Audiovisual digital documents

Adolf KnollNational Library of the Czech Republicadolf.knoll@nkp.cz

Digitally born vs. digitized

New digital audio recordings

New digital video recordings

Digitized analogue audio recordings

Digitized movies

Reformatted digital documents for better computer use

Compressed vs. uncompressed

Only sound recordings can be stored in uncompressed digital form / WAVE or CDA formats

Video is always compressed

Compressed audio and video

MPEG initiatives / it provides compression solutions for both

MPEG Intra-frame coding technique Extra-frame coding technique

Intra-Frame Coding

Non-Intra Frame Coding

I – Intra-FrameP – Predicted Future FrameB - Bi-directional interpolated prediction frames

How it works…

MPEG-1 for audio

Started in 1988 3 operating modes/layers Without data reduction more than 1400 kbps for 1

second of stereo signal = 175 KB, i.e. 1 hr = 630 MB

Compression ratios 1:4 (layer one) 1:6…1:8 (layer two) 1:10…1:12 (layer three) – 128…112 kbps… to preserve CD qualityMP3 comes from here

MP3 – typical performances

Telephone sound…. 8 kbps (96:1) Better short-wave radio…. 16 kbps

(48:1) FM radio…. 56…64 kbps (16:1) Near-CD…. 96 kbps (16:1 – usually

free in most codecs) CD…. 112…128 kbps

MPEG-1 video

Used until today as the format for the so-called VideoCD

It is comparable to the perception of a VHS analogue recording

Almost all DVD players can play also VideoCD It does not use complex encoding methods MPEG-1 was finalized in 1991, and was originally

optimized to work at video resolutions of 352x240 pixels at 30 frames/sec (NTSC based) or 352x288 pixels at 25 frames/sec (PAL based), commonly referred to as Source Input Format (SIF) video.

MPEG-2

MPEG-2 was finalized in 1994 for digital television broadcasting, such as the efficient coding of field-interlaced video.

720x480 resolution video at 30 frames/sec, at bit-rates up to 15 Mb/sec for NTSC video

HDTV resolution of 1920x1080 pixels at 30 frame/sec, at a bit-rate of up to 80 Mb/sec

Used for DVD movies Used also for SuperVideoCD (SVCD) media that

can be played in some DVD players (not all of them) – but here with lower resolution

MPEG-2 Advanced Audio Coding

AAC – another perceptual coding scheme Better prediction algorithm 5 channels as in cinema today

L R

C

RSLS

L – leftR – rightC – centreLS – left-surroundRS – right-surround

Used for DVD

Encoding CD audio

Both MP3 and AAC can maintain near-CD quality – AAC 50% more data for the same media, i.e. it can do at 96 kbps what MP3 does at 128 kbps

Other formats: WMA and MP3pro Similar acoustic impression at 64 kbps as

MP3 at 128 kbps

MP3pro

3 parts of signal: 0-8.1 kHz (usual MP3 coder) – it is seen by ordinary

players 8.2-16.3 kHz (calculating average power per frame) more than 16.3 kHz (deleted)

When decoding the middle part is selected the middle frequency part of it (4.1-8.1 kHz) and raised up by a pitch up to 8.2-16.3 kHz

Good for average players and music with less high tones (no high bitrate support, synthese of high frequences from low ones)

MPEG-4

Added e.g bitrate scalability and object-based representation

Media

DVD - commercial: MPEG2 with AAC; 3 – 8 mbps; 720x480 in PAL; 30-70 MB/min (15-20 min per CD)

VCD – MPEG-1; 1.15 mbps; 352x288 in PAL; 10 MB/min (74 min per CD)

SVCD – MPEG-2; variable up to 2.6 mbps; 480x576 in PAL (MPEG-1, layer II); 10-20 MB/min (35-60 min per CD)

Other possibilities

DivX or xvid codecs MPEG-4 in very high quality and usually

MP3 for sound (but also other sound format) – stored in AVI container

High resolution and high quality DVD back-up – usually 2 CDs per one movie

Can be used for making VCD or SVCD

How to backup a DVD

Rip the files onto hard disk Calculate the desirable bitrate keeping

in view the size of media for storage Encode Cut if necessary into parts for storage

on more media units Free software tools available for this

To compare…

VCD vs. DIVx vs. SVCD

All of them compressed to store a movie (1 hr 30 mins)on 2 CDs

Usage of audio and video on the web

For creating better research environment

Taking care of legal approach Video sequences or audio files in

higher compression can be referenced from web pages, downloaded/streamed, and enjoyed