Apply video editing techniques (trimming, splicing, titles)

Cambridge A‑Level IT 9626 – Topic 11: Video & Audio Editing

Learning Objective

Apply a full range of video‑ and audio‑editing techniques – including trimming, splicing, transitions, titles, subtitles, credits, pan‑and‑zoom, colour‑correction, speed changes, filters, still‑image extraction, adding/removing audio, and audio processing – to produce a coherent, technically sound edited video clip that meets the Cambridge AS/A‑Level specification.

1. Overview of Video & Audio Editing

Editing combines technical manipulation of media files with creative decisions that shape the final narrative. The process must consider visual parameters (aspect‑ratio, resolution, frame‑rate, colour‑depth, file format), audio parameters (sampling rate, bit depth, codec), and legal/ethical issues (copyright, fair‑use, metadata, privacy).

2. Video‑Editing Fundamentals

2.1 Visual Parameters to Set Before Editing

• Aspect‑ratio – e.g., 16:9 (widescreen) or 4:3 (standard). Determines how the picture fills the screen.
• Resolution – e.g., 1920 × 1080 (1080p) or 1280 × 720 (720p). Affects detail and file size.
• Frame‑rate – typically 24 fps (cinematic), 30 fps (TV) or 60 fps (sports).
• Colour‑depth – 8‑bit (256 colours per channel, common for H.264) or 10‑bit (1024 colours per channel, used in ProRes 422 and H.265 for smoother gradients).
• File‑format options – MP4, MOV, AVI, WMV (each with its own container and typical codecs).

2.2 Core Video‑Editing Techniques

1. Trimming – remove unwanted frames from the start or end of a clip.
2. Splicing (cutting & joining) – combine two or more clips into a continuous sequence.
3. Transitions – hard cut, fade‑in/out, cross‑fade (dissolve), wipe, slide.
4. Titles & Subtitles – opening title, lower‑thirds, on‑screen text, closed captions (SRT or embedded).
5. Credits – opening/closing credit roll, acknowledgements.
6. Pan‑and‑Zoom (Ken Burns effect) – simulated camera movement on still images or video.
7. Colour‑Correction / Colour‑Grading – adjust exposure, white‑balance, contrast, and apply a visual style or LUT.
8. Speed Change – slow‑motion or fast‑forward; time‑stretch without altering pitch (or with pitch‑lock).
9. Filters – visual effects such as blur, vignette, sharpen, or stylised colour looks.
10. Still‑Image Extraction – capture a high‑resolution frame for thumbnails or graphics.
11. Adding / Removing Audio – detach an audio track from a video clip, replace it, or add background music/effects.

2.3 Advantages & Disadvantages of Each Technique

Technique	Advantages	Potential Drawbacks
Hard Cut	Fast, keeps narrative momentum.	Can feel abrupt if not timed to action.
Fade / Dissolve	Softens scene changes, indicates passage of time.	Overuse can slow pacing.
Pan‑and‑Zoom	Adds visual interest to static images.	Excessive movement may distract.
Colour‑Grading	Creates mood, ensures consistency across clips.	Incorrect grading can make footage look unnatural.
Speed Change	Emphasises action or compresses time.	Too slow can bore; too fast can cause motion blur or audio artefacts.
Filters (e.g., blur)	Can focus attention or achieve a stylistic look.	Over‑filtering may reduce clarity.
Adding / Removing Audio	Allows clean replacement of poor‑quality sound, adds ambience.	Sync errors may arise if not carefully aligned.

3. Audio‑Editing Fundamentals

3.1 Digital‑Audio Basics

• Sampling rate – 44.1 kHz (CD quality) or 48 kHz (standard for video). Determines the highest frequency that can be captured.
• Bit depth – 16‑bit (CD) or 24‑bit (professional). Influences dynamic range and noise floor.
• Lossy vs. lossless codecs – AAC/MP3 (lossy, smaller files) vs. WAV/AIFF (lossless, larger files).

3.2 Core Audio‑Editing Techniques

1. Import & Organise – place dialogue, music, and sound‑effects on separate tracks.
2. Normalising – adjust peak level to a standard value (e.g., –3 dB) for consistent loudness.
3. Trimming & Splicing – cut out silences, join takes.
4. Fading – fade‑in/out to avoid abrupt starts/ends.
5. Speed / Pitch Change – time‑stretch without altering pitch, or pitch‑shift without changing duration.
6. Audio Effects – reverb, echo, compression.
7. Equalisation (EQ) – boost or cut specific frequency bands.
8. Noise‑Reduction – remove background hiss or hum.
9. Over‑dubbing / Voice‑over – record additional narration or replace faulty dialogue.

3.3 Why Audio Techniques Matter

Technique	Impact on Final Video
Normalising	Prevents sudden volume jumps between clips.
EQ	Clarifies speech and removes muddy frequencies.
Noise‑Reduction	Improves intelligibility, especially in outdoor recordings.
Compression	Balances dynamic range, making quiet parts audible without clipping loud sections.

4. Export, Compression & File‑Size Considerations

4.1 Common Video Formats, Containers & Codecs (Pros & Cons)

Format	Container	Typical Codec	Pros	Cons
MP4	.mp4	H.264 / H.265	Widely compatible; good quality‑to‑size ratio; supports 8‑bit and 10‑bit (H.265).	Limited colour‑depth for H.264 (8‑bit); hardware acceleration required for H.265 on older devices.
MOV	.mov	Apple ProRes 422 (10‑bit)	High quality; retains colour‑depth; excellent for intermediate editing.	Larger file size; requires more storage and faster drives.
AVI	.avi	DivX / Xvid (MPEG‑4)	Simple structure; good for legacy Windows systems.	Less efficient compression; larger files; limited support for modern colour‑depth.
WMV	.wmv	Windows Media Video 9	Optimised for Windows playback; good compression for streaming.	Less universal than MP4; colour‑depth typically 8‑bit; not ideal for cross‑platform distribution.

4.2 Common Audio Formats & Codecs (Pros & Cons)

Format	Codec	Pros	Cons
WAV	PCM (uncompressed)	Lossless, full fidelity, easy to edit.	Large file size.
AAC	AAC (lossy)	Good quality at lower bit‑rates; widely supported on mobile devices.	Some quality loss, especially below 128 kbps.

4.3 Calculating Approximate File Size

For video: File Size (MB) ≈ (Bitrate (Mbps) × Duration (seconds)) / 8

Example – 1080p H.264 at 8 Mbps for a 2‑minute clip:

• Bitrate = 8 Mbps → 8 000 kbps
• Duration = 120 s
• Size ≈ (8 × 120) / 8 = 120 MB

Adjust bitrate to balance quality against storage or upload limits.

4.4 Metadata & Legal/Ethical Considerations

• Metadata – title, author, creation date, copyright notice, keywords. Preserve or edit responsibly.
• Copyright & Fair‑Use – use only material you own or have permission for; credit sources; avoid unauthorised music or footage.
• Privacy – obtain written consent for identifiable persons, especially in interviews.

5. Comprehensive Editing Checklist (mirrors syllabus)

• ☐ Set aspect‑ratio, resolution, frame‑rate, and colour‑depth before import.
• ☐ Import video, audio, and still images; organise into bins (e.g., Interviews, B‑roll, Music, SFX).
• ☐ Create a rough cut on the timeline.
• ☐ Trim each clip to remove dead space.
• ☐ Splice clips; apply at least two different transition types.
• ☐ Add pan‑and‑zoom where static images are used.
• ☐ Perform colour‑correction for exposure and white‑balance; apply a consistent colour grade or LUT.
• ☐ Insert titles (opening, lower‑thirds) and subtitles/closed captions.
• ☐ Add closing credits with role attribution.
• ☐ Extract any required still images for thumbnails.
• ☐ Add or remove audio tracks as required; align dialogue with video.
• ☐ Apply speed changes (slow‑motion / fast‑forward) where narrative benefits.
• ☐ Apply visual filters (blur, vignette, sharpen) sparingly.
• ☐ Import audio tracks; normalise, EQ, and apply noise‑reduction.
• ☐ Trim, splice and fade audio; adjust speed/pitch if needed.
• ☐ Balance dialogue, music, and effects using audio meters.
• ☐ Review legal compliance (copyright, consent, metadata).
• ☐ Export using the appropriate format/codec; verify bitrate, resolution, colour‑depth, and file size.
• ☐ Test the exported video on target devices (desktop, tablet, smartphone).

6. Detailed Step‑by‑Step Procedures

6.1 Trimming a Video Clip

1. Select the clip on the timeline.
2. Drag the start or end handle to the desired frame, or set In/Out points with keyboard shortcuts (e.g., I / O).
3. Confirm the trim – most editors perform a ripple trim, automatically closing the gap.
4. Play back the trimmed segment to ensure narrative continuity.

6.2 Splicing & Adding Transitions

1. Position the playhead at the cut point where two clips should join.
2. Choose a transition from the Effects panel (hard cut, fade‑in/out, cross‑fade, wipe, slide).
3. Drag the transition onto the cut or double‑click to apply the default.
4. Adjust the duration by dragging the edges of the transition icon on the timeline.
5. Preview; fine‑tune timing if the visual or audio flow feels abrupt.

6.3 Adding / Removing Audio from a Video Track

1. Right‑click the video clip and choose Detach Audio (or similar command).
2. The audio appears on a separate track; you can now mute, delete, or replace it.
3. To add new audio, import the file and place it on an audio track, aligning it with the video.
4. Use waveform view to synchronise dialogue or music precisely.
5. Apply fades or volume keyframes to avoid abrupt starts/ends.

6.4 Speed Change (Slow‑Motion / Fast‑Forward)

1. Select the clip and open the Speed/Duration dialog.
2. Enter a percentage (e.g., 50 % for half‑speed, 200 % for double‑speed) or a new duration.
3. Enable Maintain Audio Pitch if you wish to keep dialogue natural.
4. Render a preview; adjust as needed to avoid choppy motion.

6.5 Applying Visual Filters

1. Select the clip and open the Effects panel.
2. Choose a filter (e.g., Blur, Vignette, Sharpen) and drag it onto the clip.
3. Adjust parameters (radius, intensity, centre point) in the effect controls.
4. Use keyframes if you want the filter to change over time.
5. Preview to ensure the effect enhances rather than distracts.

6.6 Adding Titles, Subtitles & Credits

1. Open the “Titles/Graphics” panel.
2. Select a preset (Opening Title, Lower‑Third) or create a custom text box.
3. Enter the required text; choose a legible sans‑serif font, appropriate size, and high‑contrast colour.
4. Place the title on a video track above the footage at the correct timecode.
5. For subtitles/closed captions, either import an SRT file or use a dedicated subtitle track; ensure precise sync with dialogue.
6. For credits, use a scrolling credit roll preset; set duration (10–15 s) and list all contributors.
7. Preview to verify that text does not obscure important visual information.

6.7 Pan‑and‑Zoom (Ken Burns Effect)

1. Select a still image or a video clip.
2. Enable the “Motion” or “Pan‑and‑Zoom” controls.
3. Set start and end positions (e.g., start full‑frame, end zoomed to a focal point).
4. Adjust the duration to match the accompanying narration or music.
5. Preview; ensure the movement is smooth and purposeful.

6.8 Colour‑Correction & Grading

1. Open the colour‑correction panel (e.g., Lumetri Colour).
2. Adjust Exposure and Contrast to achieve a balanced histogram.
3. Set White‑Balance (temperature & tint) so whites appear neutral.
4. Apply a consistent Look / LUT for grading if a specific mood is required.
5. Check skin tones and key colours across all clips for continuity.

6.9 Still‑Image Extraction

1. Move the playhead to the frame you wish to capture.
2. Use “Export Frame” or “Grab Still” (usually Ctrl + Shift + E).
3. Choose a lossless format (PNG or TIFF) and a resolution matching the project settings.
4. Save with a descriptive filename (e.g., “Scene3_Thumbnail.png”).

6.10 Audio Normalising, EQ & Noise‑Reduction

1. Select the audio track; open the “Audio Effects” panel.
2. Apply “Normalize” – set peak level (e.g., –3 dB).
3. Insert an “EQ” effect; boost 2–4 kHz for speech clarity, cut below 80 Hz to remove rumble.
4. Apply “Noise‑Reduction” – capture a noise print from a silent segment, then reduce the identified noise by 10–15 dB.
5. Listen to the processed audio; toggle the effect on/off to ensure improvement without artefacts.

6.11 Exporting the Final Video

1. Open the Export/Render dialog.
2. Choose the required container and codec (e.g., MP4 + H.264, MOV + ProRes 422, WMV + WMV9).
3. Set video parameters:
   • Resolution = 1920 × 1080 (or as specified)
   • Frame rate = 30 fps (or as specified)
   • Colour‑depth = 8‑bit (H.264) or 10‑bit (ProRes/H.265)
   • Bitrate = 8–10 Mbps for high‑quality web delivery; increase for archival quality.
4. Set audio parameters:
   • Codec = AAC 256 kbps (stereo) for most deliveries, or PCM WAV for lossless master.
5. Enable “Render at Maximum Depth” and “Use Hardware Encoding” if available.
6. Specify output filename and destination folder; include relevant metadata.
7. Click “Export” and monitor the render progress.
8. After export, play the file on target devices to confirm quality, sync, and file‑size compliance.