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Everything You (N)Ever Wanted to Know About HDTV
Intro
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)
High-Definition (Hi-Def)
720 = 1280 × 720
1080 = 1920 × 1080
Enhanced Definition (EDTV)
Computer monitors usually have higher resolution than TVs
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
Letter "p" or "i" is often added to the resolution
Letter "p" or "i" is sometimes added to the refresh rate
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
Many movies are wider than 16:9
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 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
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)
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
Uses YIQ color space (similar to YUV)
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
Video: MPEG-2
8-bit quantization
4:2:0 YCbCr chroma sub-sampling
Audio: AC-3 (Dolby Digital, 5.1 channels)
Closed Captioning: EIA-708
Modulation
8VSB
VSB = Vestigial Side-Band
Refinement of amplitude modulation (AM)
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
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
Cable
Most cable companies carry HD channels
Uses 256-QAM modulation instead of 8SVB
Many newer HDTV tuners include support for 256-QAM in addition to 8VSB
Most of the HD channels are encrypted on most cable systems
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
DVB-S2 - newer satellite standard
Display Technologies
Future Display Technologies
OLED (organic light-emitting diodes)
FED (Field-emission display)
SED (Surface-conduction electron-emitter display)
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
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Cables and Connectors
Composite - 1 cable caries all video info
S-Video - 4-pin cable separates luma and chroma signals
Component - 3 RCA cables carry luma and 2 chroma signals
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)
SingleLink vs DualLink variants
HDMI - High-Definition Multimedia Interface
Cheap cables work fine
Antennas
HDTV signals come in over UHF
ATSC is more susceptible to interference and low signals
When reception is too poor, you'll almost always get NO picture
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
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
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
Choice of display technologies is largely personal preference
As with any technology, wait as long as possible to buy
You should really look at the screen in person before buying
Beware HD Ready, unless you already have a (cable, satellite, or ATSC) tuner
Multiple DVI and/or HDMI connectors are desirable
Try to get support for QAM in the tuner
Try to get support for CableCARD 2
PCs and HDTV
GNU/Linux and HDTV
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KnoppMyth
MythDora
Mythbuntu
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LinuxMCE
SageTV
Video capture cards
Macs and HDTV
Front Row
Apple TV
EyeTV
Video capture cards
Broadcast Flag
Transport stream has a bit/flag saying "don't allow copying this video"
Receivers must adhere to the flag
Applies mainly to PVRs and other video recorders
Makes it difficult/impossible to use Open Source / Free Software
FCC has pushed back the deadline for requiring adherence
Analog TV Shut-off
February 17, 2009
Congressionally mandated date to stop NTSC broadcast transmissions
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
Future Standards
Summary
Digital (DTV) and hi-def (HDTV) are orthogonal concepts
HDTV is 720p or 1080i
DTV over the air is called ATSC
As with any technology, wait as long as possible to buy
Do some research before buying an HDTV
Further Exploration
Color gamut
Color spaces
Color calibration, gamma
Modulation details
Carrier signals
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.
Presentation Info
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