DRM Tools | Extensions | CDM

What is a PSSH and How to Extract It from an MPD File

📦 What is a PSSH in DRM?

PSSH stands for Protection System Specific Header, and it's a Base64-encoded data block included in MPEG-DASH (MPD) manifests. It is essential for initializing the DRM system (such as Widevine or PlayReady) and for requesting decryption keys from a license server.

🔍 What Does a PSSH Contain?

A Widevine PSSH contains a binary message (protobuf format) with the following fields:

✅ Version of the PSSH box (usually 0)
✅ System ID (UUID) that identifies the DRM system (e.g. Widevine = edef8ba9-79d6-4ace-a3c8-27dcd51d21ed)
✅ Content ID – usually identifies the video asset
✅ Key ID (KID) – the encryption key identifier
✅ Provider – name of the DRM provider or test label

🧪 PSSH Decoded Example

PSSH (Base64):
AAAAV3Bzc2gAAAAA7e+LqXnWSs6jyCfc1R0h7QAAADcIARIQ62dqu8s0Xpa7z2FmMPGj2hoNd2lkZXZpbmVfdGVzdCIQZmtqM2xqYVNkZmFsa3IzajIA

PSSH Box version: 0
SystemID (Widevine UUID): edef8ba9-79d6-4ace-a3c8-27dcd51d21ed

Decoded WidevinePsshData:
  - Crypto algorithm: Aesctr
  - Provider: widevine_test
  - Key ID: eb676abbcb345e96bbcf616630f1a3da
  - Content ID: 666b6a336c6a61536466616c6b72336a

Condensed format:
WidevinePSSH<Aesctr, key_id: eb676abbcb345e96bbcf616630f1a3da, content_id: "666b6a336c6a61536466616c6b72336a", provider: "widevine_test">

📄 Example: MPD with Embedded PSSH

Here’s a sample MPD file from Bitmovin Demo:

🔗 https://cdn.bitmovin.com/content/assets/art-of-motion_drm/mpds/11331.mpd

Inside the <Representation> section:

<ContentProtection schemeIdUri="urn:uuid:edef8ba9-79d6-4ace-a3c8-27dcd51d21ed">
  <cenc:pssh xmlns:cenc="urn:mpeg:cenc:2013">
    AAAAW3Bzc2gAAAAA7e+LqXnWSs6jyCfc1R0h7QAAADsIARIQ62dqu8s0Xpa7z2FmMPGj2hoNd2lkZXZpbmVfdGVzdCIQZmtqM2xqYVNkZmFsa3IzaioCSEQyAA==
  </cenc:pssh>
</ContentProtection>

🛠️ How to Extract the PSSH

Open the MPD in a browser or code editor
Search for the <ContentProtection> block with Widevine UUID
Copy the Base64 string inside the <cenc:pssh> tag
Use tools like:
- https://emarsden.github.io/pssh-box-wasm/
- mp4decrypt --show-pssh

🎯 Why PSSH Matters

It is required to request a license challenge
Sent to the Widevine License Server to get decryption keys
Used by tools like pywidevine, Shaka Packager, N_m3u8DL-RE

Understanding PSSH is essential when working with encrypted streaming content protected by DRM.

🔐 This is the starting point of any DRM decryption flow.

📚 Learn More: DRM Key Extraction Using Browser Extensions

For simple and fast decryption key extraction using your browser, check these beginner-friendly guides:

🔗 Widevine L3 Guessor 2025 – Extract DRM Keys Easily

🔗 WidevineProxy2 – Full DRM Extraction Proxy Extension

DRM Tools | Extensions | CDM