High Definition Video: Acquisition to Broadcast

High Definition Video: Acquisition to Broadcast

Overview

• Defining the term “High Definition”• Pixel, frame and video formats• Image acquisition• Storage media• Compression• Post production• Transmission and the digital

switchover• Reception and “HD Ready”• Home entertainment HD

What is HD?

• Anything providing more resolution than current standard definition (SD) video.

• It is a generic term for “better”• It doesn’t specify how much better.

Standard definition

• For the UK, a system known as PAL• Broadcast systems comprising 625

lines• 25 frames per second• After signalling and data removed, a

frame resolution of 768x576 pixels• Frame aspect of 4:3 (768:576

simplified to it’s lowest common factor)

Standard definition

SD, 4:3

4

3

768

576

Standard definition

• 768x576 assumes a square pixel• Pixels don’t have to be square and in

SD video, they usually aren’t!• 4:3 PAL uses a pixel aspect of

1.066666:1• Your TV “stretches” the frame

horizontally• Anything that increases the size of a

pixel reduces resolution

Standard definitionStandard definition

4

3

Widescreen

• A further extension of this kludge• Very un-square pixels• 16:9 broadcasts take the 720x576

frame and stretch it even more horizontally

Standard definitionWidescreen standard definition

4

3

16

9

Standard definition

• Uses anamorphic pixels• 4:3 – 1.0666:1• 16:9 – 1.4222:1• Results in resolution being lost due

to the stretching process

High Definition

• Two common formats– 720p– 1080i

• SD frame: 720 x 576• 720p frame: 1280 x 720 (2.2 x SD)• 1080i frame: 1920 x 1080 (5 x SD)

High Definition

1920x1080i, 16:9

1280x720p, 16:9

SD 720x576, 4:3

High Definition(or “what all the fuss is about”)

• 1080i provides almost five times the resolution of Standard Definition

• Unencumbered by legacy technology• Native 16:9 aspect ratio• True 720p and 1080i are square pixel

formats – no resolution-killing scaling when displayed

Image Acquisition

• Professional: anything with mechanical manual focus

• “Prosumer” – Servo-operated focus / fixed lenses that provide similar functionality to pro cameras

• Consumer - point-and-shoot cameras that do all of the hard work for you!

Professional camerasUnlimited budget

ARRI 320D•Can shoot film resolutions•CCD is the same size as a 35mm frame•Needs a huge amount of peripherals•Camera alone starts at £200,000•Lenses £20,000 upwards

Professional cameras


•Native 1080p•Variable frame rates (1 to 60fps)•Still needs lots of peripherals•Camera alone starts at £80,000

Top-end

HDC-1500L444

Professional camerasMainstream HD

HDW-F900R

•Native 1080i•Integral HDCAM recorder•More realistic price: £40,000


Optical storage

PDW-F350

•Native 1080i•Integral ProDisc recorder•£10,000


Budget professional

JVC GY-HD251E

•Native 1080i•Integral 720p HDV recorder•Still uses “proper” lenses•£5000

“Prosumer” cameras

Canon XHA1

•Native 1080i•Integral 1080i HDV recorder•Internal focus lens•£2200

“Prosumer” cameras

Sony HVR-V1E•Native 1080i•Integral 1080i HDV recorder•Internal focus lens•£1500

Consumer camerasSony HDR-HC7E


Consumer camerasCanon HV20


Consumer cameras

SanyoDMX-HD1000

•Native 1080i•Uses standard SD flash storage•4.2 megapixel stills•£450

Consumer cameras

Image Acquisition

• For home use, size and convenience are generally more important than features

• “More expensive” doesn’t necessarily mean “better” or “more suited”

• The manual functions on pro cameras just get in the way when you’re simply trying to shoot something

Image Acquisition

Lens

Image sensor

Processing electronics

Storage

Image Acquisition

Video storage

• Tape• Optical disc• Hard drives• Flash memory

Video Tape Recorders




Principal HD tape formats

Tape: pros

• Relatively cheap• Universally accepted for interchange• Long shelf life when stored correctly• Long recording durations

Tape: cons

• Linear by nature• Limited record / playback cycles• No warning during recording of drop-

out• Easily damaged if handled carelessly• Easily damaged by deck malfunction• Easily damaged by incorrect storage• Decks can be very expensive to

maintain

Tape: cons

Deck malfunction Incorrect storage

Tape: cons

• Linear by nature• Limited record / playback cycles• No warning during recording of drop-

out• Easily damaged if handled carelessly• Easily damaged by deck malfunction• Easily damaged by incorrect storage• Decks can be very expensive to

maintain

Tape: cons

Video storage: TapeQ:Who won the VHS vs. Beta format war?A: Sony’s Beta!

•Betacam SP•Betacam SX•MPEG IMX•Digital Betacam•HDCAM•HDCAM SR

Video storage: Tape

Video storage: optical disc

Optical disc: pros

• Robust• High number of read/write cycles• Non-linear: near instant access• Easy ingest to editing systems• Improved workflow• Supports multiple formats (SD & HD)

Optical disc: cons

• Read/write cycles not as high as expected

• Harsh conditions can upset recording• Limited shelf-life – data degrades with

time

Video storage: hard discs

Hard drives: pros

• Fast – capable of recording uncompressed

• Non-linear – instant access• Capacity – multi-terrabyte• Unlimited read/write cycles• Immediate ingest

Hard drives: cons

• Not portable• Camera-to-drive interfaces can be

costly• Failures often catastrophic• Not practical for long-term storage• Can be noisy

Video storage: hard discs

Video storage: flash



Flash: pros• Fast – capable of recording

uncompressed• Non-linear – instant access• Portable, compact, light• Incredibly robust• High number of read/write cycles• Immediate ingest• Hot-swap of cards• Can be stored practically indefinitely• Cheap for consumer flash

Flash: cons

• Limited capacity• Often used in conjunction with HDD• Very expensive for pro grade flash• Not cost-effective for long-term

storage

Video compression

• Video is big!

Data rates for common formats

SD 720/25P 1080/25P 2K 4K0

100

200

300

400

500

600

700

800

900

1000

14.8343.95

98.88

216

864

MB/sec

Exponential (MB/sec)

Video compression

• Video is very big• Most storage media can not handle

this

How to reduce data rates?

• Lower image resolution• Remove image information• Encode image information more

efficiently

The compression compromise Low compression

High data rateHigh quality

Short runtime

High compressionLow data rateLow qualityLong runtime

HDV compression

1920x10801:1PA16BPP1:1CR25FPS= 99MB/sec

1440x10801.333:1PA16BPP1:1CR25FPS= 74MB/sec

140x10801.333:1PA12BPP1:1CR25FPS= 55MB/sec

1440x10801.333:1PA12BPP17:125FPS= 3MB/sec

Downsample

Requantise

Compress

Final output is only 3% of original!

Post Production

Edit suites

• HD presents a big challenge for computers

• 5 x the resolution means 5 x the time• Heavy compression causes quality

problems

Problems with compression

• Editing can not be performed on compressed frames

• Each frame must be uncompressed• The frame is modified• The resulting frame is recompressed• All intermediate stages should remain

uncompressed to maintain quality• Very similar to analogue video

generation loss during duplication

Uncompressed editing?

• Essential for top-end production• Often unrealistic for mid- to low-budget

productions and home use• Storage demands can be staggering

– A real-time fade needs 200 MB/sec!

• Not a realistic prospect with easily accessible / affordable equipment

• All UK mainland terrestrial analogue TV transmissions will cease by the end of 2012

• Central switchover in 2011• Three to six digital TV channels in place

of one analogue channel• Not guaranteed that spectrum freed by

analogue switch-off will be used for TV• Digital does not mean high definition!

3 ways of receiving digital HD

Is it real HD?• Very nearly • SkyHD digibox outputs a 1920x1080i

signal• It receives a 1440x1080i transmission• Anamorphic pixels, so we’re loosing

resolution again• Highly compressed• Far better than SD and appreciably

better than 720p• All channels are equal, but some

channels are more equal than others…

And the quality?

• Surprisingly good!• MPEG-4• 46 megabit/sec transponders• Up to 15 megabit/sec per channel• Subjectively similar to HD-DVD or

BluRay

• Does not mean it actually displays true HD

• Simply means it can accept an HD signal

• Only the specifications will reveal what the TV is natively capable of

TV Specifications• Check the panel’s native resolution• This is the actual number of pixels

contained in the display• Values below your intended format

means the you’re throwing resolution away

• Differences – above or below – mean scaling

Image scaling

• The display is generating a new image to fit its display size

• Professional equipment to do the same job costs tens of thousands of pounds

• Your TV probably costs less than £2000

TV Specifications

• Aim for a TV that has a native resolution of 1920 x 1080 – this will handle all frame sizes

• TVs with a lower resolution are not necessarily bad, just remember you’re not seeing as much as you could

Home entertainment HD

HD Interconnects

• HD isn’t necessarily digital!• Three popular formats

HD Interconnects

Analogue component

HDMI

DVI

HD Interconnects• They don’t need to be expensive• Most high-street stores charge

astronomical prices for HD interconnects

• For short runs, you do not need nitrogen-filled, gold plated, double-helix, oxygen-free-copper-cored cables.

• eBay is your friend!

HD Interconnects

HD Interconnects

Home entertainment HD

HDCP• High-bandwidth Digital Content Protection• Designed by Intel

HDCP negotiation

HD Content

Downsampled SD

HDCP• Vast majority of HD-ready TVs and

most computer panels support HDCP• Worth checking if you…

– Are running Windows Vista or MacOS X– Have a BluRay or HD-DVD drive installed– Intend to watch HD movies on your PC or

Mac

• Can be present on HDMI and DVI• Only a problem if your source wants to

negotiate an HDCP-protected session

HDCP and home entertainment• HD-DVD, BluRay, HD set top boxes,

XBox360 and PlayStation 3 all require an HDCP-compliant target

• Every device in the chain must support HDCP encryption– Switchers– AV amplifiers– Distribution boxes– TVs and monitors

Any questions?

Documents

High Definition Video: Acquisition to Broadcast