Glossary
The vocabulary, in plain words
Every word here turns up somewhere in this site, in an app description, or in the message an app shows when something fails. Each one is defined once, properly, in the company of the words it belongs with.
Every term, A to Z
- 10-bit Video storing ten bits per colour channel instead of eight, for smoother gradients. In HEVC it is normal and well supported; in H.264 it is the single most common cause of a file that has sound but no picture on an iPhone.
- Adaptive bitrate Offering the same content at several quality levels and letting the player move between them as the connection changes. It is why streams degrade in sharpness rather than stopping.
- Anonymous analytics Counting events without recording who did them. The value of the claim depends entirely on what is attached to each event — and file names, paths and URLs are where such promises usually break.
- App group A shared container two apps from the same developer may both open — the only sanctioned crack in the sandbox. It is how a share extension hands a file to the app it belongs to.
- At rest vs in transit Encrypted at rest means unreadable on disk. Encrypted in transit means unreadable on the network. They are separate protections, and a product may honestly claim one while not doing the other.
- AV1 A royalty-free codec published in 2018, more efficient than HEVC and, unlike it, free of licensing disputes. Hardware decoding only arrived on Apple devices with the iPhone 15 Pro.
- Background transfer A download handed to the operating system so it continues after the app is closed. The system decides the timing, which is the trade for it continuing at all.
- Biometrics The device, not the app, confirms it is you; the app is told yes or no. No fingerprint or face data ever reaches an app, and none of it is a password.
- Bitrate How much data one second of video or audio uses, usually in megabits per second. It is the main thing that decides both file size and how much a device has to work.
- Buffering A player holding a few seconds of video ahead of what you are watching, so a brief network hiccup does not become a pause. When you see the word, the buffer has run out.
- Catch-up Watching something that has already been broadcast, by asking the provider's server for a past time on a channel. It only exists where the provider records; nothing is stored on your device.
- ChaCha20-Poly1305 A modern encryption algorithm that both hides data and detects tampering with it. Fast on phones, which do not always have hardware acceleration for the older alternative.
- Cloud storage Files kept on someone else's server, reached through that company's API — Dropbox, OneDrive, Box, pCloud. Each has its own interface, which is why apps support them one at a time.
- Codec The method used to compress a video or audio stream, and to decompress it again for playback. H.264, HEVC, AV1, AAC and MP3 are codecs. A codec is not a file format.
- Container The file structure that holds video, audio and subtitle tracks together and describes where each one is. MP4, MKV, AVI and WebM are containers. A container does not compress anything.
- Decoy vault A second passcode that opens a different, innocuous vault. Someone made to unlock the app can, and what opens is not the thing they were looking for.
- DRM Encryption that only licensed playback software can undo, using keys fetched from a licence server. FairPlay on Apple platforms, Widevine on Android and most web browsers.
- EPG The schedule: what is on each channel now, what is next, and what was on earlier. Delivered separately from the channels themselves, usually as an XMLTV file.
- H.264 The video codec that everything can decode. Published in 2003, still the safest choice for compatibility, and hardware-accelerated on every phone, computer and TV made in the last fifteen years.
- Hardware decoding Decoding video on a dedicated chip rather than the main processor. Far faster, far cooler and far kinder to a battery — but it only handles the codecs it was built for.
- HEVC H.264's successor, roughly half the size for the same quality. Every Apple device from 2015 onward decodes it in hardware, and it is what an iPhone records in.
- Hidden vs encrypted Hidden means an app agrees not to show something. Encrypted means the bytes on disk are unreadable without a key. The first is a promise; the second is arithmetic.
- HLS Apple's streaming protocol, and the one nearly everything uses. Video is cut into short segments listed in a text playlist, and the player fetches them in order over ordinary HTTP.
- IPTV Television delivered over the internet rather than over the air, by cable or by satellite. As a word it describes a delivery method and says nothing about who is entitled to deliver what.
- Key wrapping Encrypting the files with one key, and then encrypting that key separately with each way in. Changing a passcode rewraps a small key rather than re-encrypting everything.
- Keychain The system's protected store for small secrets, backed by the device's security hardware. It is where keys and tokens belong, and where nothing large should go.
- Keyframe A frame stored in full rather than as a difference from the frame before it. Seeking can only land on one, which is why a video sometimes jumps to a slightly different moment than you asked for.
- Local HTTP server An app answering web requests on your own network, so a web browser on your computer can open a page served by your phone. It is how Wi-Fi Transfer works, with no cable and no account.
- M3U playlist A plain-text list of channel names and stream addresses, and the most common way an IPTV subscription is delivered. It contains no video at all.
- Manifest The text file listing what a stream consists of. A master manifest lists the available quality levels; each of those points at a media manifest listing the actual segments.
- Parallel connections Splitting one file into ranges and fetching several at once. It helps when a single connection is being limited, and does nothing at all when the bottleneck is your own line.
- Range request Asking a server for a specific slice of a file — bytes 5,000,000 to 5,999,999 — instead of the whole thing. It is what makes a download resumable and what lets several connections fetch one file at once.
- Recovery code A one-time string that can unwrap the master key when the passcode is forgotten. Nobody can reissue it, because nobody else ever had it — including the people who wrote the app.
- Remux Moving the existing video and audio streams from one container into another without re-encoding them. Lossless, and fast enough to be limited by disk speed rather than by the processor.
- Resumable download A transfer that continues from exactly where it stopped rather than starting again, by recording how many bytes are committed and asking for the rest.
- Sandbox The rule that each app can only see its own storage. It is why one app cannot open another's downloads, and why "the file is next to the video" is not a thing that exists on iOS.
- Security-scoped bookmark A token that remembers permission to a folder outside the sandbox — an external drive, a folder in iCloud — so the app can reopen it later without asking again.
- Segment One short piece of a stream, typically two to ten seconds, delivered as its own file. An hour of video is hundreds to thousands of them.
- Transcode Decoding a stream and encoding it again, usually into a different codec or at a lower bitrate. Slow, and lossy every time — quality never comes back.
- WebDAV An extension to HTTP that turns a web server into a file server: list, read, write, move, delete. It is what Nextcloud and ownCloud speak, and what most NAS boxes offer.
- WebRTC A standard for connecting two devices directly, without a server between them once the connection exists. It is what device-to-device transfer uses to move a file across the room.
- Xtream Codes A panel software whose API became a de facto standard. Instead of a playlist file you get a server address, a username and a password, and the app asks the panel for channels, films, series and the guide.
- Zero-knowledge A design where the operator cannot read what it stores, because the keys never leave the user's devices. The test is simple: can they reset your password and still give you your data?
By subject
Video and codecs
Almost every confusing thing about video files comes from one distinction — between the box and what is in it. These are the words for both, and for the operations that move things between them.
11 termsStreaming and IPTV
Live television over the internet borrowed its vocabulary from three different places — broadcasting, the web, and one particular panel software that became a standard by accident. These are the words that come up.
11 termsFiles, downloads and transfer
Most of what feels arbitrary about files on an iPhone follows from one rule about isolation, and most of what makes downloads reliable follows from one feature of HTTP. These are both, plus the ways files get from one device to another.
11 termsPrivacy and encryption
These words get used loosely in app descriptions, and the differences between them are exactly where the value is. Hidden is not locked. Locked is not encrypted. And a key somebody else holds is not really yours.
10 terms