Now that you have decided which sources you need for your project, it's time to know them better! Don't forget you may always need audio tracks from different sources than the one used for video, so sometime audio only ones could be necessary, or you want to add different subtitles.
Audio/video sources
Digital Cinema: the best quality source for a movie; 4K and 2K quality; I think it's impossible to find out an untouched source; *maybe* few titles at reduced quality (but still better than BD) are leaked out of the theaters.
UHD-BD: 4K (actually, UltraHD) quality, HDR, 10bit color depth, lossless high quality audio tracks; actually, one of the best sources available, along with few web sources; still strongly copy protected, it's possibly however to capture its video using high quality capture card, preserving most of its original quality.
BD, DVD: if you have not the needed ones, you could buy them almost everywhere - in a shop, online, new and used; my advice is to buy it used if you can, but be aware that sometimes used BD/DVD could be so hard scratched that will be impossible to extract tracks from them! There are a lot of software that are able to decrypt and extract the tracks, but we'll not talk about them because it's beyond the scope of this article.
HD-DVD: as far as I know, it's impossible to buy them brand new, unless a little store has still some of them... but they are quite easy to find used online. There are few software capable of decrypt and extract the tracks, so you should find a working one before considering getting a disc AND a player - remember, you will need a proper HD-DVD or multi player, as the normal BD or DVD player could not read HD-DVD discs!
D-Theater: quite rare, they have a very good audio and video quality; you need a D-VHS player, and some kind of hardware and software to extract the tracks bit-perfect - of you could always try to capture them via the player's analog outputs.
Other digital sources on physical support: as UMD titles are all available on other formats (so no worries about them), the only ones I could think of are VCD and eventually SVCD and CBHD; they are really widespread in Asia, and sometimes the only way to find out a specifical title in digital form; obtainable online, their tracks are quite easy to extact.
Film: 70mm and 35mm are the ones used in theaters, and usually not commercially available for the general public; it's still possible to find some titles in collectors' hands, and they could be captured using pricey projectors and some kind of hardware; difficult to find and capture, the quality could range from spectacular to ugly, depending from several factors - film stock used, generation print, status; in the best cases, it could be way better than BD. 16mm and 8mm were available for sale; quality varies as well the cinema films, but it's lower and maybe the best ones could be comparable with DVD.
LD: the best analog format, the last one produced at the very beginning of this century... more than 50,000 titles available, could be found used - and sometimes new - quite easily online; many times it's the only way to find a specific video version, or different audio mix, commentary, soundtrack; you need a laserdisc player, and a capture device, to transform analog video to digital; it's possible to capture digital audio tracks bit-perfect, in all their formats - PCM, AC3, DTS
VHS: the last resource; difficult to find new, used tapes could be warn and/or have drop outs (very probable) that will ruin the capture; you need a VHS or S-VHS player, and a capture device; a TBC is not mandatory, but strongly adviced - you can also use DVD recorders as pass-through, as almost (if not) all of them have a good TBC.
Other analog sources on physical support: S-VHS titles are very few, and they should be all available on other formats; VHD and CED are old analog disc format, and they need related player and a capture device; there are some titles still not available on other formats, though; don't forget MUSE laserdisc, the only analog HD disc format!
Digital streaming: usually crypted in some way, to avoid unauthorized copy, maybe it could be decrypted using some software, or it's still possible to capture it via analog; as today, quality is way lower than their physical counterparts (BD for HD material, DVD for SD material) but sometimes the only way to obtain a given version or title.
Digital broadcasting: aerial, cable or satellite TV transmissions, they could be captured in digital way, usually bit-perfect, using a software or some kind of hardware connected to the proper decoder, like a S-VHS recorder. Quality varies, depending on several factors; often it is possible to find different version of a given title, or a title still not available in other formats, or that it will never be in the future.
Analog broadcasting: aerial, cable or satellite TV transmissions, today not available anymore in many parts of the world; it could be recorded in digital way - PC, DVD recorder - or analog way - W-VHS, S-VHS, VHS, Betamax; usually it's the latest source to be searched, but sometimes it's possible to find out some real gems, for example MUSE analog HD material recorded on D-VHS or W-VHS
Audio-only sources
Cinema DTS: CD-ROMs containing theatrical audio tracks; not commercially available, sometimes they were scrapped by the theaters, so it's still possible to find them for sale online, but they are quite rare; quality is very high, similar to home version DTS tracks; often they have different mixes.
DVD-Audio, SACD: the quality is very high, could be multichannel, and on par with DTS-HD MA or Dolby TrueHD; the tracks could be extracted bit-perfect.
CD: usually they are standard CDDA, but could be HDCD, or even DTS-CD - multichannel compressed!
Vynil records: despite the fact it's analog, it could have a very high quality, that could rival or even surpass CDDA, depending very much by the turntable, pickups, styluses and capture device.
Tapes: lowest quality of all, depending on eventual noise reduction applied, tape player and capture device; maybe some soundtracks are still not available on other formats, but I think it's hardly the case.
Other commercially released: DCC, MiniDisc, DAT and some other discontinued format may contain soundtracks not available on other format.
Radio broadcasting/bootleg: quality depends on hardware (radio, cables, recorder, microphone) and software (tape, computer program) used; it could be the only way to find some rare and obscure material.
Subtitles sources
Digital audio/video formats: usually it's possible to extract subtitles tracks in graphical or text form.
Analog audio/video formats: it's quite hard, but still possible, to extract Closed Caption and/or Teletext from analog formats, using some kind of hardware decoders and/or computer software.
Text files: sometimes there are no commercially available subtitles, so fans make them on their own; be aware, because often they contains errors, due to wrong translation.
Written text: in rare cases, it's possible to find partial or complete dialog transcriptions on books or magazines.
In the next steps, we'll see where to find these sources.
Audio/video sources
Digital Cinema: the best quality source for a movie; 4K and 2K quality; I think it's impossible to find out an untouched source; *maybe* few titles at reduced quality (but still better than BD) are leaked out of the theaters.
UHD-BD: 4K (actually, UltraHD) quality, HDR, 10bit color depth, lossless high quality audio tracks; actually, one of the best sources available, along with few web sources; still strongly copy protected, it's possibly however to capture its video using high quality capture card, preserving most of its original quality.
BD, DVD: if you have not the needed ones, you could buy them almost everywhere - in a shop, online, new and used; my advice is to buy it used if you can, but be aware that sometimes used BD/DVD could be so hard scratched that will be impossible to extract tracks from them! There are a lot of software that are able to decrypt and extract the tracks, but we'll not talk about them because it's beyond the scope of this article.
HD-DVD: as far as I know, it's impossible to buy them brand new, unless a little store has still some of them... but they are quite easy to find used online. There are few software capable of decrypt and extract the tracks, so you should find a working one before considering getting a disc AND a player - remember, you will need a proper HD-DVD or multi player, as the normal BD or DVD player could not read HD-DVD discs!
D-Theater: quite rare, they have a very good audio and video quality; you need a D-VHS player, and some kind of hardware and software to extract the tracks bit-perfect - of you could always try to capture them via the player's analog outputs.
Other digital sources on physical support: as UMD titles are all available on other formats (so no worries about them), the only ones I could think of are VCD and eventually SVCD and CBHD; they are really widespread in Asia, and sometimes the only way to find out a specifical title in digital form; obtainable online, their tracks are quite easy to extact.
Film: 70mm and 35mm are the ones used in theaters, and usually not commercially available for the general public; it's still possible to find some titles in collectors' hands, and they could be captured using pricey projectors and some kind of hardware; difficult to find and capture, the quality could range from spectacular to ugly, depending from several factors - film stock used, generation print, status; in the best cases, it could be way better than BD. 16mm and 8mm were available for sale; quality varies as well the cinema films, but it's lower and maybe the best ones could be comparable with DVD.
LD: the best analog format, the last one produced at the very beginning of this century... more than 50,000 titles available, could be found used - and sometimes new - quite easily online; many times it's the only way to find a specific video version, or different audio mix, commentary, soundtrack; you need a laserdisc player, and a capture device, to transform analog video to digital; it's possible to capture digital audio tracks bit-perfect, in all their formats - PCM, AC3, DTS
VHS: the last resource; difficult to find new, used tapes could be warn and/or have drop outs (very probable) that will ruin the capture; you need a VHS or S-VHS player, and a capture device; a TBC is not mandatory, but strongly adviced - you can also use DVD recorders as pass-through, as almost (if not) all of them have a good TBC.
Other analog sources on physical support: S-VHS titles are very few, and they should be all available on other formats; VHD and CED are old analog disc format, and they need related player and a capture device; there are some titles still not available on other formats, though; don't forget MUSE laserdisc, the only analog HD disc format!
Digital streaming: usually crypted in some way, to avoid unauthorized copy, maybe it could be decrypted using some software, or it's still possible to capture it via analog; as today, quality is way lower than their physical counterparts (BD for HD material, DVD for SD material) but sometimes the only way to obtain a given version or title.
Digital broadcasting: aerial, cable or satellite TV transmissions, they could be captured in digital way, usually bit-perfect, using a software or some kind of hardware connected to the proper decoder, like a S-VHS recorder. Quality varies, depending on several factors; often it is possible to find different version of a given title, or a title still not available in other formats, or that it will never be in the future.
Analog broadcasting: aerial, cable or satellite TV transmissions, today not available anymore in many parts of the world; it could be recorded in digital way - PC, DVD recorder - or analog way - W-VHS, S-VHS, VHS, Betamax; usually it's the latest source to be searched, but sometimes it's possible to find out some real gems, for example MUSE analog HD material recorded on D-VHS or W-VHS
Audio-only sources
Cinema DTS: CD-ROMs containing theatrical audio tracks; not commercially available, sometimes they were scrapped by the theaters, so it's still possible to find them for sale online, but they are quite rare; quality is very high, similar to home version DTS tracks; often they have different mixes.
DVD-Audio, SACD: the quality is very high, could be multichannel, and on par with DTS-HD MA or Dolby TrueHD; the tracks could be extracted bit-perfect.
CD: usually they are standard CDDA, but could be HDCD, or even DTS-CD - multichannel compressed!
Vynil records: despite the fact it's analog, it could have a very high quality, that could rival or even surpass CDDA, depending very much by the turntable, pickups, styluses and capture device.
Tapes: lowest quality of all, depending on eventual noise reduction applied, tape player and capture device; maybe some soundtracks are still not available on other formats, but I think it's hardly the case.
Other commercially released: DCC, MiniDisc, DAT and some other discontinued format may contain soundtracks not available on other format.
Radio broadcasting/bootleg: quality depends on hardware (radio, cables, recorder, microphone) and software (tape, computer program) used; it could be the only way to find some rare and obscure material.
Subtitles sources
Digital audio/video formats: usually it's possible to extract subtitles tracks in graphical or text form.
Analog audio/video formats: it's quite hard, but still possible, to extract Closed Caption and/or Teletext from analog formats, using some kind of hardware decoders and/or computer software.
Text files: sometimes there are no commercially available subtitles, so fans make them on their own; be aware, because often they contains errors, due to wrong translation.
Written text: in rare cases, it's possible to find partial or complete dialog transcriptions on books or magazines.
In the next steps, we'll see where to find these sources.