Digital Audiovisual Properties - Basics

Peter Bubestinger-Steindl
(peter @ ArkThis.com)

October 2022

Overview

Video Audio
  • Image resolution
  • Framerate (fps)
  • Audio: Samplerate
  • Audio: Bit-depth
  • Audio: Channels

Image Resolution

  • = Width * Height
  • In Pixel (px)

Important Resolutions

Pixel (px) Norm
720 x 486 NTSC SD
720 x 576 PAL SD
1280 x 720 HD-Ready
1920 x 1080 Full-HD
2048 x 1080 2K (Digital Cinema)
4096 x 2160 4K (Digital Cinema)

 

See also: Image Resolution (Wikipedia) and Display Resolution (Wikipedia)

Per Video Format

Pixel (px) Norm
500 x 480 Digital8
720 x 480 NTSC (DVD, miniDV, DigiBeta)
720 x 576 PAL DVD, miniDV, Digital8, DigiBeta
1280 x 720 HD DVD, Blu-ray, HDV
1440 x 1080 HDV (anamorph)
1920 x 1080 HDV, AVCHD, HD DVD, Blu-ray, HDCAM SR
3840 x 2160 UHD-1

Video Resolutions

Video resolution standards

Framerate

Framerate

  • Images (=Frames) Per Second (FPS)

Framerates

Norm Framerate
PAL / SECAM 25 fps
NTSC ca. 29.97 fps (= 30000/1001)
Film 24 fps
Film (NTSC) ca. 23.98 fps (= 24000/1001)

Europe: 50 Hz fps = AC frequency / 2 America 60 Hz

Thanks AEG for 50Hz! 😉️

CFR: Constant Framerate

Each frame has a fixed (=constant) duration.

VFR: Variable Framerate

Each frame has an arbitrary (=variable) duration.

MediaInfo Report of VFR

Variable Framerate

  • No constant image frequency.
  • Each frame has individual display duration.
  • Was rather uncommon.
  • But came back increasingly with smartphone/tablet recordings.
  • Mixing CFR and VFR: “Something’s gotta give”
  • May produce “unusual” frame rates when checking (because average).

Audio

  • Samplerate
  • Bits per sample (bit depth)
  • Channels

Samplerate

Hertz? kHz?

Samplerate is given as frequency:
1 kHz (Kilohertz) = 1000 Hz (Hertz)

Each audio sample is literally just a number. Representing the audio volume (voltage) at that position.

Example Audio CD:
44.1 kHz = 44100 samples per second

Bits per Sample

More Bits = More Precision = More Space

Bits Range
4 0..15
8 0..255
16 0..65535
24 0..16777216 16.7 Mio
32 0..4294967296 (a lot!)

filesize (MB) = bits * samplerate * channels * duration / 8 / 1024 / 1024

PCM, aka “Uncompressed”

  • Pulse Code Modulation
  • Linear PCM: Most native form of digital audio
  • Popular container(if audio-only) = WAV

Common Samplerate & Bits

Rate (Hz) Bits Application
11025 8
44100 16
48000 24
96000 32

Audio Channels

  • 1 = mono
  • 2 = left + right (stereo, dual-mono)
  • > 2 = multi-channel
  • …

Preserve, and/or document the source track/channel layout.

Audio: Tracks & Channels

  • Each AV file can have multiple tracks
  • Each track can have n channels
  • Common: 1 stereo (=2 channels) track per language
  • Broadcast: 8 individual tracks, 1 channel each.
  • …

Audio channel mapping is another story…

Samplerate: How much?

“Sufficient” samplerate = 2*max(f) (at least) twice the highest frequency of to-be-sampled content.

(See Nyquist–Shannon sampling theorem)

Questions?

Comments?

More to know about digital AV: