Common Media Client Data (CMCD) is a standard that enables media clients to communicate performance and playback metrics to media servers. This information helps servers monitor delivery using client-side metrics. The most important thing is that now client-side metrics are finally available on the server-side, which complement monitoring and help to optimize delivery.
Docs: Official CMCD specification PDF link. And a video explanation "What is CMCD" is on Youtube link.
The most common example of identifying user issues is measuring "response_time" from CDN logs. But this value often doesn't show the real picture:
- if the cache buffer is 2 seconds long, and the next chunk arrives with a 0.5 second delay, then...
- as you can imagine, nothing will happen on client-side at all. This is exactly what client metrics show.
This demo shows what exactly the player is sending to the server and how the server can respond to them. CMCD data is taked from the local player on the page!
Live demo is available here – https://codepen.io/apih9000/pen/XJWOYZW
Some interesting parameters to start from (full list you can see in the official documentation):
- bl (Buffer Length). Current buffer length of the media being played milliseconds. To detect how often buufer is emptied.
- br (Encoded Bitrate) Encoded bitrate of the current segment bits per second
- bs (Buffer State) Current state of the buffer enum (0 = stable, 1 = growing, 2 = shrinking)
- cid (Content ID) Unique identifier for the content being played string
- nrr (Next Request Range) Range of the next segment to be requested bytes
- ot (Object Type) Type of object being requested enum (v = video, a = audio, av = audio+video, etc)
- pr (Playback Rate) Current playback rate relative to normal speed ratio (1.0 = normal)
- sid (Session ID) Unique identifier for the playback session string
- su (Startup) Indicates if the request is for startup boolean
- tb (Throughput) Target bitrate for the next segment bits per second