Cambridge A Level Information Technology (ICT): Video and audio editing (9626)

This study guide covers topic 11, Video and audio editing, of Cambridge International AS & A Level Information Technology (9626). It follows the Cambridge International AS & A Level Information Technology 9626 syllabus for examination in 2025, 2026 and 2027 (version 3), sections 11.1 Video editing and 11.2 Audio editing. Topic 11 is an AS Level topic, so it is part of both the AS Level and the full A Level. The syllabus bases Paper 1 (Theory) questions on sections 1–11 and Paper 2 (Practical) tasks on sections 8–11, so you can meet this topic in both papers.

The syllabus names no software, so skills are described in general terms. Course hub: Cambridge A Level ICT. Printable checklist: 9626 checklist. Find your gaps with a free 10-minute diagnostic.

What this topic covers

Section	What you must be able to do	Stage
11.1	Edit a video clip to suit its application and audience (structure, text, effects, still images, audio, speed, export, compression)	AS
11.1	Explain the effects of different compression methods on video quality	AS
11.1	Explain why typical video editing features are used	AS
11.1	Give advantages and disadvantages of video export formats	AS
11.2	Edit an audio clip to suit its application and audience (tracks, cleaning, effects, filters, overdubbing, sample rates, export)	AS
11.2	Explain how and why typical audio editing features are used	AS
11.2	Give advantages and disadvantages of audio export formats	AS
11.2	Explain why file size depends on sampling rate and sampling resolution	AS
11.2	Explain the effects of compression on audio quality, files v containers, lossy and lossless	AS

Every edit is judged against one test: does it suit the intended application and audience? A social media advert and a DVD of a school concert need different lengths, formats and file sizes.

11.1 Video editing

Structure: aspect ratio, trimming and splicing

Aspect ratio is the ratio of frame width to height. 16:9 is widescreen; 4:3 is an older, squarer shape; 9:16 is a tall frame for phones held upright. Set it first so everything fits the frame without stretching.

Trimming removes unwanted footage from the start or end of a clip. Cropping removes unwanted edges of the frame. Splicing joins clips end to end on the timeline to build one sequence.

Worked example 1 – trimming. A clip runs from 0:00 to 1:20. The useful part runs from 0:12 to 1:05. Set the new in point at 0:12 and the out point at 1:05.

Kept length = 1:05 − 0:12 = 65 s − 12 s = 53 s

Text on screen

• Titles introduce the video or a section. Text-based slides are full frames of text, such as a title card or instructions.
• Subtitles show the spoken words, for viewing without sound or in another language.
• Captions describe the audio as well as speech (for example “[door slams]”), so a deaf viewer gets the full content.
• Credits acknowledge the people involved and the source of every item you did not create (music, footage, images), respecting copyright and licence terms.
• Scrolling credits move up the screen. Put blank lines between groups (cast, crew, music, image sources) so each group reads separately, and leave blank lines before the first and after the last entry so the text enters and leaves the frame cleanly.

Ensuring readability: use a large, plain font; strong contrast with the background (or an outline or shadow); few words per screen; and enough time on screen to be read.

Effects and transitions

• Fading – fade in from black and out to black, so the video starts and ends smoothly.
• Pan and zoom – moving across or into a frame; on a still image it adds movement and draws attention to a detail.
• Transitions – effects between two clips (cross-dissolve, wipe) that show a change of scene or time. Too many distract.
• Filters and colour correction – adjust brightness, contrast and colour balance so clips shot in different light match, or apply a style such as black and white.

Still images

You may extract a still image (one frame saved as an image) or insert a still image such as a logo or photograph. If its aspect ratio differs from the video’s, crop it to the right shape, then resize it. Scaling width and height by different factors stretches it.

Worked example 2 – matching a 16:9 video. A photograph is 1200 × 900 pixels (4:3). The video is 1920 × 1080 (16:9).

Keep the width 1200. Height for 16:9 = 1200 × 9 ÷ 16 = 675
Crop to 1200 × 675 (remove 225 rows, e.g. some from top and bottom)
Scale factor = 1920 ÷ 1200 = 1.6
1200 × 1.6 = 1920 and 675 × 1.6 = 1080, so resize to 1920 × 1080

Same factor both ways, so no distortion.

Audio in a video

• Adding audio – background music or narration on its own track.
• Editing audio within a clip – change volume, fade music, lower music under speech.
• Removing audio – delete the original sound when it is wind noise or irrelevant chatter.

Speed

Altering the speed changes the playing time: faster fits a long process into a short slot; slower shows detail.

Worked example 3. A 48 s clip is played at 150% speed.

New length = 48 ÷ 1.5 = 32 s

Export and compression

Exporting renders the timeline into one file in a chosen format and resolution.

Format	Advantages	Disadvantages
MP4	Small files for good quality; plays on most computers, phones and websites; suits online sharing	Usually lossy, so some quality is lost
AVI	Long-established Microsoft container; widely played on Windows	Files often large; less suited to web and mobile
MOV	Apple’s QuickTime format; high quality; suits editing work	Files can be large; best supported by Apple software
WMV	Microsoft format; small files	Less well supported on non-Windows devices

Compressing to different resolutions suits the medium:

• DVD – standard-definition resolution in a format DVD players accept.
• Internet – a resolution and bit rate that stream smoothly on typical connections.
• Mobile devices – smaller resolution and file size, saving storage and data.

How compression methods affect video quality

• Lossless compression keeps every pixel exactly: no quality loss, but larger files.
• Lossy compression permanently removes detail the eye is less likely to notice. Files become much smaller. The more aggressive the setting, the more visible the artefacts: blockiness, blurring and banding in smooth colour areas, especially in fast motion.
• Lowering the resolution reduces pixels per frame: smaller files, less sharp on a big screen.
• Lowering the frame rate stores fewer frames each second: smaller files, jerkier motion.
• Lowering the bit rate gives the encoder fewer bits per second: smaller files, more artefacts.
• Intraframe compression compresses each frame on its own; interframe compression stores whole frames at intervals and only the changes between them: much smaller files, but quality drops when much of the picture changes at once.

Why the features are used – summary

Feature	Why it is used
Trimming and cropping	Remove unwanted footage or edges; shorter, more focused video
Text-based slides	Introduce the video or sections; give instructions or key facts
Credits	Acknowledge contributors and sources; meet copyright and licence terms
Captions and subtitles	Accessibility for deaf and hard-of-hearing viewers; viewing without sound; translation
Fading	Smooth, professional start and end; mark a change of section
Extracting a still	Thumbnail, poster or freeze on a key moment
Inserting a still	Show a logo, diagram or photograph not in the footage
Editing audio	Clear speech, balanced music
Exporting in formats	Play on the target device or platform; meet a required format
Compressing to resolutions	Fit the storage, bandwidth and screen of the medium

11.2 Audio editing

Building and cleaning a clip

• Importing new tracks brings recordings in; adding a track to an existing clip layers sound, such as music under speech.
• Trimming removes silence or false starts; splicing joins two clips.
• Fading in and out – volume rises from or falls to silence, avoiding sudden starts.
• Normalising applies the same gain to the whole clip so its loudest peak reaches a target level. Clips recorded at different levels then play at a consistent volume, with the balance within each clip unchanged.
• DC offset is when the waveform is shifted so it is not centred on the zero line. It wastes headroom and can cause clicks at edits. Remove it before normalising so the waveform is centred.
• Noise reduction removes steady background noise (hum, hiss). Typically you select a noise-only section for the software to learn, then reduce it across the clip. Too much makes speech sound thin.

Changing the sound

• Clip speed – faster or slower playback, changing duration.
• Pitch – higher or lower notes or voice, for effect or to disguise a voice.
• Delay/echo – distinct repeats of the sound after a set time, each quieter.
• Reverberation – many dense reflections blended together, so it sounds as if recorded in a hall or room.
• Stereo to mono – combines two channels into one; uncompressed, the file halves. Suits speech.
• Equalisation (EQ) – boosts or cuts chosen frequency bands, for example to make speech clearer.
• High pass filter – lets frequencies above a cut-off through and removes lower ones such as rumble and hum.
• Low pass filter – lets frequencies below a cut-off through and removes higher ones such as hiss.
• Overdubbing – recording new audio over or alongside existing audio. A voiceover is narration overdubbed on music or video.

Sampling, file size and sample rates

Sampling rate is the number of samples of the sound wave taken per second (hertz). Sampling resolution (bit depth) is the number of bits stored per sample. A higher rate follows the wave’s shape more closely; a higher resolution records each amplitude more precisely. Both improve quality and increase file size.

Uncompressed size (bits) = sampling rate × sampling resolution × channels × seconds

Worked example 4. 30 s of stereo audio at 40,000 Hz, 16 bits (take 1 MB = 1,000,000 bytes).

40,000 × 16 × 2 × 30 = 38,400,000 bits
38,400,000 ÷ 8 = 4,800,000 bytes = 4.8 MB
Mono: 2.4 MB.  Mono at 20,000 Hz: 1.2 MB

Compressing to different sample rates suits the medium: high rates for music and master copies, lower rates for speech or web clips where small files matter more.

Export formats

Format	Advantages	Disadvantages
MP3	Lossy: small files; plays almost everywhere	Quality lost, worst at low bit rates; poor for further editing
MP4a	MPEG-4 audio file (often .m4a); usually holds AAC, so good quality for size	Not supported by every older player
WAV	Usually uncompressed: full quality; ideal for editing and master copies	Very large files
AAC	Lossy, but generally better quality than MP3 at the same bit rate	Slightly less universal than MP3

Compression, files and containers

• Lossless compression shrinks the file but the original can be rebuilt exactly, so quality is unchanged. Files are larger than lossy ones.
• Lossy compression removes sounds people are least likely to notice. Files are much smaller; low bit rates sound dull or “swishy”, and lost quality cannot be recovered.
• Files v containers: a plain audio file (such as MP3) holds one stream encoded one way. A container (such as MP4) is a wrapper that can hold one or more streams – audio, video, subtitles – plus information about them. The codec inside decides the compression, so two files with the same container extension can differ in quality and size.

Common errors

• Resizing an image to the video’s dimensions without cropping, so it is stretched.
• Calling a caption a subtitle: captions also describe non-speech sound.
• Saying normalising “removes noise”. It changes volume only; noise reduction removes noise.
• Forgetting to divide by 8, or mixing up stereo (×2) and mono.
• Giving an export format with no reason linked to the device, audience or file size.

Next steps

Condense this with the Video and audio editing revision notes, then test yourself on the Video and audio editing practice questions. Compression as a utility is in Hardware and Software.

Official syllabus

Cambridge International AS & A Level Information Technology 9626, syllabus for examination in 2025, 2026 and 2027, version 3, Cambridge University Press & Assessment. Topic 11: Video and audio editing (11.1 Video editing; 11.2 Audio editing).