Transcript Audiovisual digital documents

Unit no. 3
Digitizing Sound and Video
Adolf Knoll
National Library of the Czech Republic
[email protected]
Learning objectives
After the completion of this unit the learner
will be able to:
 Understand the digital sound and the
digital video
 Apply basic solutions both for normal use
and archiving
 Digitize correctly sound and video and
make the most common products (VCD,
SVCD, DVD Video, etc.)
Digitization of analogue audio and
video
 The analogue data in audio and video domains
are most often stored on these carriers:
 Magnetic tapes, be they in reels, audio cassettes,
VHS, Video 8, and others
 Black shellac and vinyl discs
 These media can be replayed only on
appropriate replay devices (gramophone, video
cassette recorder/player, video cameras, etc.)
How to digitize them?
 The replay device must be connected to a
conversion device:
 Sound card in the computer for audio (Line-In
Connector)
 TV card or video chip that enables the conversion of
the analogue video into the digital one (built-in or USB
connected to a computer, available in a digital video
recorder or camera, …)
 For data capture the software or utility must be
used that enable it
Line-In connector
of the sound card
Analogue signal
from the headphones
connector
Digitization of a vinyl disc
Video 8 analogue
camera
USB converter
Digitization of a Video 8
analogue recording
Audiovisual formats: MPEG
 Motion Pictures Expert Group (MPEG) has
developed several standards from which
some are highly used:
 MPEG-1 (1988) – typical application:
VideoCD (VCD)
 MPEG-2 (1994) – typical application: DVD
video or Digital TV
 MPEG-4 – typical application: DivX or Xvid
movies
Sound in MPEG
 The sound in an MPEG video can be stored in 3
possible layers. The layer no. 3 is known
separately as MP3 audio format
 Other digital audio formats are: WAVE, WMA,
OGG, MP3pro, AAC, …
 The sound in the audio CD is uncompressed,
while in the computer world the uncompressed
sound – especially for archiving – is stored in the
WAVE format (*.wav)
 Most standalone players can also play MP3
audio, while some of them can play also the
WMA or even AAC files
Bitrate in audio files
 bitrate in kbit/s
 audio CD: 1411 kbit/s
 MP3 CD quality: min. 128 kbit/s
 Lower bitrate possible when our
requirements are not so high and/or when
we may use WMA, AAC, or other formats
 as the space needed for storage of digital
audio is not critical today, we should avoid
lower bitrates
MPEG-1 in VideoCD
 VCD is playable on standalone players
 VCD legal settings:
 bitrate: 1140 kbit/s
 sound: 224 kbit/s in MPEG-1 layer 2
 still image resolution: 352x288 pixels in PAL, 352x240
in NTSC
 25 frames/s in PAL, 23.976 frames/s in NTSC
VideoCD is a product that has a firm structure.
 One CD can contain ca. 70 minutes of VHS-like
video quality
MPEG-2 in DVD video
 DVD video that is playable on standalone
players
 Video DVD most typical legal settings:
 bitrate: variable from 2.4 up to 9.6 mbit/s
 sound: 192 kbit/s and more in MPEG layer 2 or PCM
(uncompressed), AAC
 still image resolution: 720x576 pixels in PAL
 25 frames/s in PAL
 DVD video is a product that has a firm structure,
it consists if video objects (VOB). One DVD can
contain from ca. 60 minutes (high quality) to
several hours of video (lower quality)
MPEG-2 in SuperVideoCD
 SVCD is playable on standalone players
 SVCD legal settings:
 bitrate: max. 2600 kbit/s
 sound: 32 - 384 kbit/s in MPEG layer 2
 still image resolution: 480x576 pixels in PAL, 480x480
NTSC
 25 frames/s in PAL, 29,97 frames/s in NTSC
 SVCD is a product that has a firm structure. One
SVCD can contain ca. 35 or more minutes of
video
VCD – MPEG1
Comparison of image resolution in typical optical disc video products
SVCD – MPEG2
DVD – MPEG2
MPEG-4
 Lower variable bitrate with comparably same quality as
in MPEG-2 (approx. 780 kbit/s gives good results)
 Can be combined with sound in various formats, but
most typically MP3
 Used mostly as DivX or Xvid approaches to encode
MPEG-4, but possible also other ones, as e.g.
NeroDigital
 The video and audio parameters can be various, but
some profiles are used the coimpatibility with standalone
devices, e.g. the Theatre Profile ensures the videos can
be replayed on standalone DVD players (most of them
can play also MPEG-4)
MPEG in computers
 *.mpg/mpeg – it does not say whether it is
MPEG 1 or 2
 MPEG-4 is usually packed in *.avi; if it is made
as NeroDigital then packed as *.mp4
 AVI format (Audio-Video Interleave) can contain
a large variety of video and audio formats (it
must be always set up appropriately) or it can be
uncompressed (very large files)
 From other formats, most used is the Microsoft
WMA
What to use: software
 Audiograbber (freeware at http://www.audiograbber.com



us.net): it enables the Line-In recording of analogue
sound
Video converters come usually with basic software, most
typically they convert into MPEG-2
DVD authoring: the low cost NERO Premium
(http://www.nero.com) is a good solution
For MPEG-4, the Xvid (http://www.xvid.org) authoring is
based on freeware, while the for DivX
(http://www.divx.com) encoding, the encoder must be
purchased
For work with Xvid (but not only), you may use the free
Auto Gordian Knot software (http://www.autogk.me.uk)
What to use: formats and
parameters
 For audio use *.wav whenever possible and MP3 with
rich bitrates for applications
 For video convert into MPEG-2 with at least 4 mbit/s
variable bitrate (mostly enough for current VHS or
Video8 quality) and 224 kbit/s MPEG Layer 2 sound
 Make all the other formats and/or products afterwards
(e.g. WMA or AVI Xvid video clips for Internet or VCD,
SVCD, or DVD Video) from this master file that you
should preserve
 Mind that for replay of special parameters you must have
special codecs (installed pieces of software that
decode/encode the files); therefore, avoid very special
untypical settings
Further information
 MPEG website:
http://www.chiariglione.org/mpeg
 Further information for those who are
about to start: http://www.videohelp.com/