How to Make MPEG Movies on Unix Workstations
First off, what's an MPEG?
MPEG (Moving Pictures Experts Group) is a group of people that meet under ISO (the
International Standards Organization) to generate standards for digital video
(sequences of images in time) and audio compression. In particular, they define
a compressed bit stream, which implicitly defines a decompressor. However, the
compression algorithms are up to the individual manufacturers, and that is where
proprietary advantage is obtained within the scope of a publicly available
international standard. MPEG meets roughly four times a year for roughly a week
each time. In between meetings, a great deal of work is done by the members, so
it doesn't all happen at the meetings. The work is organized and planned at the
meetings. MPEG itself is a nickname. The official name is: ISO/IEC JTC1 SC29
WG11.
ISO: International Organization for Standardization
IEC: International Electro-technical Commission
JTC1: Joint Technical Committee 1
SC29: Sub-committee 29
WG11: Work Group 11 (moving pictures with audio)
MPEG has also become a synonym for a digital computer animation. (e.g. --
"Does this site have any neat MPEGs?"). The filename suffix .mpg usually denotes
an MPEG-format animation.
You will need the following data and software tools to create an MPEG movie
on a Unix workstation:
a series of image files containing the individual frames of the animation.
A word of caution here -- the mpeg encoding process doesn't deal very well
with single-pixel wide lines or other small details. Consequently,
computer-generated images of wire-frame objects, animated graphs, etc., won't
come out quite like you expected. Natural images, sampled video, and
fully-rendered computer images will work quite well. a program -- actually, a collection of programs, NetPBM.
Netpbm is a toolkit for conversion of images between a variety of different
formats, as well as to allow a few basic image operations. The package is
intended to be portable to many platforms. It has been tested under UNIX (BSD
and SYSV, e.g. SGI, Sun4, Sun386i, DEC and Apollo DN 3500), VMS and Amiga OS.
There are also compiler directives in it for MS-DOS. NetPBM will can convert
these images into three separate Y, U and V files (Y-signal, U-signal and
V-signal dates back to early color television terminology. The Y component is
the luminance, U and V are chrominance.) The mpeg encoding process
subsequently works with the luminance information at full resolution, and the
chrominance information at reduced resolution (the reason why single-pixel
lines don't look right). an MPEG encoder that will assemble all the Y,U,V files into a single
animation file (.mpg). A popular, public domain, encoder, Mpeg, and its related
documentation, is available on the web (Note: you may want to browse the
directories a level up from the converters for other interesting items). There
was an MPEG video research group (the Portable Video Research Group) at
Stanford University in the early 1990's. I can't find pointers to their
work, but copies of it exist elsewhere. Download the
PVRG MPEG encoder, CV 1.2.2, a colormap conversion utility that is necessary to use the PVRG encoder,
and download a
PVRG technical report
that describes MPEG-1 video and their software. an MPEG display program to view the results. The most common player for
Unix platforms is mpeg_play,
also in the public domain and freely available.
NOTE: A new web resource for all things MPEG and related is now available at:
www.mpeg.org .
Image data files
The image data files can be in any of the most common
image formats (.rle, .sgi, .ppm, .gif, .ps, .tiff, .xwd, .jpg, and .tga) Using
available public-domain conversion tools such as netpbm, command lines or
scripts can be used to convert them to ppm format and then to YUV files. It is
often desirable to scale the image data down to a relatively small size (about
320 pixels by 240 pixels maximum, 160 pixels by 120 pixels preferred, especially
if you are intending to provide access to the animations on the Web.) This is
done so that the resulting movie will play back at a reasonable speed and be a
manageable size. The MPEG encoding process works best with image dimensions that
are even multiples of 16.
Converting to YUV
The image data is first converted to a .ppm (portable
pixmap file format) format using the appropriate converter for the image data
format. For example, if the images are in .gif form, the converter "giftopnm"
should be used. In a similar fashion, .tga format images (Targa) would be
converted using "tgatoppm". No matter what image format the data is currently
in, before sending it to the MPEG encoder, it must be converted into separate Y,
U and V files. One way to do this is to use the program ppmtoyuvsplit (which is
part of NetPBM.)
Here is an example of a simple script that will process all the .gif image
format files in the current directory and create the appropriate Y, U, and V
files:
#!/bin/csh -f
foreach file (*.gif)
set outf=$file:r
giftopnm $file | ppmtoyuvsplit $outf
end
MPEG Encoder
The commonly-used MPEG encoder for Unix platforms is
mpeg. It process a series of Y,U,V files and assembles an .mpg
file as output. The basic form of the mpeg command and options
is:
mpeg [-d] [-NTSC] [-CIF] [-QCIF] [-PF] [-NPS] [-MBPS mbps] [-UTC]
[-XING] [-DMVB] [-MVNT]
[-a StartNumber] [-b EndNumber]
[-h HorizontalSize] [-v VerticalSize]
[-f FrameInterval] [-g GroupInterval]
[-4] [-c] [-i MCSearchLimit] [-o] [-p PictureRate]
[-q Quantization] [-r Target Rate]
[-s StreamFile] [-x Target Filesize] [-y]
[-z ComponentFileSuffix i]
ComponentFilePrefix1 [ComponentFilePrefix2 ComponentFilePrefix3]
As you can see, there are a lot of specifications that require some
familiarity with image compression terminology and techniques. A simpler
approach is provided by the script, "makempeg" from the
folks at the University of Minnesota. The script combines the conversion from image file format to
Y,U,V with the necessary mpeg arguments. Basically, you start with a bunch of
image files, then invoke makempeg, which does all the work.
makempeg.1
makempeg - create an mpeg movie file from a series of
image files
SYNOPSIS
makempeg [ -fs start_frame_number ] [ -fe end-
ing_frame_number ] [ -fi frame_increment ] [ -base name ]
DESCRIPTION
This command can be used to generate an mpeg movie.
Before attempting to run this command, make sure you have
the following:
When run, this command will make two passes over the data.
The first pass involves converting the data to YUV format.
The second pass takes the YUV data and encodes it into an
mpeg stream. The entire process may take a great deal of
time depending upon the size and number of images.
OPTIONS
-fs start_frame_number
Use this option to specify the starting image frame number. Default: 1
-fe ending_frame_number
Use this option to specify the ending image frame number. Default: 1
-fi frame_increment
Use this option to specify the frame increment if other than the default of 1.
-base name
Use this option to specify the base name of the image files. Default "image"
EXAMPLES
makempeg -fs 1 -fe 100 -base truck
From the series of image files named truck.0001.rle to truck.0100.rle, make an mpeg movie file named truck.mpg.
IMAGE SIZES
While mpeg movies can be made from images of any size,
images whose X and Y dimensions are evenly divisible by 16
are preferred. If the source images are originally sized
for the Abekas A60 (720x486) and were generated using
Wavefront software, an image size of 384x288 would work
well. If the source images are originally sized for the
are a couple of examples showing how to resize an image
using various commands:
An Abekas A60 image created by Wavefront software:
fant -S 384 288 old.rle >new.rle
pnmscale -width 384 -height 288 old.ppm >new.ppm
izoom old.sgi new.sgi .533 .593
An Abekas A60 image NOT created by Wavefront software:
fant -S 400 272 old.rle >new.rle
pnmscale -width 400 -height 272 old.ppm >new.ppm
izoom old.sgi new.sgi .556 .560
IMAGE FILE FORMAT
This command expects two things of the image files provided:
they must be named using the following convention:
they must be in one of the following image file formats:
NOTE: "base" is any name you choose for these image files.
"xxxx" is a four digit number padded with zeros. While an
mpeg movie file can be made from images of any size, it is
wise to keep the images small so that the movie can be
played back at a reasonable speed. An image size of about
400x272 is suggested.
Here is an example of how you might convert and scale a
series of image files for use with makempeg.
@ i = 1
foreach file (*.sgi)
set out = `echo $i | awk '{printf "image.%04d.sgi",
$1}'`
echo Converting $file to $out...
izoom $file $out .556 .560
@ i++
end
SUFFICIENT DISK SPACE
makempeg generates a lot of temporary files.
AUTHOR
Wesley C. Barris (wesb@msc.edu)
Army High Performance Computing Research Center (AHPCRC)
Minnesota Supercomputer Center, Inc.
Please send questions or suggestions about this web page to:
sp@rcc.its.psu.edu
ASET | ITS | Penn State
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