Digital Audiovisual Properties
Advanced

Peter Bubestinger-Steindl
(p.bubestinger@av-rd.com)

March 2019

Audio vs. Video

Aspect Ratio

Most people only mean/know the "Display Aspect Ratio" (DAR).

  • 4:3
  • 16:9
  • 5:4

DAR... SAR? PAR!

  • DAR: Display Aspect Ratio
  • SAR: Storage Aspect Ratio
  • PAR: Pixel Aspect Ratio

Formula: DAR = SAR x PAR

Letterbox

Pillarbox

Windowbox

Anamorphic Video

Format DAR SAR Resolution
Digibeta 16:9 5:4 720 x 576
HDV 16:9 4:3 1440 x 1080

Good to know

DVD SAR = 5:4
So 16:9 is either letterboxed or anamorphic.

HD is always DAR=16:9
4:3 in HD is impossible without editing.

Interlacing

  • 2 fields in one frame
  • Field: half of vertical resolution
  • Field: twice the time resolution

Top Field

Bottom Field

GOP: Group Of Pictures

The GOP is a group of pictures in a video that are depending on each other.

GOP Frametypes

  • [I]ntra:
    Independently encoded single frame (aka "keyframe")
  • [P]redictive-coded:
    Difference-informations to previous I- or P-Frame.
  • [B]idirectional predictive-coded:
    Difference-informations to previous and/or subsequent I- or P-Frame.

GOP and Recording

  • Recording should be done with GOP=1.
  • This means:
    only I-Frames (=no dependencies between frames).

GOP and Editing

  • With GOP = 1: No issues.
  • With GOP > 1: Watch out!

btw: Some programs are able to perform "GOP-aware" cuts

Color models

  • RGB (Red-Green-Blue)
  • YUV (Luma/Chroma)

Note: Those are just 2 for video. There are more...

Color Model: RGB

Color Model: YUV

Bits Per Component/Sample

Color Components

  • RGB: Red, Green, Blue
  • YUV: Y', Cb, Cr

Bits Per Component/Sample

BPC Gray shades Pixel Byte(s)
8 2^8 = [0..255] 24 Bits 3 Bytes
10 2^10 = [0..1023] 30 Bits 6|4 Bytes
16 2^16 = [0..65535] 48 Bits 6 Bytes

Chroma Subsampling

The color information in YUV is stored in a reduced resolution.

This principle originates from analog transmission and was kept in digital, because it allows smaller data sizes.

"J:a:b" Notation

J: Horiz. sampling reference (usually "4").
a: Number of color samples in 1st row of J pixels.
b: Number of change in color samples between 1st / 2nd row of J pixels.

Chroma Subsampling

Confusion / FUD?

Diskspace

BPC Subsampling Speicherplatz
8 4:2:2 1.16 / 1.74 GB
10 4:2:2 1.45 / 2.17 GB
16 4:2:2 2.32 / 3.48 GB

Questions?

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