Common Media Client Data (CMCD) is a standard (CTA-5004) that allows video players to send real-time playback data to the CDN with every media request.
This data travels alongside the request itself, either as HTTP query parameters or headers, so no additional connection or reporting pipeline is required.
What Information CMCD Provides #
CMCD exposes client-side context that is normally invisible to the delivery layer, including:
- Buffer state – Current buffer length and starvation status.
- Bitrate and quality – Requested and encoded bitrate, as well as the top bitrate available in the manifest.
- Throughput – Measured and requested throughput as seen by the player.
- Object type and stream type – Manifest, audio, video, initialization segment, live vs. VOD.
- Session and content identifiers – Session ID and content ID for correlating requests belonging to the same playback session.
- Playback rate and deadline – Playback speed and the time until the requested object is needed for rendering.
How Flumotion Smart Multi CDN Uses CMCD #
Traffic Visibility #
Because CMCD data is attached to every request, Flumotion Smart Multi CDN can aggregate this information across playback sessions to provide visibility into real playback behavior by CDN provider and region.
This goes beyond standard access logs, which primarily describe the request and response themselves.
You can view these metrics on the Traffic Analytics page and investigate different types of media-related traffic behavior.
For example, you can:
- Analyze what percentage of clients receive segments at high, medium, or low bitrates.
- Identify video sessions that experience buffer starvation.
- Compare sessions affected by buffer starvation with sessions that do not experience it to help investigate possible causes.
Quality of Experience (QoE) Analysis #
Signals such as buffer starvation, requested vs. delivered bitrate, and bitrate stability allow Flumotion Smart Multi CDN to analyze actual viewer experience rather than delivery performance alone.
These signals can be correlated with specific CDN providers, edge locations, and networks (ASNs) to help identify where QoE degradation occurs.
This provides greater visibility into the playback quality experienced by end users.
How to Enable CMCD #
Flumotion Smart Multi CDN automatically collects CMCD data as long as the player sends it, either as part of the request query string or as request headers.
Many standard players, including dash.js, hls.js, and Shaka Player, as well as TV platforms and devices such as Roku, support CMCD.
However, in most cases CMCD is not enabled by default. You will need to enable CMCD in your player so that Flumotion Smart Multi CDN can use this information.
For more information, see Enable CMCD in Players.
CMCD Information Reported #
Flumotion Smart Multi CDN collects and presents the following information:
| Data | Description |
| Object Type | The media type delivered |
| Object Duration | The media object length in seconds |
| Stream Type | The stream type: VOD or live streaming |
| Streaming Format | The streaming protocol: HLS, DASH, etc. |
| Buffer Length | The player’s buffer length; longer is better |
| Buffer Starvation | Playback delays caused by buffer starvation; false indicates no buffer starvation |
| Startup Delay | Playback delays caused by initial buffering or seeking; false indicates no startup delay |
| Deadline | Time until a requested object is needed to avoid playback delays; longer is better |
| Requested Throughput | The throughput requested by the player for optimal playback |
| Measured Throughput | The throughput actually measured by the player |
| Top Bitrate | The bitrate required for optimal playback based on the current codec, sizing, and related parameters |
| Encoded Bitrate | The bitrate actually delivered to the player |