Apple Final Cut Pro 7 - Manual (Page 381)

• 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.
381 Chapter 26 Importing Media Files into Your Project