Apple Compressor 3 - Manual (Page 159)

• Audio: Use this pop-up menu to choose from the four audio bit-rate options listed
below.
• None: Use this option to exclude audio from the output media file.
• 24 Kbps: Creates an audio bitstream at 24 Kbps for the iPhone (Cellular) device option.
• 128 Kbps: Creates an audio bitstream at 128 Kbps.
• 256 Kbps: Creates an audio bitstream at 256 Kbps.
• Frame Sync: Also known as the key frame interval, the Frame Sync value represents how
often a key frame is inserted in the H.264 stream. The lower the number, the more
smoothly the video can be manipulated (scrubbed) during playback (more frequent
key frames). The higher the number, the more efficient the compression (less frequent
key frames). The available range is from 2 to 10 seconds; the default is 5 seconds.
The Frame Sync setting also has an Automatic button. Clicking the Automatic button
causes the encoder to choose a frame sync rate that matches the source video file.
• Multi-pass: Similar to two-pass MPEG-2 encoding, multi-pass offers the best possible
quality. For faster (single-pass) encoding, turn this feature off by deselecting the
checkbox.
Note: If you are also using distributed processing, you may want to turn off job
segmenting. For more information, see
Job Segmenting and Two-Pass or Multi-Pass
Encoding .
• Include AAC Audio: Use this checkbox to include a stereo AAC audio track in the output
movie. The audio track will have a bit rate of 128 kbps. The sample rate will be either
44.1 kHz or 48 kHz, depending on the input audio.
159 Chapter 12 Creating H.264 for Apple Devices Output Files