29-09-2021, 06:29 PM
(This post was last modified: 29-09-2021, 06:39 PM by Mike Watterson.)
Just off the top of my head.
All video is originated as a raster, horizontal, then vertical. It's displayed that way too.
https://en.wikipedia.org/wiki/Display_resolution
Compression uses blocks.
Interlacing is a cunning analogue compression by 50%. It makes the digital compression, or resolution /frame rate conversion hard, so actually most systems convert interlaced to progressive. Film scanning is progressive, unlike pointing an interlaced camera at a screen, so that can be detected to make unravelling the interlacing easier. The film progressive 24 fps to "NTSC" (at any interlaced resolution), really 30 fps 60Hz is particularly nasty. So USA has a sort of fake HD that is 640 x 480 progressive, only on digital broadcasts.
Before HDMI digital in Europe, the USA had semi-HD via component video from DVDs (as ones from film for the USA are stored at 480 lines progressive 24 fps and converted to 30 fps interlaced on playback in the DVD player. These signals could be up to 1440 x 480 progressive 60 fps or later in Europe 1440 x 576 progressive 50 fps (simply doubling frames with interpolation and playing the 48 fps at 50 fps). PAL DVDs from movies are ALSO 24 fps but 576 lines. They are played at 25 fps interlaced so the sound track is usually pitch changed by 24/25th before digital DVD encoding.
The basic broadcast digital signals were originally much like DVDs. An MPEG2 compression (using blocks of video). Sound had more types of compression. Satellite (DVB-S, now also DVB-S2), Cable (DVB-C), USA Digital Terrestrial (ATSC) and most other Terrestrial systems (DVB-T) use different modulation schemes. Satellite originally uses QPSK for digital, Cable uses a single carrier 256 to 2048 QAM and European Digital TV, DVB-T (and most others not USA or China related) uses a variation of the DAB scheme, thousands of separate QAM carriers.
Multiple channels are serialised using the MPEG2 Transport stream. This is not the SAME MPEG2 as the compression. Digital internet data on Satellite or cable also uses MPEG2 transport streams. Then a frame based FEC (Forward Error Correction) is used. Satellite might have FEC 2/3 to allow a smaller dish or less power. A feed using big professional dishes might be 7/8 to save bandwidth, or have more quality.
The Luminance needs more data than the B-Y and R-Y signals, so you'll see things like 4:2:2 mentioned. "PAL" and "NTSC" origin video use different chroma sampling rules.
Then they added more frame rates, more resolutions (even 544 x 576 instead of 720 x 576, even on widescreen) to save bandwidth. Full 1920 x 1080 (at whatever frame rate) is now rarer. The 1440 x 1080 is more common, especially on terrestrial.
Bean counters realised they could choose the compression. More compression means waving grass looks smooth, panning looks badly frame rate converted etc. So many "cheaper" channels used 544 x 576 (480 in USA )or 1440 x 1080 and more compression. Lower transmission charges. To the extent that a good 720 x 576 (or 480) DVD could be upscaled and fed by HDMI to a 1920 x 1080 WS TV and look better than broadcast "HD". Some channels even use 1/4 NTSC or 1/4 PAL resolution.
All HD is now MPEG4. Countries that started Digital TV later (Ireland) use the MPEG4 for SD. It's not for better quality but to save even more bandwidth. Then the same MPEG transport stream can have more channels. You see the same with DAB. The DAB rates reduced to fit in more channels. Almost no-one uses DAB+ for better quality, but to fit twice as many channels. Due to lack of spectrum (sell off to Mobile) the UK and some other places put the HD Terrestrial on DVB-T2 modulation. Ireland has less channels and ALL are MPEG4, even SD, so Ireland uses the original DVB-T.
The 2K TV is usually 2560 x 1440, versus HD (now FHD) of 1920 x1080. Almost any display resolution is called HD Ready if it can downsample 1920 x 1080, and now HD if 720, 768 or 800 lines. The 4K is about 3840 × 2160. However movies, scanning film and Broadcast TV can all mean slightly different things by 2K and 4K.
Any digital format from analogue film by scanning should use twice the horizontal and vertical resolution, in progressive format of the target video. Then the file is digitally anti-aliased before final MPE2 or MPEG4 compression. Sadly to save money Blu-Ray might use the 1440 x 1152 or 2048 x 1152 master scan and resample it to 1920 x 1080 instead of a fresh 3840 x 2160 scan. Some 4K streaming and Satellite content may just be 4K film scans for mastering Blu Ray. A Digital 4K camera naturally is 4K.
So DVDs made from scanned film will upsample to 1920 x 1080 (HD) far better than SD digital camera content, unless it's a HD 3 chip camera used for SD.
Very early non-linear editing systems, practically before DVDs existed, used Motion JPEG compression. It's still a better format to edit than MPEG2 or MPEG4 because every frame is real. I had one in the 1990s and 800 Mbyte HDD was about 15 minutes. MPEG uses key frames and stores only changes between them. So a rubbish format to edit. It's also why test cards for digital broadcast links to show there is a signal have moving element.
There were video CDs before DVDs. Only 1/4 PAL or NTSC resolution, so a VHS had twice the lines! An early version was CDi. Early CDi and VCD had poorish MPEG2 compression. I have two Star Trek films, a CDI and VCD. By 2000 my one VCDs were better. I still have the giant ISA card in the attic with MJPEG hardware and HW video overlay for VGA loop through and real PAL capture and output. Adobe Premiere on Windows For Workgroups 3.11 for editing.
All video is originated as a raster, horizontal, then vertical. It's displayed that way too.
https://en.wikipedia.org/wiki/Display_resolution
Compression uses blocks.
Interlacing is a cunning analogue compression by 50%. It makes the digital compression, or resolution /frame rate conversion hard, so actually most systems convert interlaced to progressive. Film scanning is progressive, unlike pointing an interlaced camera at a screen, so that can be detected to make unravelling the interlacing easier. The film progressive 24 fps to "NTSC" (at any interlaced resolution), really 30 fps 60Hz is particularly nasty. So USA has a sort of fake HD that is 640 x 480 progressive, only on digital broadcasts.
Before HDMI digital in Europe, the USA had semi-HD via component video from DVDs (as ones from film for the USA are stored at 480 lines progressive 24 fps and converted to 30 fps interlaced on playback in the DVD player. These signals could be up to 1440 x 480 progressive 60 fps or later in Europe 1440 x 576 progressive 50 fps (simply doubling frames with interpolation and playing the 48 fps at 50 fps). PAL DVDs from movies are ALSO 24 fps but 576 lines. They are played at 25 fps interlaced so the sound track is usually pitch changed by 24/25th before digital DVD encoding.
The basic broadcast digital signals were originally much like DVDs. An MPEG2 compression (using blocks of video). Sound had more types of compression. Satellite (DVB-S, now also DVB-S2), Cable (DVB-C), USA Digital Terrestrial (ATSC) and most other Terrestrial systems (DVB-T) use different modulation schemes. Satellite originally uses QPSK for digital, Cable uses a single carrier 256 to 2048 QAM and European Digital TV, DVB-T (and most others not USA or China related) uses a variation of the DAB scheme, thousands of separate QAM carriers.
Multiple channels are serialised using the MPEG2 Transport stream. This is not the SAME MPEG2 as the compression. Digital internet data on Satellite or cable also uses MPEG2 transport streams. Then a frame based FEC (Forward Error Correction) is used. Satellite might have FEC 2/3 to allow a smaller dish or less power. A feed using big professional dishes might be 7/8 to save bandwidth, or have more quality.
The Luminance needs more data than the B-Y and R-Y signals, so you'll see things like 4:2:2 mentioned. "PAL" and "NTSC" origin video use different chroma sampling rules.
Then they added more frame rates, more resolutions (even 544 x 576 instead of 720 x 576, even on widescreen) to save bandwidth. Full 1920 x 1080 (at whatever frame rate) is now rarer. The 1440 x 1080 is more common, especially on terrestrial.
Bean counters realised they could choose the compression. More compression means waving grass looks smooth, panning looks badly frame rate converted etc. So many "cheaper" channels used 544 x 576 (480 in USA )or 1440 x 1080 and more compression. Lower transmission charges. To the extent that a good 720 x 576 (or 480) DVD could be upscaled and fed by HDMI to a 1920 x 1080 WS TV and look better than broadcast "HD". Some channels even use 1/4 NTSC or 1/4 PAL resolution.
All HD is now MPEG4. Countries that started Digital TV later (Ireland) use the MPEG4 for SD. It's not for better quality but to save even more bandwidth. Then the same MPEG transport stream can have more channels. You see the same with DAB. The DAB rates reduced to fit in more channels. Almost no-one uses DAB+ for better quality, but to fit twice as many channels. Due to lack of spectrum (sell off to Mobile) the UK and some other places put the HD Terrestrial on DVB-T2 modulation. Ireland has less channels and ALL are MPEG4, even SD, so Ireland uses the original DVB-T.
The 2K TV is usually 2560 x 1440, versus HD (now FHD) of 1920 x1080. Almost any display resolution is called HD Ready if it can downsample 1920 x 1080, and now HD if 720, 768 or 800 lines. The 4K is about 3840 × 2160. However movies, scanning film and Broadcast TV can all mean slightly different things by 2K and 4K.
Any digital format from analogue film by scanning should use twice the horizontal and vertical resolution, in progressive format of the target video. Then the file is digitally anti-aliased before final MPE2 or MPEG4 compression. Sadly to save money Blu-Ray might use the 1440 x 1152 or 2048 x 1152 master scan and resample it to 1920 x 1080 instead of a fresh 3840 x 2160 scan. Some 4K streaming and Satellite content may just be 4K film scans for mastering Blu Ray. A Digital 4K camera naturally is 4K.
So DVDs made from scanned film will upsample to 1920 x 1080 (HD) far better than SD digital camera content, unless it's a HD 3 chip camera used for SD.
Very early non-linear editing systems, practically before DVDs existed, used Motion JPEG compression. It's still a better format to edit than MPEG2 or MPEG4 because every frame is real. I had one in the 1990s and 800 Mbyte HDD was about 15 minutes. MPEG uses key frames and stores only changes between them. So a rubbish format to edit. It's also why test cards for digital broadcast links to show there is a signal have moving element.
There were video CDs before DVDs. Only 1/4 PAL or NTSC resolution, so a VHS had twice the lines! An early version was CDi. Early CDi and VCD had poorish MPEG2 compression. I have two Star Trek films, a CDI and VCD. By 2000 my one VCDs were better. I still have the giant ISA card in the attic with MJPEG hardware and HW video overlay for VGA loop through and real PAL capture and output. Adobe Premiere on Windows For Workgroups 3.11 for editing.
