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1993-04-27
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Short: MPEG player for ECS/AGA/OpalVision/PicassoII, needs 020+,2MB,OS2.04
---
mp (mpeg_play) is a MPEG software decoder for the Commodore Amiga computer. It
is derived from the UNIX/X11 MPEG decoder version 2.0 by the Berkeley Plateau
Research Group. Many thanks to Lawrence A. Rowe, Ketan Patel and Brian Smith
for publishing that decoder, without them I wouldn't even know how MPEG works.
Most work for 'mp' went into dithering and display code for the native Amiga
graphics hardware and some third party graphics boards but some friends and I
also tried to improve playback speed so that it becomes usuable on a small
computer system like the Amiga. Thanks to Urban D. Mueller who contributed an
optimized IDCT routine and gave many ideas for a fast HAM display, to Andrew Denton
and Harv Laser who tested the OpalVision support, to Ken Dyke for his nice MPEG
animations and all the net people that patiently tested each new beta ten or more
times a day and made lots of useful suggestions to improve the program.
---
Requirements for the 1.02 version:
- 68020 or higher CPU. Some thoughts went into that decision since it rules out
many people in viewing MPEGs but IMHO a 68000 is way too slow to decode MPEG at
a useful rate. Even an 68030/25MHz is quite slow, at least with this program.
- about 2MB memory. The program uses table lookups for some functions, especially
the HAM rendering code and the hybrid dithering need a large table. Other display
and dithering options can live with less memory.
- AmigaOS 2.0 or higher. Well, everyone should have updated to AmigaOS2.0.
Compatibility to AmigaOS1.3 would have added more special cases. I also
believe that people who can afford an accelerated Amiga have no problems
with that requirement and it made some functions a bit easier.
---
How to use the program:
mp has to be run from the CLI/Shell. Following the UNIX tradition it accepts
command line parameters in the form 'programname' '-option...' 'input-file'
and reads from standard input when no input filename is given. So if you
run mp without arguments it will appear to do nothing. But in reality it
tries to read an MPEG bitstream from the keyboard. Since that is a bit difficult
to enter you should end input by hitting CTRL-\ which sends an EOF condition.
valid options are:
-display displayname this has no function and is a remnant from the X11 code
that allowed to specify the name of the X server/screen
to use.
-dither dithermode selects a dither and/or display mode. Some displays types
need special dithering so this has been combined into one
option. More about the possible dithermodes below.
-loop causes the player to repeat an animation for ever. You have
to break it with CTRL-C.
-eachstat this would produce verbose statistics information. Calculating
the statistics however slows down the player and thus has been
#ifdef'ed out.
-no_display dithers, but does not display, usually used for testing and
timing purposes.
-shmem_off again a remnant of the X11 player with no function
-quiet the program normally writes the frame number for each frame
to the standard output which can be used to pause the player
by hitting any key in the shell window. The -quiet option
suppresses that output.
-l_range num
-cr_range num
-cb_range num All paletted display modes use a 'color cube' to fill the
palette. The default is to use 16 luminance values (-l_range),
4 red values (-cr_range) and 4 blue values (-cb_range).
For some movies this can produce bad colors, you can change
the resolution of the color cube with these options, the
total number of colors however cannot be larger than 256.
-nob causes the player to ignore and not display B (bothway
interpolated) frames.
-nop causes the player to ignore and not display P (predicted)
frames.
Dither and display options:
-dither ordered use simple ordered dithering
-dither ordered2 a faster ordered dither. This is the default.
-dither mbordered ordered dithering at the macroblock level.
-dither fs4 Floyd-Steinberg dithering with 4 error values propagated
-dither fs2 Floyd-Steinberg dithering with 2 error values propagated
-dither fs2fast a faster fs2
-dither hybrid Hybrid dithering, a combination of ordered dithering for
luminance and fs2 dithering for chrominance. Errors are
not propagated properly.
-dither hybrid2 Hybrid dithering with error propagation among pixels.
-dither 2x2 A dithering technique using a 2x2 pixel area for each pixel.
The image displayed is 4 times larger than the original
image encoded. Random error terms are added to each pixel to
break up contours and gradients.
-dither gray Grayscale dithering. The image is dithered into 16 grayscales.
Chrominance information is thrown away.
-dither gray8 Grayscale dithering with 256 grayscales (AGA only).
-dither color 'True' color display with 4 bits luminance and 2*2 bits for
chrominance.
-dither ham6 'True' color display using HAM approximation. For each pixel
either red, green or blue are set correctly and the other
color components are the same as the pixel to the left. As
the name implies this uses the 6bit HAM mode and is limited
to 4096 possible colors.
-dither none no dithering is done, no image is displayed. Used to time the
decoding process.
-dither mono Floyd-Steinberg dithering in black and white.
-dither threshold Simple thresholding in black and white.
All above modes except for none, mono, threshold, gray, gray8, color and ham6 are
paletted modes. On OCS/ECS machines this will produce an EXTRA_HALFBRITE display
for the maximum number of colors. On AGA machines a 256 color screen is used which
produces a mucher better display. As written above, the gray8 mode is only available
on AGA machines. The selection between gray and gray8 is not done automatic because
the 16 graylevel mode is somewhat faster and some AGA users might want to trade
display quality for speed.
The player supports two 24bit displays: the OpalVision board and the PicassoII
graphics board. The options
-dither opal15 and
-dither opal24 generate a 15bit or 24bit display on the OpalVision.
Playback speed is somewhat slower than for the native
Amiga graphic. This requires the opal.library to be
present in the LIBS: directory.
-dither village24 generates a 24bit display on the PicassoII board. This
requires the PicassoII software to be installed properly.
You don't need to redirect the Workbench to the PicassoII
board nor use the ChangeScreen commodity as the player
directly talks to the PicassoII driver software.
Example:
mp -dither ham6 jet.mpg
will play back the MPEG movie from the file jet.mpg and use a HAM display.
mp -loop -dither village24 micky.mpg
will play back the file micky.mpg endlessly on the PicassoII board until
CTRL-C is hit.
---
Playback speeds:
MPEG is a very CPU intensive way of compressing and decompressing digital
video data. An Amiga A3000 achieves a rate of about 3 frames per second for
average MPEG streams of 160x120 pixels per frame that were encoded with
the XING encoder. Better _encoders_ can get better compression and streams
from these encoders can be played back a bit faster.
MPEG movie | Resolution | Compression ratio | Frame rate
----------------------------------------------------------------------------
micky.mpg | 160x120 | 19.4 | 2.92
moglie.mpg | 160x120 | 23.8 | 2.93
flight.mpg | 160x120 | 20.8 | 2.92
birdisba.mpg | 160x120 | 27.6 | 3.53
BigE_accel.mpg | 176x144 | 41.1 | 3.14
tennis.mpg | 352x240 | 30.5 | 0.83
jet.mpg | 128x96 | 48.3 | 5.84
The frame rates were measured on an A3000/25MHz with static column RAMs on
a PAL monitor. NTSC machines may show slightly different timing due to different
frame times (50Hz vs. 60Hz) and the need to synchronize a double buffered display.
---
This version of the player (1.02) has been finished at the Amiga User Meeting in
Illertissen/Germany on April 23-25th 1993. The length of the executable is
108596 Bytes and yields the VERSION string:
mpeg_play 1.02
(Illertissen Version)
Please send any suggestions and bug reports to me. I can be reached via E-Mail
as mlelstv@mpifr-bonn.mpg.de. People with Internet access can also find me often
in the IRC (Internet Relay Chat) channels #amiga and #amigager.
Michael van Elst