7. Encoding with MPEG-4 and H.264

The MPEG-4 codec in Compressor comes in two versions: Part 2 and Part 10 (more commonly known as H.264). To prevent confusion, in this book MPEG-4 Part 2 will be referred to as MPEG-4, and Part 10 will be called H.264.

MPEG-4 Encoding

MPEG-4 is most commonly used to encode content destined for Internet distribution. It encodes very quickly compared with H.264, and manages the compromise between file size and image quality intelligently and efficiently. In addition, MPEG-4-encoded media is a good choice for playback on portable devices like video iPods and mobile phones.

Encoding for the Web requires some planning related to the target audience. If you need to distribute files for dial-up-modem users, for example, your settings will be quite different from the settings you’d use to deliver the same content to broadband users. A movie’s data rate is the main setting that determines playback suitability within a given bandwidth. Data rates are defined in kilobits per second (Kbps); this should not be confused with kilobytes (KB), the measurement that refers to a movie’s file size. An MPEG-4-encoded movie might have a data rate of 100 Kbps and occupy 2000 KB (2 MB) of disc space, for example.

The following table lists the most common target bandwidths and their delivery medium:

Encoding MPEG-4 Video

In the Inspector window, the Encoder pane divides settings into three tabs: Video, Audio, and Streaming. The easiest way to create a custom preset for encoding MPEG-4 is to duplicate an existing Apple preset. In the Presets window, select an Apple preset that is close to your target bandwidth and duplicate it (see Lesson 3). Compressor will place the copy in the Custom folder.

Here are some tips for Web encoding:

• When selecting frame rates, choose a multiple of the source media’s frame rate. If the source frame rate is 30 frames per second (fps), a choice of 5, 10, or 15 fps is acceptable. (Round 29.97 fps up to 30 fps and 23.98 fps to 24 fps.) Choosing frame rates that are not multiples can produce choppy playback.

• When working with keyframes, find a value that offers the best quality at the smallest output file size. If the source media content changes quickly from frame to frame, try a lower number. If the source is primarily static, increase the value.

• Constant Bit Rates offer more direct control when targeting a specific bandwidth. Variable Bit Rates offer greater quality more efficiently, but the output file size and bandwidth will vary depending on the source media.

Note

The Bit Rate field and slider will be shadowed when any of the VBR options are chosen from the Bit Rate pop-up menu.

Encoding MPEG-4 Audio

The MPEG-4 presets in Compressor use AAC for the compression of source audio. See Lesson 6 for more detailed information regarding AAC audio in MPEG-4 containers.

Additional MPEG-4 Settings

MPEG-4 Encoding for Video iPods

Apple’s video iPods will play media encoded with MPEG-4. Create a custom preset based on the following parameters to achieve smooth iPod playback:

H.264 Encoding

H.264 embodies a significant leap in compression technology. Compared with its MPEG-4 predecessor, H.264 scales much more efficiently, delivering up to four times the frame size at a comparable data rate, and achieves similar quality at almost one-third the data rates needed for MPEG-4.

The disadvantages of the H.264 codec are longer encoding times, greater processing demands for playback, and compatibility issues for distribution (on a Mac, QuickTime 7 is required for H.264 playback).

Encoding H.264 Video

Compressor has two Inspector-window interfaces for H.264 modification. One interface controls the settings for HD disc encoding (see Lesson 5), and the other interface controls the creation of QuickTime container files using H.264. When producing files for Web delivery, use QuickTime movie presets instead of the presets designed for HD discs.

More Info

As with MPEG4, H.264 employs an interframe compression scheme. Keyframes contain complete image data and Delta frames contain interpreted image information between the keyframes. Frame reordering allows the Delta frames to look to any keyframe in the movie for relative information, which allows H.264 to very efficiently encode high-quality media. The multi-pass feature lets the H.264 codec intelligently determine keyframe frequency and bandwidth when those options are set to Automatic.

The Quality slider and Data Rate settings work together to encode the video. Use the following table to determine the best settings:

Note

The Quality sliders can be fine-tuned to any value along the continuum.

Encoding H.264 Audio

H.264 can use any QuickTime-compatible audio codec. The highest-quality encoder available to Compressor is AAC.

H.264 Encoding for Video iPods

The Apple preset for video iPod encoding uses H.264 as the video codec and AAC as the audio codec. The specifications are strict for iPod compliance when using H.264. Therefore, you should apply the Apple preset instead of creating a custom iPod preset, because the preset will consistently produce the best results.