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DMPEG V1.0
Public Domain MPEG decoder
by Stefan Eckart
0. Features
===========
DMPEG/DMPLAY is another MPEG decoder/player for the PC:
- decodes (nearly) the full MPEG video standard
(I,P,B frames, frame size up to at least 352x240 supported)
- saves decoded sequence in 8 or 24bit raw file for later display
- optional on-screen display during decoding (requires VGA)
- several dithering options: ordered dither, Floyd-Steinberg, grayscale
- color-space selection
- runs under DOS, 640KB RAM, no MS-Windows required
- very compact (small code / small data models, 16 bit arithmetic)
- real time display of the raw file by a separate player for
VGA and many Super-VGAs
1. Introduction
===============
This program is similar in concept to MPEG386 (a port of the Berkeley player
by Greg Ennis, see appendix) which was posted a while ago. DMPEG, however,
works also for fully fledged MPEG files and is not based on the Berkeley
decoder. It is very compact and somewhat optimized for a 16 bit architecture
but still much slower than the Xing Decoder. Therefore I hesitate to call it
a real-time decoder, although it can decode directly to the screen (and to a
file in parallel). I suggest to use this program in addition to Xing's
MPEG.EXE 320x200 DOS player. The latter is appropriate for real-time display
of '160x120, I-frame only' Xing files, DMPEG is more suitable for larger size
'real' MPEGs containing I, P and B type, 352x240 sized frames or for faster
and better quality 'off-line' display of the 160x120 MPEGs. Try it on one of
the larger MPEG files (see appendix, my recommendation: flowg.mpg) to see
that MPEG can also be used (and is intended) for storing really sharp,
virtually noise-free sequences.
To give an impression of the attainable speeds, here are some figures
measured on a 386DX/33 with 4MB RAM and a Conner 3104 100 MB hard disk. The
decoding time for flowg.mpg (352x240) was about 7 sec per frame, 18 minutes
for 150 frames. waterski.mpg (also 352x240, but lower quality) required
only 3.5 sec per frame. A decoded 150 frame raw data file is 12 MB long and
can be displayed at 5.2 frames/s. 160x120 MPEGs reach 22 frames/s while the
decoding time is 1.9 s/frame. The display frame rate is limited by the
transfer speed from hard disk to memory (about 550 kByte/s on my PC). If you
have enough RAM, you can obtain much higher speed by playing from a large
RAM-disk (e.g 23 frames/s for a 352x240 sequence).
This program is Public Domain and I don't take any responsibility regarding
its fitness, usefulness etc. (#include <your_favourite_disclaimer>).
This software is not related to my employment at the Technical University
of Munich. Comments, bug reports, questions to:
Stefan Eckart
Kagerstr. 4
W-8000 Muenchen 80
Germany
email: stefan@lis.e-technik.tu-muenchen.de
2. Usage
========
dmpeg [options] input.mpg [output.raw]
input.mpg any MPEG DIS 11172 compliant non multiplexed compression layer
stream (D frame streams unsupported)
output.raw the decoded and dithered 8 or 24bit raw output file;
if omitted: output to screen only
Options:
-q quiet mode; no text output (except error messages)
-v verbosity level; can be increased by repeating this option;
enables display of decoded information (start codes,
frame size, quantization scales etc.), can't be combined with
the -s option
-dx dithering options:
-d0 ordered, saturation dominant 4x4 dither (default)
-d1 Floyd-Steinberg error-diffusion / blue-noise-shaping (2 weights)
-d2 Floyd-Steinberg error-diffusion / blue-noise-shaping (4 weights)
-d3 undithered grayscale output
-d4 24 bit true color output
-p0 use full color range palette
-p1 use restricted color range palette (default)
-s display the decoded image (or its top left part if larger
than 320x200) on a standard VGA while decoding
Options can be combined. Example:
dmpeg -d2s flowg.mpg flowg.raw
decodes MPEG file flowg.mpg to raw file flowg.raw using FS4 dithering and
displaying it on the screen.
dmpeg -vvv flowg.mpg flowg.raw
as above but using ordered dither and printing much information on
startcodes, headers and parameters.
3. The decoded file player
==========================
This is a rather simple program for transferring the decoded file to the
screen. It currently supports 8 bit files only (no HiColor/TrueColor).
Usage:
dmplay [options] input.raw
input.raw the raw date file to be played
Options:
-sx select video driver (x=0..10):
-s0 standard VGA or Super-VGA in 320x200x256 mode (default)
-s1 VESA
-s2 ET4000
-s3 ET3000
-s4 Video 7
-s5 Paradise
-s6 Trident
-s7 Chips & Technologies
-s8 ATI
-s9 Orchid
-s10 Oaktech
-dn delay (0..65535, default 0)
-b 8 bit transfer (default: 16 bit)
All SVGA drivers use the 640x480x256 display mode and require at least
512 kB of video memory. If your graphics card is not listed, the
best you can do (besides trying all drivers in the hope that one of
them might work) is to obtain a VESA BIOS extension for your card
and use mode -s1. A collection of such drivers had been posted to
comp.binaries.ibm.pc some two months ago and is also available at
ftp.rahul.net:/pub/bryanw/pc/vesadrv2.zip (anonymous ftp).
All drivers except the standard VGA, ET4000 and the VESA driver in
conjunction with the mentioned public domain VESA BIOS extension TSR for the
ET4000 are untested. I'm very interested in email feedback which drivers
work and which don't.
The -d option controls playback speed. It is implemented as a simple delay
loop without synchronization to a timer or vertical retrace.
The -b option is probably superfluous. I don't have much experience in PC
graphics programming and since I saw some example driver routines using
bytewise transfer (rep movsb) instead of wordwise (rep movsw) I preferred to
include this as a fudge factor. You should try it only in case of problems.
Speed is reduced considerably upon activation of this switch (at least for
cards with 16 bit bus interface).
Display can be controlled with the following keys:
any key except
space, return
or escape halt display at current frame and step one frame forward
each time a key is pressed
space step one frame backwards
return continue display
escape quit program
4. Technical information
========================
The player is a rather straightforward implementation of the MPEG spec [1].
The IDCT is based on the Chen-Wang 13 multiplication algorithm [2]
(not quite the optimum, I know). Blocks with not more than eight non-zero
coefficients use a non-separated direct multiply-accumulate 2D-IDCT
(sounds great, doesn't it?), which turned out to be faster than a 'fast'
algorithm in this (quite common) case. Dithering is pretty standard. Main
difference to the Berkeley decoder (except for the fewer number of supported
algorithms) is the use of 256 instead of 128 colors, the (default) option to
use a restricted color-space and the implementation of a color saturation
dominant ordered dither. This leads to a significantly superior quality of
the dithered image (I claim, judge yourself).
Restricted color-space means that the U and V components are clipped to
+/-0.25 (instead of +/-0.5) and the display color-space points are distributed
over this restricted space. Since the distance between color-space points
is thus reduced by a factor of two, the color resolution is doubled at the
expense of not being able to represent fully saturated colors.
Saturation dominant ordered dither is a method by which a color, lying
somewhere between the points of the display color space, is approximated
by primarily alternating between two points of constant hue instead of
constant saturation. This yields subjectivly better quality due to the
lower sensitivity of the human viewing system to saturation changes than
to hue changes (the same reasoning as used by the PAL TV standard to improve
on NTSC). The improvement is particularly visible in dark brown or redish
areas.
5. File formats
===============
If you want to write your own player or to post-process the results, here is
the format of the 8 bit raw file:
Byte
0..7 compatibility bytes (to be ignored)
8..9 image width (MSB first)
10..11 image height (MSB first)
12..31 compatibility / unused
32..799 color table, R[0],G[0],B[0], ... R[255],G[255],B[255]
800.. image data in natural order (top left to bottom right,
all frames concatenated without any gaps or repeated
headers)
The format of 24bit true color files (-d4 option) is:
0..7 compatibility bytes (to be ignored)
8..9 image width (MSB first)
10..11 image height (MSB first)
12..31 compatibility / unused
32.. image data (3 bytes per pixel: R,G,B, top left to bottom right,
all frames concatenated without any gaps or repeated
headers)
These formats happen to be compatible with the raw format used by a shareware
program called Image Alchemy. In fact you can use that program to view the
first frame of the sequence and to convert it into other formats.
6. Future
=========
Obviously this program is still in its early infancy with many improvements
to be done. I assume it to be relatively bug-free in the MPEG part, at least
it decodes all the MPEG scenes I could get hold of up to now (note that some
of the MPEGs at toe.cs.berkeley.edu seem to contain errors, e.g. bicycle.mpg,
which show up both on the Berkeley decoder and on DMPEG).
Some improvements which come into mind: speed-up, better graphic support
(Hi/TrueColor), better user interface, other output formats.
I hope to be able to include some of these points into a new release.
7. References
=============
1. Coding of moving pictures and associated audio for digital storage
media up to about 1,5 Mbit/s, Draft International Standard ISO/IEC
DIS 11172, 1992.
2. Chen, Wang, IEEE ASSP-32, pp. 803-816, Aug. 1984.
Appendix A: Related Software
============================
This list is probably incomplete, but it's all I'm aware of. Of course
there are programs for other systems as well (Mac, Amiga etc.).
mpeg_play MPEG Video Software Decoder (Version 2.0; Jan 27, 1993)
Authors: Lawrence A. Rowe, Ketan Patel, and Brian Smith
Computer Science Division-EECS, Univ. of Calif. at Berkeley
toe.cs.berkeley.edu:/pub/multimedia/mpeg/mpeg-2.0.tar.Z
mpgplay Online port of mpeg_play for DOS
by: Giampero Caprino, scompx@milano.oas.olivetti.com
(evaluation version, works only with Xing files)
mpeg386.exe Offline port of mpeg_play for DOS
by: Greg Ennis, 93gke@cs.williams.edu
(based on mpgplay, works only with Xing files)
mpegwin Online port of mpeg_play for MS-Windows
by: Michael Simmons, msimmons@ecel.uwa.edu.au
toe.cs.berkeley.edu:/pub/multimedia/mpeg/Ports/mpegw32.tar.Z
(HiColor & TrueColor support, Shareware)
mplay.exe,
mpeg.exe DOS MPEG players from Xing Technologies
(very high speed, but decodes only a small subset of the
MPEG standard)
? a variety of MS-Windows MPEG players from Xing Technologies
(sorry I lost the overview...)
MPEGv1.1 MPEG Software Encoder
Authors: Portable Video Research Group
havefun.stanford.edu:/pub/mpeg/MPEGv1.1.tar.Z
APPENDIX B: MPEG files
======================
Two good sources for MPEG files:
toe.cs.berkeley.edu:/pub/multimedia/mpeg/movies
havefun.stanford.edu:/pub/mpeg
High quality MPEGs you simply can't afford to miss:
tennis.mpg
flowg.mpg
bike.mpg
--
Stefan Eckart, stefan@lis.e-technik.tu-muenchen.de, April 1993.