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Optimizing Isadora® for Speed

There are many factors that influence Isadora’s video processing speed, including the speed and type of your processor, amount of RAM installed on your computer, hard disk speed, the format in which the video files are stored, and several other factors. This section details several tips to help you get the very fastest frame rates from Isadora.

Tip 1: Use the fastest computer you can

Much of the code inside Isadora is optimized for these the SSE / Altivec processors that are part of most contemporaray Intel or PowerPC chips. Using these processors will result in significant speed increases when compared to G3 or non-MMX processors.

Tip 2: Add as much RAM (Random Access Memory) to your computer as possible.

Modern MacOS and Windows computers use a feature called “virtual memory”. When the computer senses that some data that resides in your computers RAM (i.e., the extremely fast internal memory linked to your processor) has not been used for a while, it will write it out to disk to make more RAM available to other applications. This is called “page swapping” and can adversely affect performance.

The best way to solve this problem is to add more RAM to your computer. As a general rule, 512 megabytes is a good amount. 1 Gigabyte is even better. Page swapping will often take place on a 128-megabyte machine with more than one application running.

Tip 3: Don’t run other applications at the same time as Isadora

Every running application consumes system resources. So, especially when using Isadora for a live performance, don’t run any other applications at the same time. Even if they aren’t “doing anything” they get some of the processor’s time, and thus slow down Isadora.

Tip 4: Store Video Files at a resolution of 320 x 240 or 400 x 300

A full sized frame of Digital Video has a resolution of 720 x 480. That’s a total of 345,000 pixels that each video effect must process – a substantial number for even the fastest computers. By reducing the resolution of your movies to one-half (i.e., 320 x 240) you reduce the number of pixels that must be processed by 75%, resulting in an equivalent speed up in processing.

You may also have noticed that 360 is exactly half of 720 (the standard DV-NTSC width), so why not store your movies with a horizontal resolution of 320 and not 360? This is because you want the “aspect ratio” (the ratio of width to height) of the video image and the output device (i.e., a video monitor or video projector) to match. The aspect ratio of a DV frame is 3 to 2, while a second monitor or projector attached to your computer will almost always have an aspect ratio of 4 to 3. A video with a resolution of 320 x 240 has an aspect ratio that matches the output device, allowing Isadora to use optimized code to render the image to the screen.

If you would like to have a bit more resolution, you can compress your movies at 400 x 300. But this means that you should also set your output device to 800 x 600 to get the highest rendering speed (see below.)

You can use a number of software tools to convert your 720x480 DV-NTSC files to a 320 x 240 format. But perhaps easiest is the Pro edition of Apple’s QuickTime Player. See Tip 10 for instructions on how to use QuickTime Player to compress your video.

Tip 5: Compress your video files using the Photo JPEG codec.

In addition to changing the resolution of your files, recompressing them with the Photo JPEG codec (compressor/decompressor) offers further speed improvements when playing video from your hard drive. While the files will not be as small as with other codecs, the Photo JPEG compressor offers several advantages. The first, and most important, that it requires less processor power to decompress the images when compared to many other codecs. Secondly, it is enhanced for the G4 processor on Macintosh computers (many other codecs are not.) Third, because each frame is compressed as an individual picture, it is very fast when jumping to an arbitrary location within the clip (i.e., when using the position input of the Movie Player) and it plays just as well backwards as forwards.

You can use a number of software tools to convert recompress your files using the Photo JPEG codec But perhaps easiest is the Pro edition of Apple’s QuickTime Player. See Tip 10 for instructions on how to use QuickTime Player to compress your video.

Tip 6: Set the resolution of your output to an even multiple of the video being processed by Isadora, and use the ‘direct’ option in the Projector.

When the resolution of the output device (i.e., the second video output on your computer) is an exact multiple of the video being sent to it, Isadora uses highly optimized code to render the video. If the video images being processed have a resolution of 320 x 240, setting the output resolution to 640 x 480 (i.e., exactly double in both dimensions) allows Isadora to use this special code. If you render your movies at 400 x 300, set your video output to 800 x 600 to enable this optimized code.

IMPORTANT: To take advantage of this feature, you must set the ‘mode’ input on your Projector actor to ‘direct’. The ‘mode’ input is set to ‘copy’ by default because ‘direct’ works on almost every computer, but not absolutely every one.

Tip 7: When capturing live video, set the Video Capture Size to Half and make sure the Force 4:3 Aspect Ratio menu item is checked.

For the same reasons listed above, having the live video appear at half resolution makes everything run faster. To do this, from the Capture menu choose Video Capture Size > Half. Turning on the Force 4:3 Aspect Ratio ensures that the live video is in the same ratio as the recorded clips, again saving processing power.

Now, on some cameras (notably the Apple iSight) the resolution of the camera is actually double that of a DV Camera. (You can see this by looking at the image in the Video Preview window.) In this case, you may need to set the Video Capture Size to Quarter.

Tip 8: Turn off the Video Capture when you’re not using it.

The Capture Control actor in Toolbox Group 7 allows you to turn live video on and off from within an Isadora scene. If you are not using live video in a section of your piece, then use this actor to turn it on and off at the appropriate moment.

Note, however, that turning on the live video capture can take as long as 1/3 of a second, and this may result in a visible glitch in your video output.

Tip 9: If you only need to capture video and not sound, then use Start Video Only Capture and vice-versa.

If you only need the video coming from the camera, and not the audio (i.e., you’re not using the Sound Level Watcher or capturing live sound to disk) then just enable the video capture and not the audio capture. Similarly, if you only need the sound input but don’t need video, use the Start Audio Only Capture.

Tip 10: How to use Apple’s QuickTime Player (Pro Edition) to recompress your movies.

As mentioned above, movies stored using the Photo JPEG codec at resolution of 320 x 240 will give excellent performance when they are played back in Isadora. Below are instructions on how to use the Apple’s QuickTime Player to store your movies in this format.

You can recompress a movie to this format using QuickTime Player if you have the Pro version of QuickTime. To export a movie to the Photo JPEG format, follow the following steps:

  1. Open the movie in QuickTime Player.
  2. Choose File > Export – the Movie Settings dialog will appear. (If the Export item does not appear in the File menu, you don't have the Pro Version of QuickTime. You can purchase it for $30 from Apple Computer.)
  3. In the Export pop up menu at the bottom of the dialog, choose "Movie to Quicktime Movie".
  4. In the Use pop up menu at the bottom of the dialog, choose "Most Recent Settings".
  5. Click the Options button to show the Movie Settings dialog. Then follow these steps:

Video Section:

  1. Make sure the check box labeled "Video" at the top of the dialog is checked.
  2. Click on the Settings... button
  3. In the first pop-up menu in the section labeled "Compressor" choose Photo - JPEG
  4. In the section labeled "Quality" use the slider to set a compression factor of Medium or High. Using Medium produces somewhat smaller files, but is more grainy. Using High produces less grainy files, but they are somewhat larger.
  5. In the section labeled "Motion", make sure the edit box to the right of "Frames Per Second" has no number in it. This will cause the exported movie's frame rate to match the source movie. Note: you can choose a lower frame rate (i.e. 12 or 15, etc.) to reduce the size of the movie and increase performance – but do this only if you have problems playing movies at the normal frame rate.
  6. Click on the Size... button to show the Export Size Settings dialog box
  7. Click the button labeled "Use Custom Size"
  8. Set the Width to 320 and the Height to 240
  9. Click OK Export Size Settings dialog.
  10. Click OK in the Movie Settings dialog.

Sound Section:

  1. If your movie does not have sound, make sure the check box over the section labeled "Sound" is not checked and skip to the section below called "Saving the Movie". Otherwise, check it and follow the instructions below
  2. In the section labeled "Video" click on the Settings... button
  3. In the pop up menu labeled "Compressor" choose None.
  4. Set the Rate pop menu to 44.1 KHz
  5. Set the Size radio button to 16.
  6. Set the Use radio button to Stereo or Mono, as appropriate.
  7. Click OK

Saving the Movie:

  1. In the edit box below the text "Save Exported File As:" type the name for your new movie.
  2. Choose destination folder for your new movie using the file selector near the top of the dialog
    Click Save.

A progress dialog box will appear as QuickTime player exports your movie. When the dialog disappears, your movie is done compressing.

To see the difference in size between the original movie and the newly compressed one, do the following:

  1. Bring the original movie to the front by clicking on its window.
  2. Choose Movie->Get Info to show a window that gives information about the movie.
  3. Choose ?Movie? from the pop-up menu on the top left.
  4. Choose ?General? from the pop-up menu on the top right.
  5. Look at the ?Data Size? and ?Data Rate? in that window. Take note of the values.
  6. Close the window by clicking on its close box in the top left or by choosing File->Close.
  7. Now bring the new movie to the front by clicking on its window.
  8. Follow the same procedure starting at Step 2 to show its Data Size and Data Rate.
  9. You’ll see how much smaller the movie is and how its data rate has been lowered through the resizing and compression process.