Transcript Audiovisual digital documents

Audiovisual digital documents
Adolf Knoll
National Library of the Czech
Republic
[email protected]
Digitally born vs. digitized
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New digital audio
recordings
New digital video
recordings
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Digitized analogue
audio recordings
Digitized movies
Reformatted digital
documents for
better computer
use
Compressed vs.
uncompressed
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Only sound recordings can be stored
in uncompressed digital form / WAVE
or CDA formats
Video is always compressed
Compressed audio and video
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MPEG initiatives / it provides
compression solutions for both
MPEG
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Intra-frame coding technique
Extra-frame coding technique
Intra-Frame Coding
Non-Intra Frame Coding
How it works…
I – Intra-Frame
P – Predicted Future Frame
B - Bi-directional interpolated prediction frames
MPEG-1 for audio
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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)
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1:6…1:8 (layer two)
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1:10…1:12 (layer three) – 128…112 kbps
… to preserve CD quality
MP3 comes from here
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MP3 – typical performances
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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
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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
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MPEG-2 was finalized in 1994 for digital television
broadcasting, such as the efficient coding of fieldinterlaced video.
720x480 resolution video at 30 frames/sec, at bitrates 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
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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
LS
RS
Used for DVD
Encoding CD audio
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Both MP3 and AAC can maintain nearCD 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
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Similar acoustic impression at 64 kbps as
MP3 at 128 kbps
MP3pro
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3 parts of signal:
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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 objectbased representation
Media
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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
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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
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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
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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