Everything You (N)Ever Wanted to Know About HDTV

Intro

  • Craig Buchek
    • BoochTek, LLC - web development
    • Chair of St. Louis LUG for many years
  • I run my TV through a Mac, which displays to a 30" LCD monitor
    • Elgato tuner
    • EyeTV

Why HDTV at a Linux Meeting?

This presentation came about due to an after-meeting discussion. We were talking about HDTV, and I was explaining several of the concepts. Someone (Gary Meyer, I think) mentioned that it would make an excellent presentation at one of our meetings.

Basic Definitions

  • Pixels - picture elements (dots on the screen)
  • Resolution - how many pixels make up the screen
  • Aspect ratio - ratio of picture's width to height
  • Modulation - how (digital) signals get put onto an analog carrier signal for transmission
  • Encoding/decoding - how digital information is arranged and interpreted
  • Multiplexing - putting multiple streams of data into a single stream

Resolutions

  • Standard Definition (SDTV)
    • 480 = 640 × 480 (square pixels) or 704 × 480 (non-square pixels)
  • High-Definition (Hi-Def)
    • 720 = 1280 × 720
    • 1080 = 1920 × 1080
  • Enhanced Definition (EDTV)
    • 480p or better, but less than 720p
  • Computer monitors usually have higher resolution than TVs
    • Typically 1440 × 900 or 1280 × 1024 these days
  • Horizontal resolution (pixels per line) is often omitted in HDTV specs

Refresh Rates

  • Frames per second
  • 24 - most movies
  • 29.97 - current analog TV
  • 50 - European TV
  • 60 - most HDTV
  • PC monitors can handle a wide variety of refresh rates (multi-sync)
  • Most PC display modes are 60, 72, 75, or 85 frames/sec

Progressive vs. Interlaced

  • Interlaced - alternates between showing all the odd lines, then all the even lines
    • Shifts half a line between showing each set
    • Hopefully fast enough that you won't notice
    • Sometimes leads to flicker, especially when viewing narrow horizontal lines
    • Can lead to artifacts when pausing an interlaced signal
  • Progressive scan - every line shown in order
    • Obviously this is preferred
    • All PC monitors since about 1990 are progressive-scan
  • Letter "p" or "i" is often added to the resolution
    • 480i, 480p, 720p, 1080i
  • Letter "p" or "i" is sometimes added to the refresh rate
    • 24p, 30p, 60i, 60p

Aspect Ratios

  • Standard TV - 4:3
  • Wide-Screen - 16:9
  • Viewing wide-screen video on 4:3 screen requires "letter-boxing"
  • Viewing standard 4:3 video on a wide screen requires "pillar-boxing"
  • Most wide-screen monitors (and some HDTVs) are 16:10
    • A little taller than 16:9
    • Good compromise when viewing both 4:3 and wide-screen sources
  • Many movies are wider than 16:9
    • So you'll still get some letter-boxing on wide-screen TV

Digital vs. Hi-Def

  • Digital (DTV) and hi-def (HDTV) are orthogonal concepts
  • You can have DTV that is not hi-def
  • You could theoretically have analog high-definition video
    • Analog movie-theater film could be considered hi-def

Analog TV (NTSC)

  • NTSC = National Television System(s) Committee
  • Used in most of the Americas, Japan, South Korea, and the Philippines
  • Other countries use PAL or SECAM
  • Approximates 480 × 704 interlaced resolution
  • Audio is on completely different frequency than the video

NTSC Details

  • 484 lines shown on screen (of 525 broadcast)
    • Other lines used for sync, vertical retrace, and data such as captioning
  • No defined horizontal resolution
    • Because it's analog
  • 4:3 aspect ratio
    • Pixels need not be square
  • Interlaced
    • 2 fields per frame
    • 262.5 lines/field
  • 29.97 frames/sec
    • 59.94 fields/sec
    • Was exactly 60 fields/sec before color was added
      • Changed by 0.1% due to color "beating" w/ audio sub-carrier

It was preferable to match the screen refresh rate to the power source to avoid wave interference that would produce rolling bars on the screen. Synchronization of the refresh rate to the power cycle also helped kinescope cameras record early live television broadcasts, as it was very simple to synchronize a film camera to capture one frame of video on each film frame by using the alternating current frequency as a shutter trigger.

Color TV (NTSC)

  • Luminance-chrominance (Y/C)
    • S-Video connector puts them on separate wires
  • Original black-and-white signal had only a luminance signal
  • Color information is 90 degrees out of phase with the luminance signal
  • Color burst after each line signals which is the color sub-carrier
  • Field sync also added to color sub-carrier
    • TVs can actually handle 60i, 30p, and 24p signals (maybe?)
  • Uses YIQ color space (similar to YUV)
    • Although almost all TVs cheat and use R-Y and B-Y
  • TVs convert YIQ to RGB, which is used by the CRT guns

The eye is more sensitive to changes in the orange-blue (I) range than in the purple-green range (Q) — therefore less bandwidth is required for Q than for I. Broadcast NTSC limits I to 1.3 MHz and Q to 0.4 MHz. I and Q are frequency interleaved into the 4 MHz Y signal, which keeps the bandwidth of the overall signal down to 4.2 MHz.

NTSC saves only 11% of the original blue and 30% of the red. The green information is usually preserved in the Y channel.

Digital TV (ATSC)

  • ATSC = Advanced Television Systems Committee
  • Lots of different formats (18 or 28, depending who you ask)
    • 3 resolutions (480, 720, 1080)
    • various refresh rates (23.976 - 60 frames/sec)
    • 4:3 or 16:9 wide-screen
    • progressive or interlaced

ATSC Encoding

  • Modulation: 8VSB
    • 6 MHz of bandwidth per channel (same as NTSC)
    • 19.39 Mb/s
  • Multiplexing: MPEG-2 (transport stream) 188-byte packets
    • Allows multiple sub-channels (sub-streams) within a single stream/channel
  • Video: MPEG-2
    • 8-bit quantization
    • 4:2:0 YCbCr chroma sub-sampling
  • Audio: AC-3 (Dolby Digital, 5.1 channels)
    • Note that this is NOT an MPEG-2 audio format
  • Closed Captioning: EIA-708

Modulation

  • 8VSB
  • VSB = Vestigial Side-Band
    • A side-band that has been only partly cut off or suppressed
  • Refinement of amplitude modulation (AM)
    • More efficiently uses electrical power and bandwidth
  • Chosen due to efficient use of bandwidth
    • So existing 6 MHz TV channels could be used

Receivers must sample the incoming signal at very precise intervals to properly interpret the 8-level signal. Improper timing results in receiving useless information, so this makes reception in moving vehicles nearly impossible due to the Doppler effect.

Multiplexing

  • There's 19 Mbps (6 MHz) of bandwidth per ATSC channel
    • Actually less, due to error correction and overhead
  • Different formats require different amounts of bandwidth
  • Can put (up to 6) multiple sub-channels into a single channel
  • Bandwidth of sub-channels has to add up to less than 19 Mbps
  • Our local PBS station has 4 sub-channels:
    • Primary content (copy of analog broadcast, appears to be 480p)
    • Hi-def (sometimes a hi-def version of primary sub-channel, often a nature program)
    • Kids programming
    • DIY channel

Video Codecs

  • MPEG-2
  • MPEG = Motion Picture Experts Group
    • Standards for video (and audio) codecs, compression, containers, streams, et
  • 4:2:0 YCbCr color space
    • Three quarters of the chrominance values have been deleted

Cable

  • Most cable companies carry HD channels
  • Uses 256-QAM modulation instead of 8SVB
    • Some cable companies may use 16-VSB
  • Many newer HDTV tuners include support for 256-QAM in addition to 8VSB
  • Most of the HD channels are encrypted on most cable systems
    • Oddly, video on demand (VOD) is not yet encrypted by most cable systems, and you can see what other people are watching via a QAM tuner

Satellite

  • Dish Network and DirecTV carry HD channels
  • They use their own tuners
  • Signals are not compatible with HDTV tuners
  • Output of their receivers/tuners can be sent to an HDTV display

DVB

  • Digital Video Broadcasting
  • Standard used in Europe and elsewhere
  • DVB-T - terrestrial
  • DVB-C - cable
  • DVB-S - satellite
    • Used by US some satellite systems as well (Dish Network)
  • DVB-S2 - newer satellite standard
    • HDTV, MPEG4/H.264

Display Technologies

  • LCD (liquid crystal display)
  • Plasma
    • Larger sizes
    • More expensive
    • Lower resolutions
    • Possible burn-in issues still?
    • Excellent color saturation
  • CRT (cathode ray tube)
  • DLP/LCoS (digital light projection / liquid crystal on silicon)
  • Rear projection
  • Projector

Future Display Technologies

  • OLED (organic light-emitting diodes)
  • FED (Field-emission display)
  • SED (Surface-conduction electron-emitter display)
    • Like a mini-CRT for each pixel

HD Ready

  • HD Ready refers to any display that is capable of accepting and displaying a high-definition signal at either 720p, 1080i or 1080p using a component video or digital input, and does not have a built-in HD-capable tuner.

CableCARD

  • PCMCIA card for decrypting protected MPEG video streams
  • Authenticates and authorizes the set of channels you've paid for
  • Very similar to decryption cards used in satellite receivers
  • Plugs into ATSC tuner (stand-alone, integrated into TV, TiVo, etc.)
  • CableCARD 2.0 coming soon
    • Adds interactivity: pay-per view (PPV), video on demand (VOD), etc.
    • Requires that tuner support CableCARD 2.0
  • See this excellent Ars Technica article

Cables and Connectors

  • Composite - 1 cable caries all video info
    • RCA cable, often yellow
  • S-Video - 4-pin cable separates luma and chroma signals
  • Component - 3 RCA cables carry luma and 2 chroma signals
    • YPbPr - analog
    • YCbCr - digital
    • RCA cables are red, green, and blue, but they do not carry RGB
  • DVI - Digital Video Interface
    • PC standard for digital monitors, also used for HDTV
    • Cable can carry digital or VGA-compatible analog
    • Supports High-Bandwidth Digital Content Protection System (HDCP)
      • DRM capabilities
    • SingleLink vs DualLink variants
  • HDMI - High-Definition Multimedia Interface
    • Digital video plus digital audio
    • Video signal is compatible with DVI
  • Cheap cables work fine

Antennas

  • HDTV signals come in over UHF
    • Except for 2 cities in the US, which have ATSC VHF channels
  • ATSC is more susceptible to interference and low signals
  • When reception is too poor, you'll almost always get NO picture
    • Or picture will pause frequently
    • Cable seems to get pixelization artifacts instead
  • A regular UHF antenna is all that's required
    • A high-quality antenna is recommended
    • A powered amplifier is useful, especially if you split the signal
  • Pointing the antenna towards the TV tower is important
    • Go to AntennaWeb.org to determine where to point it, and what kind to get
    • Most St. Louis stations' towers are located in South County
  • AntennasDirect is a local company that makes and sells the most highly-regarded antennas

Buying a TV

  • All TVs today (except small sizes) must come with a digital tuner
    • Manufacturers get around this by selling "monitors" instead of TVs
  • Stick with one of the native resolutions (720p or 1080i)
    • Or 1080p, which is the best you can get
    • 1280 × 768 is OK; it'll just not use 48 of the lines
    • 1368 × 768 and 1024 × 1024 don't seem like a good idea to me
      • Requires interpolation with numbers that don;t round easily
  • Choice of display technologies is largely personal preference
    • I prefer LCD; can't wait to see OLED, FED, and SED
  • As with any technology, wait as long as possible to buy
    • Things get cheaper over time
    • New technologies get better all the time
  • You should really look at the screen in person before buying
    • Make sure you adjust the settings of the screens you look at
  • Beware HD Ready, unless you already have a (cable, satellite, or ATSC) tuner
  • Multiple DVI and/or HDMI connectors are desirable
    • Also Component connectors if your DVD player has that but no DVI/HDMI
  • Try to get support for QAM in the tuner
  • Try to get support for CableCARD 2

PCs and HDTV

  • HTPC - Home Theater PC
    • PC purpose-built for home theater
    • Special cases (low noise, VFD displays)
    • Special software (interfaces that can be read from the couch)
  • Windows Media Center Edition (MCE)
  • MediaPortal (Windows, Open Source)
  • Video capture cards
    • Hauppauge
    • ATI

GNU/Linux and HDTV

  • MythTV
    • KnoppMyth
    • MythDora
    • Mythbuntu
  • Freevo
  • LinuxMCE
  • SageTV
  • Video capture cards
    • Hauppauge
    • pcHDTV - supports QAM now

Macs and HDTV

  • Front Row
  • Apple TV
  • EyeTV
  • Video capture cards
    • Elgato

Broadcast Flag

  • Transport stream has a bit/flag saying "don't allow copying this video"
  • Receivers must adhere to the flag
    • Only due to legal/regulatory mandate
  • Applies mainly to PVRs and other video recorders
    • Allows time-shifting, but not backups or moving to other devices
  • Makes it difficult/impossible to use Open Source / Free Software
    • Because users could just turn it off in the source and recompile
  • FCC has pushed back the deadline for requiring adherence

Analog TV Shut-off

  • February 17, 2009
  • Congressionally mandated date to stop NTSC broadcast transmissions
    • Will free up VHF channels and UHF 52-69
    • Freed-up frequencies will be auctioned off
  • All terrestrial TV viewers will need to use digital tuners
  • VCRs, DVD recorders, and DVRs will also need to have ATSC tuners
  • Will probably get pushed back if too many people still need to convert
    • Taking TV away from Americans is not a smart political move!
    • Was originally set for early 2007

Future Standards

  • MPEG-4 / H.264
  • 1080p
  • Ultra High Definition Television (UHDTV)
    • Proposed 7680 × 4320, 60p, 22.2 audio channels, 16:9
  • DisplayPort video connector

Summary

  • Digital (DTV) and hi-def (HDTV) are orthogonal concepts
    • The switch to digital does not mean all broadcasts will be hi-def
  • HDTV is 720p or 1080i
  • DTV over the air is called ATSC
    • ATSC allows multiple sub-channels
  • As with any technology, wait as long as possible to buy
    • Prices drop, and new technologies continue to appear
  • Do some research before buying an HDTV

Further Exploration

  • Color gamut
    • Color spaces
    • Color calibration, gamma
  • Modulation details
  • Carrier signals
    • Sub-carriers
    • Side-bands
  • Personal digital video recorders (PVR/DVR)
  • Digital audio broadcasting
    • HD Radio - hybrid digital, NOT hi-def!
    • Satellite radio (XM, Sirius)
    • Digital Radio Mondiale
    • Radio Data System - low-bandwidth, carries song/station info for FM stations
  • Studio/movie digital/hi-def standards

Resources

Credits

  • This presentation was written by Craig Buchek.
  • Some content was taken from the relevant Wikipedia articles.
  • Thanks to DokuWiki folks for the software I used to (slowly) build up the content.
  • Thanks to my girlfriend Beth for putting up with me while I worked on this.
    • And for putting up with having to navigate Mac software just to watch TV.

Presentation Info