HDCP
High-bandwidth Digital Content Protection — encryption applied to the cable itself, between a video source and the screen it feeds. DRMDRMEncryption of the video file plus a licence server that issues a per-session key — so a downloaded copy stays unplayable.Open definition → protects the file up to the player; HDCP protects the last metre, where a capture card would otherwise sit and read a clean signal.
HDCP encrypts video on the HDMI or DisplayPort cable between a device and its screen, so a capture card wired in between records only scrambled data instead of a clean copy.
What is HDCP?
HDCP is a copy-protection layer for digital display connections, developed by Intel and licensed through Digital Content Protection LLC. It runs on HDMI, DisplayPort and DVI, and its job is narrow: keep the picture encrypted while it travels from a source to a screen.
The scope matters. HDCP knows nothing about your video file, your account rules or your licence server. It secures one hop — the physical link — and that is the hop where every other protection has already finished its work.
How the handshake works
Before any picture is sent, the source checks that the display holds valid HDCP keys. A device without them gets no signal, or a deliberately degraded one.
Both ends derive a session key and the video is encrypted with it for the whole connection. Unplugging and reconnecting starts the exchange again — which is why a switch flip can cause a two-second black screen.
An AV receiver or splitter in the middle is a repeater: it must authenticate downstream and report back what is attached. Devices that fail this are the single most common cause of HDCP errors in a home setup.
Sources carry revocation lists. A device whose keys were compromised and published can be refused by everything that receives an updated list.
Versions, and what 4K requires
| Version | Introduced | Typical ceiling | Status |
|---|---|---|---|
| HDCP 1.4 | 2009 | 1080p1080p (Full HD)Full HD at 1920×1080 — just over two million pixels. The default target for course, sales and web video.Open definition → over HDMI | Master key leaked in 2010; strippers exist |
| HDCP 2.2 | 2013 | 4K4K (2160p)Ultra HD at 3840×2160 — four times the pixels of Full HD, and the point where codec choice starts paying for itself.Open definition → and HDR | New cryptography plus locality checks |
| HDCP 2.3 | 2018 | 4K and above | Current; hardens the 2.x handshake |
Protected 4K content generally refuses to play over 1.4. This is why the same source can feed 1080p to an older television and go black at 4K.
Why HDCP errors happen
An HDCP error rarely means the content is broken. It means two devices could not agree on the link, and the chain is almost always at fault:
Inexpensive units often fail the repeater role. Connect the source directly to the display to confirm.
The source demands 2.2 for 4K, the display speaks 1.4. The fix is a lower resolutionResolutionThe pixel dimensions of a video frame — 480p, 720p, 1080p, 2160p (4K). Determines how sharp the picture looks on a given screen.Open definition → or newer hardware — there is no software workaround.
USB-C to HDMI adapters and docking stations vary in how they carry HDCP. Swapping the adapter is a faster test than swapping the display.
Recorders and streaming boxes in the chain are exactly what HDCP is designed to refuse. That is the system working, not failing.
HDCP and streaming DRM
For anyone delivering video rather than watching it, HDCP appears through a different door: as an output-protection requirement inside a DRMDRMEncryption of the video file plus a licence server that issues a per-session key — so a downloaded copy stays unplayable.Open definition → policy.
When a licence server issues a key it can attach conditions about the output. Studio-grade rules typically pair Widevine L1 — hardware-backed decryption — with HDCP 2.2 on the display link before releasing 1080p or 4K, and fall back to a lower rendition when either is missing. Both halves must hold: hardware decryption on the device, encryption on the cable.
For paid courses and corporate video, that strictness is usually more than the content needs. A policy that blackscreens a student because their laptop dock does not carry HDCP protects a file no studio licensed, and generates a support ticket that reads "your player is broken". Knowing the mechanism lets you set a resolution ceiling deliberately instead of inheriting a broadcaster's default.
What HDCP does not cover
| Threat | Covered? | What actually handles it |
|---|---|---|
| Capture card between device and screen | Yes | The link is encrypted end to end |
| Software screen recording | No | Happens before the display link — OS protections and watermarkingWatermarkingA mark burned into the frames. It prevents nothing — it makes a leaked copy point back at the account it came from.Open definition → |
| Downloading the stream | No | DRMDRMEncryption of the video file plus a licence server that issues a per-session key — so a downloaded copy stays unplayable.Open definition → encryption on the file itself |
| Replaying a harvested CDNCDN (Content Delivery Network)A global network of edge servers that caches video close to viewers, cutting latency and absorbing traffic spikes.Open definition → link | No | Signed URLsSigned URLA playback link carrying an expiry and a cryptographic token — it stops working once the window closes, and a tampered link never works.Open definition → with an expiry |
| A camera pointed at the screen | No | Nothing prevents it — watermarking makes it attributable |
Analogue capture is the honest boundary of every scheme in this family. HDCP closes the cable; it cannot close the room.
Further reading
- HDCP — Wikipedia — a vendor-neutral overview of the specification.
- DRM — how the licence exchange works.
- Multi-DRM — why Widevine and FairPlay run side by side.
- Watermarking — what covers screen recording.
- What is anti-piracy? — how the layers fit together.
- Video access control — domain, token and session rules.
