February 12, 2007

Exporting to the iPod Using Compressor

Software used: Final Cut Studio (FCP 5, Compressor 2)
also tested on Discreet Cleaner 6 Tested on:
Power PC, Intel Core Duo, iPod Video 30 & 80

By Seth Kenlon

Exporting for the iPod Video or other portable devices is an exciting development for content providers, and is even now evolving as the "new movie theater for independent filmmakers" (Arayna Thomas, "RUNE Coming to an iPod Near You," Hollywood Reporter 19 Sept. 2006).

Final Cut Pro, and its Quicktime Pro engine, features a pre-set export function, which outputs a .m4v file that ensures the bitrates of both video and audio fall into an acceptable range for the iPod...and usually looks like an amateur encoded it.

This article will explore the process of high-quality encoding, but also upon what a professional editor can and should do in order to optimize content for iPod Video.

First, you should ensure that you are editing with proper timeline settings, and that you are keeping in mind the final resolution. Podcasts and iPod-only content rarely need to stand up to television-screen size enlargement; the delivery resolution most often will be 320x240 pixels. By making this decision early, you can maximize your bitrate in the end and minimize the bandwidth required when your audience is downloading, as well as the server space required for its hosting and archiving.

Of course, for a project intended to be watched on larger screens, the project resolution should be at least 640x480. Obviously, the resulting file size will be substantially larger, and the download time will be longer.

In either case, there is no need to letterbox within Final Cut Pro. If the footage is widescreen, leave it in its native 16:9 aspect ratio for export and let the iPod letterbox it for you.

Also, know your pixel aspect ratio. The most common for SD footage is NTSC-CCIR 601/DV but take note if you are using a different ratio.

Unlike many instances of using the "Movie to iPod" pre-set, proper encoding will not require any last-minute adjustments of contrast, brightness, or color, so the image you see in your final cut should be the image you see on the iPod after the export is done. Be sure that every frame is what you want, and for good measure it is a good idea to wrangle your white levels by using EFFECTS > VIDEO FILTERS > COLOR CORRECTION > BROADCAST SAFE.

Keep in mind, too, that on-screen elements in an iPod-viewable video will be quite small in the frame. Subtitles, on-screen signage, credits, et cetera, should be sized appropriately so that they are legible on the small screen.

Now that you have your final project ready for export, go to FILE > EXPORT > USING COMPRESSOR... Your timeline content is automatically sent to Compressor, and a batch project is created.

Here, too, there is a pre-set for iPod export, but again this produces a .m4v file and its results are unpredictable. The better choice is found by selecting your file in the batch list, and going to SETTINGS > MPEG-4 * SOURCE MATERIAL > MPEG-4 IMPROVED * FOR CD (in which * refers to your source type; 24p, NTSC, or PAL).

This pre-set will be used as a starting point only.

Be aware, also, that in the previous version of Compressor, the name of the pre-set may be different. The important thing is to locate a high bandwidth Mpeg-4 starting point.

Next, look to the Inspector window.

The first tab is the VIDEO tab. ISMA Profile should by default be set to IMPROVED. Keep that. The frame rate should be set for whatever your native frame rate has been. The only advantage to setting the end frame rate for something lower than what it was edited in is to save the end user's iPod battery (lower frame rates often maximize battery playing time), but unless your project features only basic visuals that do not require a normal video frame rate, skimping on frame rate is not advisable.

Regardless of project size or quality, a Variable Bit Rate (VBR) should always be used. This is a vital feature of Compressor, and one that lesser encoders lack. Video compressing works in part because the computer examines one frame compared to the next, and refrains from re-creating pixels that have not changed. Thus with VBR, a sequence of frames in which the only movement is a blink of an eye would be quite small, while with a Constant Bit Rate the same sequence would be unnecessarily compressed just as much as a sequence of brightly colored butterflies in a windstorm.

Whether you use HIGH VBR (being higher quality and larger file size) or LOW VBR (being lower quality and smaller file size) depends upon your desired file size as well as your own opinion of what your video demands. HIGH VBR is recommended.

The next tab, AUDIO, is easier. The iPod will not accept audio with a bitrate higher than 160kbps, so for the highest quality of audio that will be your setting.

If your project uses only simple audio and would rather reduce the file size, then by all means a bitrate of 128kbps or 96kbps can be used. For complex soundtracks obviously the higher bitrate is recommended.

The next setting is found in the GEOMETRY tab.

Your frame size depends entirely on you; as stated in the beginning of this article, for iPod-only content, 320x240 is the logical setting. For more flexibility and larger file sizes, the 640x480 is better.

Imperative for widescreen projects is the PIXEL ASPECT menu. Here you proscribe that the project is NTSC CCIR 601/DV (ANAMORPHIC).

Further, in the CONSTRAIN TO DISPLAY ASPECT menu, select your desired ratio depending on your FCP timeline setting; most typical of course is 16:9

These settings will ensure that the iPod will not play the video in a 4:3 frame but to letterbox it instead. By doing this in Compressor rather than as a nested timeline in FCP, you decrease the pixels contained within the frame and allow for a higher bitrate and/or smaller file size.

Hit SUBMIT in the batch window, and the encoding begins.

The final but most important principle in good compression is testing. It is up to you to test different compression rates and different codecs, and to record the results. Every project is unique, every video different, and so there will never be one pre-set for a truly optimized end result. The best, optimized compression is gained by frequent testing and constant exploration of available technology.

Happy encoding!

ISIS Productions, LLC is a full service film production company serving New York and LA, having produced projects with organizations such as Human Rights Watch, Catholic Big Sisters, and Columbia University. The company's first feature film, RUNE was the world's first feature film to world premier on Apple's iPod Video.


copyright © Seth Kenlon 2007

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