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Modifying Clips

Sooner or later, footage will be captured incorrectly, imported wrong, or just plain need modification. There will be lots of times when you'll need to break the rules (such as when dealing with overcranked footage). This section explains exactly how to make important changes to how your footage plays back and is used.

Adjusting Audio Channels

As you learned in Chapter 3, Adobe Premiere Pro has what you may be used to—mono tracks. But equally important, it also has stereo tracks and 5.1 tracks. A stereo track is a single track where you'd put a stereo clip, or music.

You may be familiar with other editorial tools that use a pair of tracks to handle stereo (usually a pair of mono tracks). A cool feature of Adobe Premiere Pro is that you're able to handle the audio easier because it's a single unit.

Switching stereo (or 5.1 clips) to mono

Of course, what can happen accidentally is that a clip is detected or captured as stereo. To fix it, all you have to do is choose Clip > Modify > Audio Channels and change the track format to Mono (FIGURE 4.18). You'll then have two discrete tracks with individual gain and panning abilities.

Figure 4.18

Figure 4.18 Choose Clip > Modify > Audio Channels to change the audio information. Just remember that if the audio clip is being used in a Timeline, Adobe Premiere Pro won't let you change it!

Switching mono clips to stereo

You may be in a situation that's opposite of the previous scenario: A clip you're using has two discrete channels and you want them to behave like a stero clip. Not a problem; just choose Clip > Modify > Audio Channels and change the track format to Stereo.

Forcing stereo or mono on import

When you import audio, Adobe Premiere Pro automatically assigns the type of audio. This happens based on the Audio Preferences. You can resolve 99 percent of improper audio imports by setting Adobe Premiere Pro's Preferences correctly.

  1. Choose Premiere Pro > Preferences > Audio (Mac OS) or Edit > Preferences > Audio (Windows).
  2. Set the audio to the proper type—Mono or Stereo—depending on how you want Adobe Premiere Pro to interepret your audio.

    In situations in which you are bringing in music or used a stereo microphone, set the preference to Stereo.

    In situations in which you're bringing in audio with multiple mono tracks, such as an interview where each person has a microphone, set this preference to Mono.

Interpreting Footage

There are some very good reasons for interpreting your footage. They include graphic files or footage that is missing a flag for pixel aspect ratio correction or correctly removing extra frames from 24p material.

Of course, anytime you monkey with the way that Adobe Premiere Pro interprets the footage (FIGURE 4.19), you're taking the chance that your footage might not look right. Choose the wrong setting and your alpha channel may be reversed or a video file won't play back due to an incorrect frame rate.

Figure 4.19

Figure 4.19 The Interpret Footage dialog allows you to modfiy the way Adobe Premiere Pro handles your clips. Be careful; there is no easy reset.

But sometimes you'll have to tweak these settings, if, for whatever reason, they were interpreted incorrectly.

For this exercise, we'll use a new project file. Choose File > Open, navigate to Chapter Files > Chapter_04_Media > [Version Number], and open the project Ch04_Importing.Media.prproj.

Assigning a frame rate

The footage frame rate is set in the camera, but the sequence frame rate is set by you when you create it. You can of course cut footage of differing frame rates together into the same sequence, and Adobe Premiere Pro will automatically blend the frames so the proper speed is maintained.

But what if that's not what you want? Perhaps you shot footage at 60 frames per second to conform it to play back at 30 frames per second. This technique only works with cameras that have a high frame rate (like 720p60 cameras). Otherwise, your best bet is to choose Clip > Speed/Duration to change the speed of the clip, which is mentioned in Chapter 7. With this technique, you'll get a nice, slow-motion effect.

Let's slow down a clip that has been shot at 60 frames per second.

  1. Open the sequence 01 Frame Rate.
  2. Play back the footage and observe the speed of the biker.
  3. Choose Clip > Modify > Interpret Footage (FIGURE 4.20).
    Figure 4.20

    Figure 4.20 The Interpret Footage dialog with the speed changed to 29.97.

  4. Select the "Assume this frame rate" option and enter 29.97 frames per second.
  5. Click OK.
  6. Drag the right edge of the clip to extend the shot.
  7. Watch your sequence to see the impact of the frame rate change.

Interpreting pixel aspect ratio

There are headaches and then there are Headaches. When your files have the wrong pixel aspect ratio, they will look distorted. Computers have square pixels; the height and width are the same. Video pixels are often non-square; that is to say, they have a different width than height. Being able to interpret non-square pixels correctly is a technical necessity because so many cameras can shoot multiple sizes and frame rates (while preserving affordable recording options).

You'll see non-square pixel aspect ratios most often in standard definition files. Both widescreen (16x9) and "normal" (4x3) video files have the same number of pixels. It's the shape of the pixels that makes the difference. The 16x9 pixels are wider (and hence fill out the television frame).

The pixel aspect ratio information is stored in the raw media file. When interpreted incorrectly, it looks like FIGURE 4.21.

Figure 4.21

Figure 4.21 Both clips are the same video. The pixel aspect ratio of the one in the Source Monitor (left) is incorrectly interpreted, whereas the shot in the Program Monitor (right) is correct.

Let's fix a clip that's incorrectly flagged as square pixels.

  1. Open the sequence 02 PAR. The sequence contains two clips. The green clip is being interpreted correctly as having a widescreen DV pixel aspect ratio. The Red clip is not.
  2. Play the sequence and compare the frame sizes.
  3. In the Footage – Incorrect bin select the clip PAR.mov.
  4. Choose Clip > Modify > Interpret Footage.
  5. Click the Pixel Aspect Ratio Conform To button and choose the D1/DV NTSC Wide-screen 16:9 (1.2121) option.
  6. Click OK. The footage conforms to the correct pixel aspect ratio and fills the frame.
  7. Watch your sequence to see the impact of the change.

Field order

Video can be recorded in fields, usually 1/60 or 1/50 of a second apart. They're stored together as a single frame. The term for this is interlacing. Although interlacing is a depreciating technology, you'll still encounter it.

Should Adobe Premiere Pro store the field order (and retrieve it) as the first field, the top field? Or should the field order be retrieved by the second field (lower field) first? Some cameras shoot progressive where both fields are shot at the same time and stored together to make up a frame.

Generally, unless you're shooting progressive, high definition is generally upper field first. Video is generally lower field for standard definition. If you see "tearing" or "sawtooths" when you play back the video, that's usually a sign of a field problem. It's easiest to see when the video is output on a broadcast monitor. Another way to view symptoms of field problems is to blow up the footage to 100 or 200 percent (FIGURE 4.22).

Figure 4.22

Figure 4.22 At 200 percent blowup, the field tearing is visible for the clip in the Record Monitor on the right. This tearing is an artifact of improper interpretation. The correctly interpreted shot on the left, in the Source Monitor, looks correct.

Let's fix a clip that's incorrectly flagged with the wrong field order.

  1. Open the sequence 03 PAR. The sequence contains two clips. The green clip is being interpreted correctly as having an upper field first; the second is reversed field order.
  2. Click the panel menu in the upper-right corner of the Program Monitor panel and make sure the Display Both Fields option is selected.
  3. Play the sequence and compare the field orders.

    It is easiest to see wrong field order on an interlaced display. If you only have a computer monitor or laptop screen, it may be difficult to see the problem.

  4. In the Footage – Incorrect bin select the clip Field_Order.mov.
  5. Choose Clip > Modify > Interpret Footage.
  6. Select the Field Order Conform radio button and choose the Lower Field First option.
  7. Click OK. The footage conforms to the correct field order.
  8. Watch your sequence to see the impact of the change.

Alpha channels

Alpha channels determine the visibility of parts of a clip. However, transparency can be confusing due to how the term alpha channel is used. The term alpha channel is used when it's on a clip, but when you view only the alpha channel, it's typically called a matte.

Two alpha channel settings are available in Adobe Premiere Pro:

  • Ignore. This option disables the alpha channel (meaning no transparency).
  • Invert. This option can be used if the transparency is reversed; you'll see the background, not the foreground (FIGURE 4.23).
    Figure 4.23

    Figure 4.23 When the alpha channel is reversed, as in this example (a figure is animated on a gold background), you see the background, not the element.

Let's fix a clip that has its alpha channel incorrectly inverted.

  1. Open the sequence 04 Alpha.

    The sequence contains two clips. The green clip is being interpreted correctly, but the red clip has the transparency reversed.

  2. Play the sequence and compare the alpha channels.
  3. In the Footage – Incorrect bin select the clip Alpha.mov.
  4. Choose Clip > Modify > Interpret Footage.
  5. Select the Alpha Channel option and deselect the Invert Alpha Channel option.
  6. Click OK. The footage shows the correct areas of transparency.
  7. Watch your sequence to see the impact of the change.

Modifying Timecode

Modifying the timecode means the clip will no longer line up with the original media it was sourced from, making it nearly impossible to retransfer or recapture. So, be careful when you do this.

However, you might want to modify timecode for a couple of reasons: to sync by timecode or to assign timecode to a clip like a DSLR clip or an audio track meant to be used in multicamera editing.

To modify the timecode, follow these steps.

  1. Select any clip in the Project panel.
  2. Choose Clip > Modify > Timecode.
  3. Enter the new timecode, and then select Set at Beginning or Set at Current Frame (FIGURE 4.24).
    Figure 4.24

    Figure 4.24 The Timecode adjustment window. Be aware that when you modify the timecode, you may be causing a mismatch if you ever need to relink to the nonmodified original source.

  4. Click OK to make your adjustment.
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