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.) This alpha channel is compressed using the ZLIB scheme as defined with the DefineBitsLossless image formats and appears at the end.
With Flash 10, DefineBitsJPEG4 was introduced to support a deblocking filter parameter. This parameter should be set to a value between 0.0 and 1.0 (0x0000 and 0x0100--so really a value from 0 to 256 inclusive.)
WARNING: These tags require you to save the swf_tag in long format (i.e. f_tag_and_size & 0x3F == 0x3F even if the size is smaller.)
f_encoding should include 0xFF 0xDB and 0xFF 0xC4 entries.
The f_image_data buffer should include the 0xFF 0xE0, 0xFF 0xC0 and 0xFF 0xDA.
Since Flash 10 the f_encoding and f_image_data fields defined in the DefineBitsJPEG2, DefineBitsJPEG3 and DefineBitsJPEG4 tags, are viewed as one single large buffer and thus it can be a verbatim JPEG, PNG or GIF89a file.
When the buffer represents a JPEG, it starts with 0xFF 0xD8 and ends with 0xFF 0xD9.
When the buffer represents a PNG, it starts with 0x89 0x50 'P' 0x4E 'N' 0x47 'G' 0x0D '\r' 0x0A '\n' 0x1A '^Z' 0x0A '\n'.
When the buffer represents a GIF89a, it starts with 0x47 'G' 0x49 'I' 0x46 'F' 0x38 '8' 0x39 '9' 0x61 'a'.
|WARNING:||Up to Flash 7, both buffers (f_encoding and f_image_data) need to start with a 0xFF 0xD8 (SOI) and end with 0xFF 0xD9 (EOI). Since Flash 8, this practice should not be used anymore.|
The f_alpha buffer is compressed with ZLIB as defined in the DefineBitsLossless tag (this is similar to the PNG format). WARNING: this field only works with JPEG data. A PNG or GIF89a cannot make use of this field (but they can make use of their own alpha channel.)
|Note:||The Flash 10 documentation says that the f_alpha field is optional. This means you can save a JPEG in a DefineBitsJPEG4 without the Alpha Channel but still make use of the deblocking filter parameter. Before Flash 10, use DefineBitsJPEG2 instead (safer).|
The DefineBitsJPEG tag may fail if it includes any encoding tables. These tables shall be defined within the JPEGTables instead.
Note that the Adobe SWF player better enforces the correctness of these tags since version 8. Some older movies may not work properly with Flash Player 8+.