Digital Video on PC’sDigital Video on PC’s

What advantage does having What advantage does having video on PCs in digital form video on PCs in digital form have over the various other have over the various other

formats?formats?

Digital Video - Digital Video - AdvantagesAdvantages

Can be used with very little extra hardwareCan be used with very little extra hardware– just larger hard disksjust larger hard disks– video from tape video from tape cancan be shown on the PC be shown on the PC

monitor but quality interface cards to do this monitor but quality interface cards to do this are costly - plus cost of video equipmentare costly - plus cost of video equipment

Almost random accessAlmost random access– videotape is sequentialvideotape is sequential

slow to editslow to edit

impractical for interactive applicationsimpractical for interactive applications

Digital Video – Digital Video – Advantages contAdvantages cont

Quality Editing and DuplicationQuality Editing and Duplication– copies are exact - tape copies are imperfectcopies are exact - tape copies are imperfect– frame by frame editingframe by frame editing– only degradation of edited material is due to only degradation of edited material is due to

lossy compressionlossy compression

Storage FlexibilityStorage Flexibility– long life – Hard disk 30,000 hrs - professional long life – Hard disk 30,000 hrs - professional

tape 3 hrstape 3 hrs

Ease of useEase of use

Digital Video Digital Video DisadvantagesDisadvantages

Requires lots of storage spaceRequires lots of storage space

PC performance is constrainedPC performance is constrained

– getting the images from disk to screen quickly getting the images from disk to screen quickly enough to avoid jerky motionenough to avoid jerky motion

Large image size only practical on powerful machinesLarge image size only practical on powerful machines

– 240 240 180 not uncommon180 not uncommon

– 320 320 240 practical240 practical

– 640 640 480 with hardware support480 with hardware supportAchievable frame rates go down as image size goes Achievable frame rates go down as image size goes

upup

Common Digital Common Digital Video TerminologyVideo Terminology

Full frame: 640 x 480Full frame: 640 x 480Half frame: 320 x 240Half frame: 320 x 240

– MPEG 1MPEG 1– is actually one-quarter screenis actually one-quarter screen

Quarter frame: 160 x 120 Quarter frame: 160 x 120 – Streaming/webcam “postage stamp”Streaming/webcam “postage stamp”– is actually one-sixteenth screenis actually one-sixteenth screen

Full motion:Full motion:– 30 fps (NTSC)30 fps (NTSC)– 25 fps (PAL)25 fps (PAL)

Full colour: 24-bits - 16 million coloursFull colour: 24-bits - 16 million colours

Standard Digital Video Standard Digital Video Resolution TerminologyResolution Terminology

MPEG termsMPEG terms– SIF Standard Image Format SIF Standard Image Format

H.261 (ITU-R) video conferencing termsH.261 (ITU-R) video conferencing terms– CIF Common Intermediate Format CIF Common Intermediate Format – QCIF Quarter Common Intermediate Format QCIF Quarter Common Intermediate Format

Square pixel Square pixel formatsformats

Square pixels PAL:Square pixels PAL:– full-screen - 768 x 576full-screen - 768 x 576

– SIF – 352 x 288SIF – 352 x 288

– CIF - 384 x 288 – quarter screenCIF - 384 x 288 – quarter screen

– QCIF - 192 x 144QCIF - 192 x 144

– sub QCIF - 128 x 96sub QCIF - 128 x 96

Square pixels NTSC:Square pixels NTSC:– full-screen - 640 x 480 full-screen - 640 x 480

– CIF - 352 x 240– quarter screenCIF - 352 x 240– quarter screen

– QCIF - 176 x 120QCIF - 176 x 120

– sub QCIF - 118 x 80sub QCIF - 118 x 80

CCIR pixel CCIR pixel formatsformats

CCIR 601 pixels PAL:CCIR 601 pixels PAL:– full-screen - 720 x 576full-screen - 720 x 576– SIF – 360 x 288SIF – 360 x 288– CIF - 360 x 288– quarter screenCIF - 360 x 288– quarter screen– QCIF - 180 x 144QCIF - 180 x 144– sub QCIF - 118 x 96sub QCIF - 118 x 96

CCIR 601 pixels NTSC:CCIR 601 pixels NTSC:– full-screen - 720 x 480 full-screen - 720 x 480 – SIF –360 x 240SIF –360 x 240– CIF - 360 x 240– quarter screenCIF - 360 x 240– quarter screen– QCIF - 180 x 120QCIF - 180 x 120– sub QCIF - 118 x 80sub QCIF - 118 x 80

MPEGMPEG

MPEG-1 for computer screens – 320 x 240MPEG-1 for computer screens – 320 x 240

MPEG-2 also allows for larger formats: 1440 MPEG-2 also allows for larger formats: 1440 x 1152; 1920 x 1080 (16:9)x 1152; 1920 x 1080 (16:9)

Analogue CaptureAnalogue Capture

UK TV images and PC screen sizes do not UK TV images and PC screen sizes do not matchmatch– PAL images are (768) PAL images are (768) 588; NTSC (720) 588; NTSC (720)

480480composite signals composite signals

– professional sampling rates standards give: professional sampling rates standards give: PAL (864) PAL (864) 588; NTSC (858) 588; NTSC (858) 490490

component signalscomponent signals

but several of the lines sampled and parts of each but several of the lines sampled and parts of each line do not form part of the pictureline do not form part of the picture

TV croppingTV cropping

pixels can be cut off the image edges (top, bottom, pixels can be cut off the image edges (top, bottom, left, right). For many applications, these areas are left, right). For many applications, these areas are not visible and removing them saves on the not visible and removing them saves on the amount of data captured with no visible amount of data captured with no visible degradation in qualitydegradation in quality

e.g., Square pixels PAL:e.g., Square pixels PAL:– full-screen - 720 x 540full-screen - 720 x 540– half-screen – 360 x 540half-screen – 360 x 540– CIF - 360 x 270 – quarter screenCIF - 360 x 270 – quarter screen

still different from screen resolutionstill different from screen resolution

TV frame ratesTV frame rates

– NTSC 30 fps, PAL/SECAM 25 fpsNTSC 30 fps, PAL/SECAM 25 fps

are different from:are different from:– arbitrary capture ratesarbitrary capture rates

30 fps OK for capture of US material; not so for UK30 fps OK for capture of US material; not so for UK

– pc screen refresh rates; 72Hz+ Non-pc screen refresh rates; 72Hz+ Non-Interlaced typicallyInterlaced typically

– not usually related in any way to video frame not usually related in any way to video frame ratesrates

Digital Video Digital Video (Camera) Capture(Camera) Capture

Light hits CCDs (charge coupled devices) Light hits CCDs (charge coupled devices) and generates electric currents and generates electric currents

Electronics encodes the electrical signal into Electronics encodes the electrical signal into three parts:three parts:– LuminanceLuminance– Red differenceRed difference– Blue differenceBlue difference

The signals are sampled and quantisedThe signals are sampled and quantised

Digital Video (Camera) Digital Video (Camera) Capture 2Capture 2

The digital information is then compressed The digital information is then compressed in three stages:in three stages:– DCT (Discrete Cosine Transform)DCT (Discrete Cosine Transform)

using 8 x 8 pixel blocksusing 8 x 8 pixel blocks

– AQ (Adaptive Quantisation)AQ (Adaptive Quantisation)reduces complexity of DCT output (if necessary) reduces complexity of DCT output (if necessary) to improve VLE effectiveness - to improve VLE effectiveness - lossylossy

– VLE (Variable Length Encoding)VLE (Variable Length Encoding)

Digital VideoDigital Video

Video – Television Video – Television StandardsStandards

What are the names of the TV standards in: What are the names of the TV standards in: USA, Japan, UK, France, Australia, and USA, Japan, UK, France, Australia, and Russia?Russia?

How do these standards differ?How do these standards differ?

Can one TV receive all the standards?Can one TV receive all the standards?

See See http://en.wikipedia.org/wiki/Broadcast_telehttp://en.wikipedia.org/wiki/Broadcast_television_systemsvision_systems

NTSC – National NTSC – National Television Standards Television Standards

CommitteeCommittee

USA, Canada, Central America, Japan, etc.USA, Canada, Central America, Japan, etc.

525525 line line 6060Hz interlaced – Hz interlaced – 6060 fields/s, fields/s, 3030 frames/secframes/sec– interlacedinterlaced

525525//59.9459.94//2:12:1

uses YIQ model ( a conversion of RGB uses YIQ model ( a conversion of RGB colour)colour)

NTSC 4.43 (NTSC video signal, PAL colour NTSC 4.43 (NTSC video signal, PAL colour carrier) 525/carrier) 525/29.9729.97/2:1/2:1

PAL – Phase PAL – Phase Alternate LineAlternate Line

UK, Western Europe (except France), Australia, UK, Western Europe (except France), Australia, South Africa, India, China, etc.South Africa, India, China, etc.

625625 line line 5050Hz interlaced – Hz interlaced – 5050 fields/s, fields/s, 2525 frames/sframes/s

625625//5050//2:12:1

uses YUV modeluses YUV modelPAL M (e.g. Brazil) 525/29.97/2:1PAL M (e.g. Brazil) 525/29.97/2:1

PAL N (e.g. Argentina) 625/50/2:1PAL N (e.g. Argentina) 625/50/2:1

Note: TV picture does not use all linesNote: TV picture does not use all lines

SECAM – Système SECAM – Système Electronique pour Coleur Electronique pour Coleur

avec Mémoireavec Mémoire

France, Eastern Europe, Russia, parts of France, Eastern Europe, Russia, parts of Africa and the Middle EastAfrica and the Middle East

625 line 50Hz interlaced – 50 fields/s, 25 625 line 50Hz interlaced – 50 fields/s, 25 frames/sframes/s

TV images sizes TV images sizes in pixelsin pixels

In reality these are samples of an analogue In reality these are samples of an analogue signalsignal

PAL images are (768) PAL images are (768) 576; NTSC (720) 576; NTSC (720) 480480

actually: PAL (864) actually: PAL (864) 625; NTSC (858) 625; NTSC (858) 525525– but several of the lines sampled and parts of but several of the lines sampled and parts of

each line do not form part of the pictureeach line do not form part of the picture

Aspect RatioAspect Ratio

Aspect Ratio – horizontal to vertical, Aspect Ratio – horizontal to vertical, nominally, 4:3 on TV defines the ratios 768 nominally, 4:3 on TV defines the ratios 768 576 & 720 576 & 720 480480

so video capture of analogue signals is so video capture of analogue signals is normally done at (maximum) these figures: normally done at (maximum) these figures: 768 768 576 & 720 576 & 720 480480

16:9 on HDTV (1920 16:9 on HDTV (1920 1080)and on 1080)and on widescreenwidescreen

Note: Film runs at Note: Film runs at 24fps24fps

when played on 50Hz TV (telecine) it runs at when played on 50Hz TV (telecine) it runs at 25fps i.e. 50 fields/s25fps i.e. 50 fields/s

Movies run a little faster on TV!Movies run a little faster on TV!

when played on 60Hz TV in order to get 60 when played on 60Hz TV in order to get 60 fields/s the second field of every other fields/s the second field of every other frame is broadcast twice ‘frame is broadcast twice ‘3-2 pulldown3-2 pulldown’’– i.e. the first frame of the film is recorded for i.e. the first frame of the film is recorded for

three fields, the second for two, the third for three fields, the second for two, the third for three, and so on ...three, and so on ...

Video Tape Video Tape FormatsFormats

What are the names of the main video tape What are the names of the main video tape formats?formats?

How do they differ?How do they differ?

If you have a video tape from the US in your If you have a video tape from the US in your video player’s tape format can you be sure video player’s tape format can you be sure it will play OK?it will play OK?

Analogue Tape Analogue Tape FormatsFormats

VHS (Video Home System - 1976) - ½” tape VHS (Video Home System - 1976) - ½” tape andand Video8 - 8mm tape Video8 - 8mm tape– suitable for normal TV recordingsuitable for normal TV recording– 1 helical track for video (composite) 1 straight 1 helical track for video (composite) 1 straight

track for sound; (track for sound; (C chroma)C chroma)– resolve 240 and 230 linesresolve 240 and 230 lines

Betamax - ½” Betamax - ½” tapetape

suitable for normal TV recordingsuitable for normal TV recording

composite but superior to VHScomposite but superior to VHS

almost obsoletealmost obsolete

Super VHS (S-VHS) - ½” Super VHS (S-VHS) - ½” tape tape

& High-Band 8mm (Hi-8)& High-Band 8mm (Hi-8)

superior to VHSsuperior to VHS

Y/C component using Y/C component using S-VideoS-Video connections connections to keep the signals separateto keep the signals separate

suitable for in-house semi-pro worksuitable for in-house semi-pro work

resolve 400 linesresolve 400 lines

S-VideoS-Video is is notnot a tape a tape format: Separate Videoformat: Separate Video

Betacam SP (Sony) - ½” tape Betacam SP (Sony) - ½” tape – industry standard pro. format - Component industry standard pro. format - Component

YUVYUV– Separate channels for Y, U and VSeparate channels for Y, U and V– 20 minutes recording on two-hour Betamax 20 minutes recording on two-hour Betamax

tapetape– three video signal tracks and four audio tracksthree video signal tracks and four audio tracks– very high image quality very high image quality – resolve 550 linesresolve 550 lines

CCIR 601CCIR 601

Most digital formats conform to ITU-R Most digital formats conform to ITU-R Recommendation BT 601 (commonly Recommendation BT 601 (commonly known as CCIR 601)known as CCIR 601)

See See http://http://en.wikipedia.org/wiki/CCIR_601en.wikipedia.org/wiki/CCIR_601

CCIR 601 is a family of formats - each written CCIR 601 is a family of formats - each written l:m:n l:m:n – that define sampling for digital video – that define sampling for digital video as YUV component videoas YUV component video

Defines sampling rates relative to a basic rate Defines sampling rates relative to a basic rate of 3.375MHzof 3.375MHz

CCIR contCCIR cont

ll is the no. times base rate that luminance is is the no. times base rate that luminance is sampled sampled

m m andand n. n. represent the relative manner in represent the relative manner in which colour differences are sampled which colour differences are sampled horizontally and vertically – chrominance horizontally and vertically – chrominance sub-samplingsub-sampling

e.g., 4:2:2 means luminance is sampled at e.g., 4:2:2 means luminance is sampled at 13.5MHz; both colour differences are sample 13.5MHz; both colour differences are sample for every other pixelfor every other pixel– 4:2:2 means that 720 luminance samples and two lots 4:2:2 means that 720 luminance samples and two lots

of 360 colour difference samples per lineof 360 colour difference samples per line– 4:2:0 means that 720 luminance samples per line and 4:2:0 means that 720 luminance samples per line and

two lots of 360 colour difference samples every other two lots of 360 colour difference samples every other lineline

– 4:1:1 means that 720 luminance samples and two lots 4:1:1 means that 720 luminance samples and two lots of 180 colour difference samples per lineof 180 colour difference samples per line

the no. of lines sampled is 576 for PAL and 480 the no. of lines sampled is 576 for PAL and 480 for NTSCfor NTSC

Are Pixels Round Are Pixels Round or Square?or Square?

The assumption (as a matter of convenience) The assumption (as a matter of convenience) that TV screens are 4:3 implies that for that TV screens are 4:3 implies that for square pixels 4/3 times as many values must square pixels 4/3 times as many values must be recorded for each line as there are lines be recorded for each line as there are lines making up the picturemaking up the picture

To sample an analogue video frame so as to To sample an analogue video frame so as to obtain square pixels requires that the obtain square pixels requires that the sampling rate is different for PAL and NTSCsampling rate is different for PAL and NTSC

Round and Round and square pixelssquare pixels

– sampling all 288 PAL lines in each field takes sampling all 288 PAL lines in each field takes 1/50s as opposed to 1/60s for the 240 NTSC 1/50s as opposed to 1/60s for the 240 NTSC lines, so each line takes exactly the same lines, so each line takes exactly the same time to sampletime to sample

– i.e., a PAL line’s samples, 768, are made in i.e., a PAL line’s samples, 768, are made in the same time as an NTSC line’s samples, the same time as an NTSC line’s samples, 640, so the PAL sampling rate is higher.640, so the PAL sampling rate is higher.

– this produces video suitable for playback on a this produces video suitable for playback on a computer monitor using a 4:3 resolution, i.e., computer monitor using a 4:3 resolution, i.e., 640 x 480, 1024 x768 but not 1280 x 1024640 x 480, 1024 x768 but not 1280 x 1024

Capturing analogue Capturing analogue video vs DVvideo vs DV

Capture of analogue video is normally done Capture of analogue video is normally done using square pixelsusing square pixels

Recording using a Digital video camera is Recording using a Digital video camera is normally done using CCIR 601 pixelsnormally done using CCIR 601 pixels

Some video capture cards will allow you to Some video capture cards will allow you to capture analogue video with nominally capture analogue video with nominally CCIR 601 pixelsCCIR 601 pixels

See See http://www.mir.com/DMG/aspect.htmlhttp://www.mir.com/DMG/aspect.html

CCIR non square CCIR non square pixelspixels

CCIR 601 pixels are not square. They are the CCIR 601 pixels are not square. They are the result of sampling both PAL and NTSC lines result of sampling both PAL and NTSC lines at the same rate taking 720 samples for at the same rate taking 720 samples for eacheach– i.e. a PAL line’s samples are a smaller proportion i.e. a PAL line’s samples are a smaller proportion

of the nominal resolution of PAL analogue video of the nominal resolution of PAL analogue video (768 (768 576) than an NTSC line’s (720 576) than an NTSC line’s (720 480) 480) sample are sample are

– thus CCIR 601 pixels for PAL are slightly wider thus CCIR 601 pixels for PAL are slightly wider and for NTSC are slightly narrower than squareand for NTSC are slightly narrower than square

NTSC/PAL v CCIRNTSC/PAL v CCIR

– Ratio is NTSC Ratio is NTSC 10:11 and PAL is 59:5410:11 and PAL is 59:54

– this produces video suitable for playback this produces video suitable for playback on the appropriate TV system, it appears on the appropriate TV system, it appears narrower (PAL) or wider (NTSC) by about narrower (PAL) or wider (NTSC) by about 10% when played back on a computer 10% when played back on a computer monitor using a 4:3 resolutionmonitor using a 4:3 resolution

Digital Tape Digital Tape FormatsFormats

D-1 (Sony, BTS) - ¾” (19mm) tapeD-1 (Sony, BTS) - ¾” (19mm) tape– 720 720 480 – 168Mb/s 480 – 168Mb/s– component video; YUVcomponent video; YUV– CCIR 601; 4:2:2CCIR 601; 4:2:2– 8-bits per component8-bits per component– broadcastbroadcast Standard Standard

D-2 (Ampex, Sony) - ¾” tapeD-2 (Ampex, Sony) - ¾” tape– Y/C digital - 8-bitY/C digital - 8-bit

D-3 (Panasonic) - ½” (12.7mm) tapeD-3 (Panasonic) - ½” (12.7mm) tape– Y/C digital - 8-bitY/C digital - 8-bit

Digital Tape Digital Tape Formats 2Formats 2

D-5 (Panasonic) - ½” tapeD-5 (Panasonic) - ½” tape– YUV - derived from D-3 - 10-bits per component ; YUV - derived from D-3 - 10-bits per component ;

2:1 compressed2:1 compressed– CCIR 601 4:2:2 CCIR 601 4:2:2 – broadcast Standardbroadcast Standard

DCT (Digital Component Technology - Ampex) - DCT (Digital Component Technology - Ampex) - ¾”tape¾”tape– YUV - derived from D-2 - 10-bits per component; YUV - derived from D-2 - 10-bits per component;

2:1 compression2:1 compression– CCIR 601 4:2:2CCIR 601 4:2:2– broadcast Standardbroadcast Standard

Digital Tape Digital Tape Formats 3Formats 3

DVCPRO (Panasonic)DVCPRO (Panasonic)

– DV with wider faster-running tape holding DV with wider faster-running tape holding additional analogue recording and control trackadditional analogue recording and control track

DVCAM (Sony)DVCAM (Sony)

– DV with high faster-running quality tapeDV with high faster-running quality tapeDigital Betacam (Sony, BTS) - ½” tapeDigital Betacam (Sony, BTS) - ½” tape

– YUV - 10-bits per component; 2:1 compressionYUV - 10-bits per component; 2:1 compression– CCIR 601 4:2:2CCIR 601 4:2:2– broadcast Standardbroadcast Standard

Digital Tape Digital Tape Formats 4Formats 4

Digital8 (Sony)Digital8 (Sony)– DV using Video8 or Hi8 tapesDV using Video8 or Hi8 tapes

DVCPRO50 (Panasonic)DVCPRO50 (Panasonic)– DV with high quality tapeDV with high quality tape– 4:2:24:2:2– uses two DV codecs in parallel uses two DV codecs in parallel – 50 Mbps (video) compressed about 3.3:150 Mbps (video) compressed about 3.3:1– visually lossless and high qualityvisually lossless and high quality

D-9 formerly Digital-S (JVC)D-9 formerly Digital-S (JVC)– Variant of DVVariant of DV– 4:2:24:2:2– uses two DV codecs in paralleluses two DV codecs in parallel– 50 Mbps (video) compressed about 3.3:150 Mbps (video) compressed about 3.3:1– visually lossless and high qualityvisually lossless and high quality

Digital Tape Digital Tape Formats 5Formats 5

DVC (Digital Video Cassette) or DV ¼” DVC (Digital Video Cassette) or DV ¼” (6.35mm) tape(6.35mm) tape– nominal 25 Mbit/s data stream (now also 50 and nominal 25 Mbit/s data stream (now also 50 and

100Mbps)100Mbps)

– can record up to three hours of video in SP can record up to three hours of video in SP (standard play) mode on cassettes which measure (standard play) mode on cassettes which measure 125x78x14.6mm125x78x14.6mm

– using MiniDV format cassettes - 1/12th the size of using MiniDV format cassettes - 1/12th the size of a standard VHS tape can record an hour in a standard VHS tape can record an hour in standard format or up to 90 minutes of lower standard format or up to 90 minutes of lower quality output in LPquality output in LP

Other Video Other Video FormatsFormats

DVC - DV contDVC - DV cont– PAL DV - CCIR 601 4:2:0 - 8-bits per PAL DV - CCIR 601 4:2:0 - 8-bits per

component; 5:1 compressedcomponent; 5:1 compressed– DV compression is directly done by the DV compression is directly done by the

DV camcorder using the DV codecDV camcorder using the DV codec

VideoCDVideoCD

– A competitor to VHS tapes – successful in the A competitor to VHS tapes – successful in the AsiaAsia

– Format defined 1993 – quite complexFormat defined 1993 – quite complex– Use MPEG-1 compressed videoUse MPEG-1 compressed video– Can accommodate multiple sound tracksCan accommodate multiple sound tracks

Other video Other video formatsformats

– Usually utilise proprietary formatsUsually utilise proprietary formatsSony MicroMV formatSony MicroMV format

Half the size of a MiniDV cassetteHalf the size of a MiniDV cassette

Uses MPEG 2 recording so lower quality than DVUses MPEG 2 recording so lower quality than DV

Recently abandoned by SonyRecently abandoned by Sony

– Some tapeless camcorders use flash memory Some tapeless camcorders use flash memory usually using MPEG4 Compressionusually using MPEG4 Compression

Other formatsOther formats

Apple QuickTime – MoviesApple QuickTime – Movies– interleaved format – (.MOV)interleaved format – (.MOV)

Frames of video and sound are interspersedFrames of video and sound are interspersed

Microsoft's Video for WindowsMicrosoft's Video for Windows– Audio Visual Interleave – (.AVI)Audio Visual Interleave – (.AVI)

– Being superseded by Active Streaming Format – Being superseded by Active Streaming Format – (.ASF) and windows media video (.WMV)(.ASF) and windows media video (.WMV)