Audiovisual digital documents Adolf Knoll National Library of the Czech Republic

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-Frame P – Predicted Future Frame B - Bi-directional interpolated prediction frames How it works…

MPEG-1 for audio Started in 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 quality MP3 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 LR C RS LS L – left R – right C – centre LS – left-surround RS – 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:  kHz (usual MP3 coder) – it is seen by ordinary players  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 ( kHz) and raised up by a pitch up to 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; 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); 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