Information Technology (9626) | Video and audio editing

Study Notes: Chapter 11 - Video and Audio Editing (AS Level)

Welcome to Chapter 11! This topic is incredibly practical—it’s about turning raw footage and sound into polished, professional products. Mastering video and audio editing is essential not just for your Paper 2 practical exam, but also for countless modern IT applications, from marketing to education. Let's dive into the tools and techniques you need!

11.1 Video Editing: Manipulating the Visual Story

Video editing is the process of manipulating and rearranging video shots to create a new, coherent work. You must be able to perform specific tasks to meet audience and application requirements.

The Basics of Clip Manipulation

These actions focus on getting your timing and structure right:

• Trimming: Removing unwanted footage from the beginning or end of a single video clip. (Think of trimming the ends of your hair—you’re just neatening up the edges.)
• Splicing/Joining: Connecting two or more separate video clips together to form a sequence.
• Altering Clip Speed: Changing how fast or slow a clip plays (e.g., creating slow-motion or fast-forward effects).
• Setting an Aspect Ratio: Defining the proportional relationship between the width and the height of the video frame (e.g., 16:9 for widescreen, 4:3 for older TVs). This is crucial for matching the output medium.

Quick Review: The primary goal of basic manipulation is structuring the narrative and ensuring the video fits its destination screen size.

Visual Enhancements and Effects

Once the structure is built, you add effects to improve flow and visual quality.

• Adding Transitions: Effects placed between clips to smoothly move from one scene to the next. (Examples include fades, dissolves, or wipes.)
• Adding Fading Effects: Specifically, Fading In (video gradually appears from black or white) or Fading Out (video gradually disappears). This usually signals the beginning or end of a sequence.
• Adding Pan and Zoom Effects: Moving the camera view horizontally (pan) or magnifying the shot (zoom) across a static image or video frame. This is often used on still images to bring them to life.
• Using Filters and Colour Correction: Adjusting the overall look, brightness, contrast, and colour balance to achieve a specific mood or correct poor lighting conditions.

Working with Text and Still Images

Text elements convey information, while still images can be used for impact or context.

• Adding Titles, Subtitles, and Captions: Text displayed on screen to introduce sections, clarify speech, or provide location details.
• Creating Credits: Listing the people and sources involved. For scrolling credits, you must ensure readability of text and use appropriate blank lines so the viewer can follow the information easily. You must also include appropriate source information (where footage/music came from).
• Inserting a Still Image: Placing a static photograph within the video timeline.
• Extracting a Still Image: Taking a single frame from the video clip to use as a standalone image (e.g., a thumbnail).
• Resizing and Cropping: Adjusting the dimensions of the still image, often specifically to match the video’s aspect ratio, preventing distortion.

Did you know? The "Pan and Zoom" effect is sometimes called the Ken Burns effect, named after the American documentary maker who popularised the technique of slowly panning and zooming across archival photographs.

Integrating and Managing Audio

Audio is essential for engagement and context.

• Adding Audio: Importing music, sound effects, or voiceovers onto the timeline.
• Editing Audio within a Video Clip: Adjusting the volume, applying fades, or synchronising the sound within that specific clip.
• Removing Audio: Deleting the original sound track associated with the video clip (e.g., if you only need the visuals).

11.2 Video Output and Compression

The final stage is producing the video in a format suitable for its intended destination.

Exporting and File Formats

You need to export the video in a specific format compatible with where it will be viewed (the media).

• Exporting Formats (Key ones to know):
  • MP4 (.mp4): Extremely common, good balance of quality and small file size. Ideal for internet and mobile streaming.
  • AVI (.avi): Older, high quality, but typically results in very large files (often uncompressed or minimally compressed).
  • MOV (.mov): Developed by Apple, high quality, popular for professional editing.
  • WMV (.wmv): Windows Media Video, often used for Windows-based systems.
• Advantages/Disadvantages of Export File Formats: Consider factors like file size, quality, platform compatibility (will it play on Apple/PC/mobile?), and ease of streaming.

Video Compression and Resolution

Compression reduces file size, but you must consider its effect on quality.

• Compressing a video to different resolutions: Adjusting the dimensions (e.g., 1920x1080 to 640x480). This suits different media:
  • DVD: Needs specific standard definition resolutions.
  • Internet Streaming: Often requires higher resolution (e.g., 1080p).
  • Mobile Devices: Needs lower bitrates and resolutions to ensure smooth playback on smaller screens with slower connections.
• Effects of different methods of compression on video quality:
  • High compression usually means a smaller file but a noticeable reduction in video quality (e.g., blocky artifacts or loss of fine detail).
  • Less compression retains quality but results in a larger file size.

Key Takeaway (Video): Video editing is about precision (trimming, splicing), presentation (titles, transitions), and production (choosing the right format and resolution for the final delivery platform).

---

11.3 Audio Editing: Shaping the Soundscape

Just like video, audio requires specific tools to sound professional and meet application requirements.

Audio Editing Tools and Techniques

• Importing New Tracks: Bringing external audio files into your project.
• Adding a Track: Creating a new layer in your editing software specifically for a piece of audio (like background music or a voiceover).
• Trimming and Splicing: Cutting off unnecessary audio sections and joining different clips together (same principles as video).
• Fading In and Fading Out: Gradually increasing or decreasing the volume at the start or end of a clip for smooth transitions.
• Altering Clip Speed/Changing Pitch: Speeding up or slowing down the audio. Changing the pitch alters how high or low the sound is. Note that changing speed often affects pitch unless specifically compensated for.

Enhancing and Adjusting Audio Quality

These techniques help create a cleaner, more engaging sound.

• Normalising an Audio Clip: Adjusting the volume of the entire clip so the loudest peak reaches a specified maximum level. This makes the overall track louder without distortion (clipping). This process often includes removing any DC offset (a vertical shift in the audio waveform that can cause pops/clicks).
• Applying Noise Reduction: Using software tools to remove unwanted background sounds (hiss, hum, static).
• Applying Equalisation (EQ): Adjusting the balance between frequency components (e.g., boosting low pass filters to remove high-pitched hiss, or using high pass filters to remove low rumbling sounds).
• Adding Delay/Echo and Reverberation:
  • Delay/Echo: Distinct repetitions of the sound.
  • Reverberation (Reverb): A dense collection of reflections that simulate a space (like a hall or a small room).
• Overdubbing: Adding a new recording over existing audio, such as recording a voiceover after the main video is complete.
• Changing from Stereo to Mono: Converting two audio channels (left and right) into a single channel. This reduces file size and ensures compatibility on systems without stereo playback.

Encouraging Phrase: Don't worry if 'DC Offset' or 'Equalisation' sound tricky. In practice, editing software makes these actions easy—you just need to remember what they achieve (cleaner, balanced sound).

11.4 Audio Output and Compression Theory

Understanding how digital audio works is vital for managing file quality and size.

Sampling Rate and Resolution

Audio file sizes are heavily determined by two factors related to converting analogue sound to digital data:

• Sampling Rate: This is the number of times per second the audio waveform is measured and converted into digital data. Measured in Hertz (Hz) or Kilohertz (kHz).

  Why is it important? A higher sampling rate means more accurate sound reproduction, but a larger file size.

• Sampling Resolution (Bit Depth): This is the number of bits used to store the amplitude (loudness) of each sample. (e.g., 8-bit, 16-bit, 24-bit).

  Why is it important? Higher resolution means a greater dynamic range (difference between quietest and loudest possible sound) and higher fidelity, but also a larger file size.

Therefore, file sizes depend directly on sampling rate and sampling resolution.

Audio Compression and Formats

Compression is needed to reduce large files for streaming or storage on small devices.

• Exporting Audio Formats (Key ones to know):
  • WAV (.wav): Uncompressed or losslessly compressed. Excellent quality, large file size.
  • MP3 (.mp3): Most common format. Uses lossy compression. Small file size, acceptable quality for music/speech.
  • MP4a (.m4a) / AAC: Advanced Audio Coding. Often used by Apple. Provides better quality than MP3 at the same bit rate. Uses lossy compression.
• Lossy vs. Lossless Compression:
  • Lossless: Retains all original data. File size reduction is minimal (e.g., WAV, FLAC).
  • Lossy: Permanently discards some data considered less important to human hearing. File size reduction is significant (e.g., MP3, AAC).
• Files vs. Containers: Some formats (like MP4) are containers. They hold both video and audio tracks, which can be compressed differently. The format refers to the wrapper, while the compression method (codec) dictates quality.

Key Takeaway (Audio): Audio editing ensures clarity (normalising, noise reduction) and ambience (reverb, echo). The file size and quality depend fundamentally on the sampling rate and resolution chosen during export, and whether lossy or lossless compression is applied.