Technical information

by Forest Key and Chris Hock
25
Macromedia Flash MX 2004 Video FAQ
What standard is Flash Video compression based on?
Flash Video is based on the H.263 video compression standard. It’s based
on the version of H.263 dated May 1996, sometimes referred to as H.263v1.
This is distinct from the revised version of H.263, dated February 1998,
sometimes referred to as H.263v2 or H.263+.
The H.263 video format supported by Flash differs slightly from H.263. For
the most part, it is a subset of H.263, with some features removed and
others added a shown in the following lists.
The following H.263 features have been removed from the Flash Video
format:
n
GOB (group of blocks) layer
n
Split-screen indicator
n
Document camera indicator
n
Picture freeze release
n
Syntax-based arithmetic coding
n
PB-Frames
n
Continuous presence multipoint
n
Overlapped block motion compensation
The following non -H.263 features have been added to the Flash Video
format:
n
Disposable frames (difference frames with no future dependencies)
n
Arbitrary picture width and height up to 65,535 pixels
n
Unrestricted motion vector support is always on
n
A deblocking flag is available to suggest the use of a deblocking filter
Where can I get more information about the Flash Video file format?
Detailed technical information about the FLV file format is published as part
of the SWF specification at
www.macromedia.com/software/flash/open/licensing/fileformat/. An open
source implementation of the FLV video format is available at
ffmpeg.sourceforge.net/.
What are the best pixel dimensions for transporting or encoding data
based on the H.263 standard? Would there be any benefits to encoding
the video at: 128 x 96, 176 x 144, 352 x 288, 704 x 576, 1408 x 1152?
Flash Video supports an extension to H.263 that supports frames with any
dimensions. However, there is probably a small benefit to frame sizes that
are a multiple of 8 x 8 pixels.