Creating a movie is at least a two step process. First you need to create the individual frames that will comprise your movie. You then need to combine these images to create a movie that you and others can play back on a computer. Almost all computer-generated movie formats use a compression algorithm. Compression is necessary because of size constraints (size of image times the number of the images to make a movie (30 frames per second) equals hundreds to thousands of megabytes). The MPEG-1 standard is one movie format that supports a very good compression scheme. Others possible formats are Apple's QuickTime, and Microsoft's AVI. This page focuses on MPEG because most platforms support MPEG-1 players and there are lots of plug-ins available for web browsers.

When you decide to make your movie, be prepared to spend more time on creating the movie than you first thought or you would like to. Movie making is an art. There is no cookbook that will tell you exactly what you need to do to create your perfect movie. Factors that contribute to the problem is that the final movie size may be the most important factor to one user, another user is more interested in the highest-quality image, and yet another is interested in portability.

If you are interested in learning more about video and various standards like MPEG, check out the web and books and magazines on video, it's creation, and deployment. Click here to go to the official web site of the Movie Picture Experts Group (MPEG).

• It is best to create the images in the correct size to begin with. Most movie creation programs do a poor job of changing size, especially the PC programs we tried. If you need to modify the size, do it before you create the movie, using tools such as imscale ('module load imtools'). NOTE: Many movie making methods expect the image size in x and y to be in multiples of 16. If not, depending on the version of mpeg_encode and mediaconvert, they will either resize the images, core dump, or complain and not create the movie.

• Most of the encoding programs expect the files to be numbered sequentially (e.g., mpeg_encode and many PC programs). A correct numbering sequence is: file0000.jpg, file0001.jpg, ..., file1000.jpg. An incorrect sequence is: file1, ..., file10, ..., file100 (because using the wildcard symbol (*) will not sort them correctly).

• Even though the various MPEG encoders can generate movies with various frame sizes, not all viewers can handle them. For example, we had problems viewing the movie on a PC with a 1037x541 movie. We have been successful with movies of 640x480 or 320x240.

• Keep your frames uncluttered, especially if you are creating a movie with small frames (e.g. 320 x 240 movie).

• Avoid thin lines (example movie), dark blue lines on a black background (example movie), highly saturated colors, small objects, etc.

• Start with a good image. Any compression scheme will degrade the quality of the original.

• Before creating all your frames, you might want to try making a sample movie from a few frames. This is important because your time-step between frames may be too great, and when played back this creates a jittery movie. Also, while the individual frames may look great, motion can add visual artifacts that are both confusing and distracting.

• Don't create your frames using the GIF file format. GIF compresses the color information to 256 colors. MPEG does not have this restriction. Use JPEG, TIFF, PNM, or another file format that the mpeg encoder supports. Also, do not use an image file format that does a lossy-compression on the image.

Creating Movies

SGI tools: available on escher.nersc.gov and LBNL SGI's.

mediaconvert , a GUI to dmconvert(see below).

makemovie, dmconvert, commnand-line movie makers.

Visualization Packages that provide MPEG generators.

idl mpeg generation.

avs/express mpeg generation.

Unix tools: available on escher.nersc.gov and LBNL sytems mounting the Software Farm.

mpeg_encode.

Try out the different programs to see which one creates the movie quality and size you want. Here are two sample movies that show how the two encoders worked with small bouncing balls with their default settings for compression. In this case, mediaconvert did a better job than mpeg_encode but created a larger file (490K versus 90K). mpeg_encode did a better job when the balls were made a little larger and the colors were de-saturated. Movie 1, notice the balls are not distorted. Movie 2, the balls are distorted.

With both encoders you can play with changing the compression scheme by modifying the number of I, P, and B frames. The definition of these frame types are detailed at the Berkeley site mentioned in the previous paragraph or any article on MPEG. Basically, the more B and P frames you specify, the more compression.

Displaying Movies

SGI tools: available on escher.nersc.gov and LBNL SGI's.

movieplayer displays MPEG-1, QT, AVI movies.

mpeg_play  displays MPEG-1 movies on a Unix system.

Advanced Tips

• Depending on what you want to do with your movie, you might want to play with the Bit Rate found on the "Video Output Parameters" sub-menu of mediaconvert) or the "BIT RATE" line in the mpeg_encode parameter file. You can decrease the size of your movie file if you lower the bit rate. This might be important if you are playing this movie across the network.
• Sometimes you cannot create your images without jagged edges or small dropouts in the frames. mediaconvert has the ability to do some image processing (smoothing) on the individual tool images before the movie is made. You access this capability by selecting video parameters from the main menu and then selecting the "MPEG-1 Settings Panel". "Prefiltering" has three options: None for no smoothing (Sample Movie), Medium does some smoothing, and Maximum does the most smoothing (Sample Movie). Check out the smoothing flags to see which one works best on your frames. Note: Smoothing will increase the size of your movie file.
• Mediaconvert lets you specify the frame rate of the movie. Remember that film is 24 frames/second, while video is 29.97 frames/second. If you start with a 30 fps movie and you have the Frame rate is set to 24, you will get an MPEG-1 movie with fewer frames. mediaconvert is preserving the duration of the movie (important in non-computer generated movies) and converting from 30 to 24 fps. Thus, a movie with less frames.
• Sometimes you need to concatenate two or more images into one frame. Useful tools for doing this are Imtools and pbmplus.

Useful tools for image manipulation

• Imtools is a suite of very useful tools from SDSC (available on NERSC escher.nersc.gov).

imconv is useful to converting from one image file format to another.

imscale is good for changing the size of the image and changing the image format.

imstoryboard is useful to change the size, image format, and add margins.

An example of how to use imconv to convert from a TIFF file to a JPEG file:

module load imtools
imconv 0000.tif 0000.jpg

• On NERSC (escher.nersc.gov) and LBNL machines you can convert your CGM movie file (called gmeta in this example) into JPEG files all at once by doing

module load ncar
ncgm2jpeg gmeta

• xv is very useful for displaying an image, converting a single image's format, and for checking on the dimensions of x and y. (Available on NERSC and LBNL machines, module load xv is needed in some).
• Another useful suite of tools that have similar capabilities are the pbmplus tools (module load pbmplus on escher.nersc.gov and module load graphics/pbm on LBNL).
• If you want to analyze your movie (frames, size, compression, etc.) there are two useful tools. mpeg_stat (module load mpeg_play) gives the most information about your MPEG-1 movie. SGI's dminfo gives more summary information for MPEG-1 and other movie formats.

NERSC User Training on MPEG generation: link to a presentation. [an error occurred while processing this directive]