Audio and Video Processing and Post-Production
What this domain tests
The signal-processing decisions inside an editing suite: audio dynamics and loudness, colour management, keying and compositing, and delivery encoding. Items ask why a step is performed or what a delivery parameter implies.
Core rules and concepts
- Audio. Sample-rate and bit-depth conversion require dither when reducing depth to avoid correlated distortion. Normalisation scales peak level; compression reduces dynamic range above a threshold; limiting prevents clipping; a noise gate attenuates below a threshold; EQ shapes frequency balance; reverb adds synthetic space; denoising must be applied cautiously. Broadcast loudness targets use ITU-R BS.1770 LUFS rather than peak meters, because peaks do not describe perceived loudness.
- Video. Non-linear editing workflow: ingest/import, three-point editing, insert versus overwrite edits, ripple and roll, J and L cuts for split audio, transitions, keyframed effects, titles.
- Colour. Primary correction fixes the whole image (exposure, white balance); secondary correction targets a hue or region. LUTs apply defined transforms. Use waveform and vectorscope rather than the eye. Know the working colour space (Rec.709 for HD, Rec.2020 for UHD) and handle log footage with an appropriate transform.
- Compositing. Chroma key (green for subject separation from skin and hair, blue where green clothing is present), rotoscoping, motion tracking, blend modes, and premultiplied alpha handling.
- Delivery. Distinguish container from codec: MP4 is a container that may hold H.264 video and AAC audio. Rate control is CBR, VBR or constant-quality (CRF); VBR gives better quality per bit for on-demand content.
Worked example
A 60-second 1080p25 clip encoded at 8 Mbit/s: 60 s × 8 Mbit/s = 480 Mbit = 60 MB. If the client demands the file fit a 25 MB upload limit, required bit rate ≈ 25 MB × 8 / 60 s ≈ 3.3 Mbit/s, so you must cut the rate roughly by 60%, or shorten the clip, or reduce resolution. Showing the arithmetic plus the trade-off is the expected answer.
Traps that cost marks
- Mixing up container and codec in delivery specifications.
- Confusing normalisation (peak scaling) with compression (dynamic-range reduction).
- Judging colour by monitor appearance rather than scopes.
- Assuming CBR is always safer; it wastes bits on simple scenes.