About Importing Audio Files

Final Cut Pro allows you to import audio files from other music and sound editing applications, as well as audio from audio CDs.

When you import audio files into Final Cut Pro, you need to make sure that their settings match your sequence settings. If your audio clips’ settings don’t match the sequence settings, you can still edit with them, but Final Cut Pro does real-time conversion which reduces overall playback performance.

For more information about digital audio, see Audio Fundamentals.

What Kinds of Audio File Formats Can Be Imported?

Final Cut Pro allows you to directly import any audio file format compatible with QuickTime. However, only uncompressed file formats should be used for editing.

Recommended Audio File Formats

For best performance, use one of the following uncompressed audio file formats when editing in Final Cut Pro:

  • AIFF or AIFC containing uncompressed audio

  • WAVE or Broadcast Wave Format (BWF) containing uncompressed audio

  • Sound Designer II

  • Single-track or multitrack QuickTime movies containing uncompressed audio

Natively, Final Cut Pro captures to QuickTime movie files with one or more audio tracks.

Audio Formats to Avoid

The following formats and audio data formats should be avoided when editing in Final Cut Pro because they require real-time processing for playback:

  • Any file containing compressed formats such as MP3, AAC, and Apple Lossless Codec

  • QuickTime movies containing compressed audio, such as MPEG-4 and H.264 files

  • Multiplexed video and audio streams such as MPEG-2 program streams and DV Stream files (This is one of the formats iMovie can create during capture.)

Choosing Audio File Sample Rate and Bit Depth

Final Cut Pro can import audio with any bit depth and sample rate supported by QuickTime and Mac OS X Core Audio. Final Cut Pro performs real-time bit depth conversion and sample rate conversion when your audio file settings don’t match your sequence settings. However, less processor power is required when your audio file settings and sequence settings match.

Common sample rates and bit depths used in the video industry are:

  • 32 kHz/12-bit: Consumer mini-DV camcorders can record four channels of audio using these settings. This is not recommended for most productions.
  • 44.1 kHz/16-bit: Audio CDs and consumer DAT recorders use these audio settings.
  • 48 kHz/16-bit: DV, HDV, and DVD all use these audio settings.
  • 48 kHz/20-bit: Some professional video devices record natively in this format.
  • 96 kHz/24-bit: These settings are becoming increasingly popular for professional sound and music production, although most video formats still record with 48 kHz.

For more information, see Audio Fundamentals.

Choosing Sequence Bit Depth

The bit depth setting in the Sequence Settings window determines the bit depth whenever you output or export your sequence. However, sequence audio is always mixed using 32-bit floating-point values.

Note: The Aud Format column in the Browser and Item Properties window always shows the internal mixing bit depth of a sequence, whereas the Sequence Settings window shows the bit depth used if the sequence is exported.

Mixing Sample Rates and Using Real-Time Sample Rate Conversion

Ideally, the sample rate and bit depth of your audio files should match that of your sequence settings. When you play a sequence in Final Cut Pro, any audio files with sample rates that don’t match your sequence sample rate are converted in real time. This is known as sample rate conversion, and it requires additional processing power. Clip items that require real-time sample rate conversion appear with a green render bar within the clip item. For more information, see Rendering and Video Processing Settings.

Even though Final Cut Pro can perform real-time sample rate conversion, conversions can reduce your audio mixing and effects performance. The quality of this conversion is controlled by the Audio Playback Quality setting in the General tab of the User Preferences window. Higher quality conversions reduce the number of audio tracks that Final Cut Pro can mix together in real time.

If the sample rates of all the audio in your sequence match, sample rate conversion is not necessary and the number of audio tracks that can play in real time increases. If you are working with someone who is creating music or audio files specifically for your project, you can request audio files at the settings you need to match your sequence.

However, If your audio clips don’t match your sequence settings, you can improve audio playback performance by converting your audio files to the sample rate and bit depth of your sequence.

Converting Audio Clips to Match Sequence Settings

If you are working with preexisting audio material, such as music from audio CDs, you need to convert the audio files so they match your sequence settings. For example, if you plan to use a lot of sound effects or music from audio CDs (which have a sample rate of 44.1 kHz) in a DV sequence with a sample rate of 48 kHz, it’s a good idea to convert your audio files to a sample rate of 48 kHz.

Most professional video formats, including DV, have a sample rate of 48 kHz and a bit depth of 16 (this is often abbreviated as 48 kHz/16-bit). Since these settings are so common for video post-production, they are used for most sequences in Final Cut Pro.

Important: DV sequences sometimes use 32 kHz/12-bit settings, but these settings are not recommended. As long as you don’t record your DV footage using 32 kHz/12-bit, you should not use these settings for your sequence.

Audio files can be converted using the Export Using QuickTime Conversion command.

To convert a CD audio file so it matches your sequence settings
  1. Select a sequence, then choose Sequence > Settings.

  2. Check the sample rate of the sequence in the Audio Settings area of the General tab, then click OK.

    For DV sequences, the sample rate is usually 48 kHz.

  3. Select an audio clip in the Browser that you want to convert to a new sample rate.

  4. Choose File > Export > Using QuickTime Conversion.

  5. Choose AIFF from the Format pop-up menu.

  6. Click Options.

  7. In the Sound section of the Movie Settings dialog, click Settings.

  8. In the Rate pop-up menu, choose the sample rate of your sequence, then click OK.

    Make sure the size is kept at 16-bit.

  9. Click OK.

  10. Choose a name and location for the new file, then click Save.

    Once the conversion is complete, you need to import the new media file into Final Cut Pro.

  11. In the Finder, navigate to the location of your newly converted audio media file, then select the file and drag it into your project in the Final Cut Pro Browser.

    You may want to delete the old clip in your project so you aren’t confused by two clips with the same name.

Tip: You can also convert multiple clips at once using the Batch Export command.

Importing Broadcast Wave Files

The Broadcast Wave Format (BWF) is an extension of the WAVE file format that includes additional metadata. Because BWF files can store timecode information, this format is particularly popular for video post-production. Many professional audio recorders today can record BWF files.

BWF files store only the first timecode number; the remaining timecode numbers are calculated by Final Cut Pro. Mapping timecode to audio samples is a straightforward process for frame rates such as 25 fps and 30 fps, but the process is more complex for 29.97 fps video. There are two complications:

  • 29.97 fps video is not really 29.97 fps, but rather 30 fps x 1000/1001, or 29.9700299700299700 fps (repeating).

  • There is no fixed relationship between the number of samples and the number of frames per second. Instead, a repeating sequence of varying samples per frame is established, defined by SMPTE standards.

Also, there is no ratified standard to indicate or detect whether a BWF file was recorded with drop frame or non-drop frame timecode.

To import 29.97 fps BWF files with drop frame timecode
  1. Choose Final Cut Pro > User Preferences, then click the Editing tab.

  2. Choose Drop from the NTSC Default Timecode pop-up menu.

If you have already imported BWF files with non-drop frame timecode and you want to modify the timecode to drop frame, you can use the Modify Timecode command.

To modify the timecode of a BWF file to drop frame
  1. In the Browser, select the audio clip whose timecode you want to modify.

  2. Choose Modify > Timecode, then choose Drop Frame from the Format pop-up menu.

About Broadcast Wave File Timecode at a Video Rate of 29.97 fps

If you import the same BWF file into Final Cut Pro and other editing applications, certain timecode numbers may be calculated differently. This section explains how Final Cut Pro accurately calculates timecode when importing BWF files.

In Final Cut Pro, three factors affect the calculated timecode value of an imported BWF file:

  • The true frame rate of NTSC video

  • Mapping audio samples to video frames

  • Drop frame indicators in BWF files

The True Frame Rate of NTSC Video

Timecode calculation is fairly straightforward, with the exception of NTSC-related frame rates. Calculating timecode for NTSC video is complicated because its true frame rate is not simply 30 fps, nor is it 29.97 fps. The actual frame rate is 30 fps x 1000/1001, which equals 29.9700299700299700 fps (repeating). Timecode calculated using 29.97 fps (instead of 30 fps x 1000/1001) can be inaccurate, especially as the duration of media increases. Final Cut Pro uses the more accurate calculation (30 x 1000/1001).

Mapping Audio Samples to Video Frames

Timecode is calculated for digital audio files by mapping a certain number of audio samples to each video frame. When the sample rate is an integer multiple of the video frame rate, the timecode count can be accurately mapped to the sample count. For example, if the audio sample rate is 48,000 Hz and the video rate is 25 fps, every 1920 audio samples is equivalent to one video frame.

However, with NTSC-related video rates, there is no simple relationship between the number of audio samples per second and video frames per second. To avoid ambiguity, the Society of Motion Picture and Television Engineers (SMPTE) specifies how many audio samples should be mapped to each video frame. The number of audio samples per frame is varied on a frame-by-frame basis to form a consistent pattern. Instead of an exact number of samples per frame, a consistent pattern of varying samples is spread over several frames.

When you import a BWF file, Final Cut Pro calculates timecode based on two parameters:

  • The editing timebase (frame rate) of the currently selected sequence preset

  • The audio sample rate of the imported BWF file

When the sequence preset frame rate is 29.97 fps and the sample rate of the BWF file is defined in the SMPTE specification, Final Cut Pro uses the repeating frame pattern defined in the SMPTE specification.

Drop Frame Indicators in Broadcast Wave Files

There is no ratified standard to indicate or detect whether a BWF file was recorded with drop frame or non-drop frame timecode. Although there are several de facto ways this information is stored, Final Cut Pro does not support reading this information. Instead, Final Cut Pro always calculates non-drop frame timecode for BWF files. You can enforce drop frame timecode during import or by using the Modify Timecode command. For more information, see Importing Broadcast Wave Files.

Using Audio CD Tracks in Your Project

Mac OS X recognizes each track on a standard audio CD as an individual AIFF file. These files can be copied directly from a CD to your hard disk and then imported into Final Cut Pro without any conversion.

Files copied from an audio CD have a sample rate of 44.1 kHz and sample size (bit depth) of 16 bits. If you’re working with a DV sequence, you can convert the sample rate using Final Cut Pro. For more information, see Converting Audio Clips to Match Sequence Settings.

Important: Do not import clips from a CD or DVD directly into Final Cut Pro. These clips will go offline as soon as you eject the disc from the drive. Make sure you copy the files to your hard disk before importing them.