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Audiovisual digital documents

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  1. Audiovisual digital documents Adolf Knoll National Library of the Czech Republic adolf.knoll@nkp.cz

  2. New digital audio recordings New digital video recordings Digitized analogue audio recordings Digitized movies Reformatted digital documents for better computer use Digitally born vs. digitized

  3. Compressed vs. uncompressed • Only sound recordings can be stored in uncompressed digital form / WAVE or CDA formats • Video is always compressed

  4. Compressed audio and video • MPEG initiatives / it provides compression solutions for both • MPEG • Intra-frame coding technique • Extra-frame coding technique

  5. Intra-Frame Coding

  6. Non-Intra Frame Coding

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

  8. 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 quality MP3 comes from here

  9. 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

  10. 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.

  11. 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

  12. MPEG-2 Advanced Audio Coding • AAC – another perceptual coding scheme • Better prediction algorithm • 5 channels as in cinema today C L R L – left R – right C – centre LS – left-surround RS – right-surround Used for DVD RS LS

  13. 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

  14. 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)

  15. MPEG-4 Added e.g bitrate scalability and object-based representation

  16. 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)

  17. 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

  18. 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

  19. To compare… VCD vs. DIVx vs. SVCD All of them compressed to store a movie (1 hr 30 mins) on 2 CDs

  20. 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