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Spec
https://html.spec.whatwg.org/multipage/embedded-content.html#dom-mediaerror-message
WHATWG HTML5 spec changed in [1].
W3C web-platform-tests includes test in [2].
TAG review process was skipped since this feature is included now in the WHATWG HTML5 spec.
Summary
The MediaError.message DOMString field provides, if available, any additional vendor-specific error message detail to assist web authors debugging media player errors. The format and content of the string is left to vendors. It is populated at the time of MediaError creation.
Motivation
Previously, the MediaError object only allows standardized exposure of a very small enumeration of error codes (https://www.w3.org/TR/html52/semantics-embedded-content.html#error-codes). Web authors have requested greater detail of errors, even if they are exposed in vendor-specific messages.
A common example is that MSE (Media Source Extensions) emits MEDIA_ERR_DECODE and MEDIA_ERR_SRC_NOT_SUPPORTED from a large variety of places in the spec, and differentiating the actual reason for the error is difficult at best. Services that deliver content via HTMLMediaElement (with or without MSE) and that encounter MediaError errors in the user agent frequently need more detail than just MediaError.code from the user agent to diagnose content, web app or user agent problems, especially when those errors are hard-to-reproduce.
Interoperability and Compatibility Risk
This field is additive, and format and content of message is implementation-specific, by design.
Firefox: Shipped
Edge: Public support. They responded positively to a request for input from W3C participants in [3], improving on their existing vendor-prefixed "MediaError.msExtendedCode".
Web developers: Strongly positive signals from YouTube and others at least at FOMS/Demuxed 2016.
Ongoing technical constraints
None
Will this feature be supported on all six Blink platforms (Windows, Mac, Linux, Chrome OS, Android, and Android WebView)?
Yes
OWP launch tracking bug
Link to entry on the feature dashboard
https://www.chromestatus.com/features/4996058069336064Requesting approval to ship?
Yes. CL is in review currently at https://codereview.chromium.org/2660003003/
message
API as-is in the spec.message
.