0xDB and 0xFF 0xC4 tags. The f_encoding_tables buffed must start with 0xFF 0xD8 (SOI) and end with 0xFF 0xD9 (EOI).

Note that the player of SWF better enforces the correctness of this tag since version 8.