question: Why there’s different content on TV, at the same time, on the same channel, based on HD/non-HD quality?
comment: I am unsure if this is the only reason, but certainly some of it has to do with the fact that many films/movies/shows - especially for something like NatGeo - are not of HD quality. The technology of even only 20 years ago, both in the filming and the viewing aspects, has changed immensely. It also likely has to do with the fact that - they can. Despite them being the 'same' channel, they are still individual channels with their own programming agendas - which may not mesh up with eachother.
passages: BULLET::::- Multiplexes can make use of statistical multiplexing at the MPEG video coder whereby the bitrate allocated to a channel within the multiplex can vary dynamically depending on how difficult it is to code the picture content at that precise time, and how much demand there is for bandwidth from other channels. In this way, complex pictures with much detail may demand a higher bitrate at one instant and this can result in the bitrate allocated to another channel in the same multiplex being reduced if the second channel is currently transmitting pictures which are easier to encode, with less fine detail.
   Section::::Effects.:High-definition television.
  
  High-definition television signals must also be simultaneously substituted, although this only applies if a local over-the-air digital transmitter that broadcasts HD content is receivable in the market served by the local cable provider. Since many broadcasters were only required to convert their main, typically major-market transmitters during the 2011 digital television transition in Canada, this means that HD simsubbing is not currently enforceable in many rural areas.
   Since the 1990s, the concept of flow has been threatened by new technologies and programming strategies that free the viewer from the old television model. VCRs, DVDs, DVRs (such as TiVo), Video-on-Demand, and online video sources all allow the viewer to construct their own flow. They are no longer limited to a choice of three or four networks, as they were in the 1950s–1960s. Consequently, the concept of flow is under attack and may not survive beyond the broadcast era of television.
  
  Section::::Production and purpose.
   In the US television programming market, cable and DBS/satellite operators compete against each other to deliver HDTV programming. An HDTV program requires much higher datarates (3-4x) than a standard-definition program. This places a huge burden on a service-operator, which must deliver a variety of programming (many channels), including increasing amounts of HDTV programming, over a resource-constrained distribution medium. Re-compression by cable/satellite operators is a technical necessity for carriage of diverse TV-programming over limited bandwidth capacity of the respective providers.
   Multi-standard television
  
  Multi-standard television sets were made for use in the television industry, so that one TV set or monitor could show video content from other television systems. Multistandard is only used with analogue television. In digital television, there are different standards, like DVB, ISDB, and ATSC. However digital multistandard tv set are not existing. Multistandard devices in digital TV may be PC extension card.
   In March 2011 the DPP created common technical standards for tape delivery of HDTV and SDTV programmes to all major UK broadcasters at the time. UK TV producers now have one set of guidelines that cover technical specifications, picture and sound quality for delivery to ITV, BBC, Channel 4, Sky, Channel 5, BT Sport and S4C.
   Section::::See also.
  
  TV transmission systems
  
  BULLET::::- Analog high-definition television systems
  
  BULLET::::- PAL, what MAC technology tried to replace
  
  BULLET::::- SECAM, what MAC technology tried to replace
  
  BULLET::::- A-MAC
  
  BULLET::::- B-MAC
  
  BULLET::::- C-MAC
  
  BULLET::::- D-MAC
  
  BULLET::::- E-MAC
  
  BULLET::::- S-MAC
  
  BULLET::::- D2-MAC
  
  BULLET::::- HD-MAC, an early high-definition television standard allowing for 2048×1152 resolution.
  
  BULLET::::- DVB-S, MAC technology was replaced by this standard
  
  BULLET::::- DVB-T, MAC technology was replaced by this standard
  
  Related standards:
  
  BULLET::::- NICAM-like audio coding is used in the HD-MAC system.
  
  BULLET::::- Chroma subsampling in TV indicated as 4:2:2, 4:1:1 etc...
  
  Section::::External links.
   BULLET::::- 0x04 - Content is Copy Once for digital output, but would have Macrovision 7 Day Unlimited restriction applied on the analog outputs. This affects content viewed either on an HDTV with component cabling or on a standard definition TV. It also affects content saved to VCR or DVD when the recorder is connected to an analog output on the DVR.†
   Section::::Influences in media systems.:Media capture.
   Section::::Stream quality.
   Section::::Canada.:Television.:Previous examples.
   BULLET::::- Less control. If a broadcaster prefers to limit access to their content based on regions, and would like good data on viewer behaviour, such as volume, trends and viewing time, then a traditional broadcasting solution offers more control.
   BULLET::::- TV Broadcast: April 12 & 19, 2019
  
  BULLET::::- Live Broadcast: April 20, 2019
  
  BULLET::::- TV Broadcast: April 26 & May 3, 2019
  
  BULLET::::- Live Broadcast: May 4, 2019
  
  BULLET::::- TV Broadcast: May 10 & 17, 2019
  
  BULLET::::- The number of broadcasting channels is reduced to four starting from this live broadcast.
  
  BULLET::::- Live Broadcast: May 18 & 19, 2019
  
  BULLET::::- TV Broadcast: May 24, 31 & June 7, 2019
  
  BULLET::::- For this live broadcast, the four channels will be done in a relay
  
  BULLET::::- First overseas live broadcast in Seasons 1 & 2 combined
   Digital cable channels are touted as being able to offer a higher quality picture than their analog counterparts. This is often true, with a dramatic improvement in chroma resolution (120 lines for NTSC versus 270 for digital). However, digital compression has a tendency to soften the quality of the television picture, particularly of channels that are more heavily compressed. Pixelation and other artifacts are often visible.
  
  Section::::Digital cable.:Set-top boxes.
   BULLET::::- Interoperability means that the same program and commercial content viewed using a television receiver can cross platforms and be viewed across a multiplicity of platforms/appliances, not just the TV, but also the PC, the mobile handset, the iPod, etc. From a technical standpoint, interoperability between media platforms "requires that all the media has to adopt the same fundamental compression scheme."
   The use of digital subchannels has been termed an "instant duopoly," because of the ease by which a single digital station can deliver multiple channels of programming from different networks at the same time. One station can carry four or more standard definition digital channels; multiple high definition feeds typically require too large a bitrate size to be carried on different subchannels of the same station simultaneously without loss of image quality.
  
  Section::::United States.:Virtual duopolies.
   Williams claims that flow is determined by television's "stage of development," but Rick Altman, Professor of Cinemas and Comparative Literature at the University of Iowa, argues that the culture of the medium produces and determines its flow. He notes that the soundtrack is unique to American culture and is one of the techniques that shapes the viewer's flow or his or her experience watching television. He notes that the soundtrack provides the viewer with sufficient plot, cues important events by sound (sound advance, e.g. clapping before it is seen on screen), and creates continuity. These sonic elements create an intermittent flow of television. The goal is not to get the viewers to watch carefully, but to keep them from turning the television off.
   Stream quality refers to the quality of the image and audio transferred from the servers of the distributor to the user's home screen. Higher-quality video such as video in high definition (720p+) requires higher bandwidth and faster connection speeds. The generally accepted kbit/s download rate needed to stream high-definition video that has been encoded with H.264 is 3500 kbit/s, whereas standard-definition television can range from 500 to 1500 kbit/s depending on the resolution on screen. In the UK, the BBC iPlayer deals with the largest amount of traffic yet it offers HD content along with SD content. As more people have gotten broadband connections which can deal with streaming HD video over the Internet, the BBC iPlayer has tried to keep up with demand and pace. However, as streaming HD video takes around 1.5 GB of data per hour of video the BBC has had to invest a lot of money collected from License Fee payers to implement this on a large scale.
   Each device may contain one or more HDCP transmitters and/or receivers. (A single transmitter or receiver chip may combine HDCP and HDMI functionality.)
   Many viewers in the Greater Toronto Area can pick up American stations from Buffalo, New York, over-the-air, as well as high-definition versions of the stations from both Buffalo and Seattle, Washington, on cable television. Similarly, cable television viewers in Greater Vancouver may receive unmatched HD stations from Detroit, Michigan, and Rochester, New York. However, high-definition feeds are also subject to simsub, and such substitutions began to increase as local broadcasters performed wider deployments of digital terrestrial television.
  
  Section::::Implementation and exceptions.:Rule changes and Super Bowl simsub ban.
   BULLET::::- HD-MAC, an early high-definition television standard allowing for 2048x1152 resolution.
  
  Section::::Studio (non-broadcast) MAC variants.
  
  S-MAC ("Studio MAC"): Used mostly in North America.
  
  BULLET::::- Processing NTSC component signals yields better results (a higher quality image) than manipulating NTSC directly – thus the need to create S-MAC.
  
  BULLET::::- It is not possible to mix standard MAC signals in the studio environment because the (R-Y) and (B-Y) components are carried on alternate lines.
  
  BULLET::::- S-MAC's SECAM like approach to bandwidth reduction is technical annoyance, but most studio users are not affected by it.
   The "UHD Alliance", an industry consortium of content creators, distributors, and hardware manufacturers, announced Monday on the 11th of January 2016 during CES 2016 press conference its "Ultra HD Premium" specification, which defines resolution, bit depth, color gamut, high-dynamic-range imaging (HDRI) and rendering (HDRR) required for Ultra HD (UHDTV) content and displays to carry their Ultra HD Premium logo.
   Section::::Digital television.
  
  Section::::Digital television.:Digital channels.
  
  The station's digital signal is multiplexed:
   Downconversion is usually required, hence very little image quality loss is perceived by viewers at the recommended viewing distance with most TV sets.
  
  Section::::Offline conversion.
  
  A lot of cross format television conversion is done offline. There are several DVD packages that offer offline PAL ↔ NTSC conversion – including cross conversion (technically MPEG ↔ DTV) from the myriad of MPEG-based web video formats.
   In January 2012 the DPP announced that these broadcasters had also agreed the UK’s first common file format, structure and wrapper to enable TV programme delivery by digital file. The guidelines complement the common standards for tape delivery of HD and SD TV programmes and endeavour to avoid a situation where a number of different file types and specifications proliferate. The inclusion of editorial and technical metadata creates a consistent set of information for the processing, review, and scheduling of programmes, as well as their onward archiving, sale and distribution across the television industry.
  