How does page speed collect LCP value when there is no timing-allow-origin?

[xiaofud]

If the image resource has no timing-allow-origin header, will the LCP value be the loadTime or does page speed have its way to get renderTime?

[tunetheweb]

No we only have the loadTime, which can lead to some issues like #369 (comment)

[tunetheweb]

Note that the Chrome User Experience Report (CrUX) does not have this constraint and so the CrUX data surfaced in tools like PageSpeed Insights will have the correct LCP time.

This is one difference between CrUX and RUM (including web-vital.js): https://web.dev/crux-and-rum-differences/#cross-origin-resources

[xiaofud]

Note that the Chrome User Experience Report (CrUX) does not have this constraint and so the CrUX data surfaced in tools like PageSpeed Insights will have the correct LCP time.

This is one difference between CrUX and RUM (including web-vital.js): https://web.dev/crux-and-rum-differences/#cross-origin-resources

Thanks! The page you provided is helpful.