A synthesised IPv6 DNS answer does not prove the origin server is IPv6 native
DNS64 can synthesise AAAA data from IPv4 address data for use with an IPv6 to IPv4 translator. Keep client access and origin address support separate.
The journal
The viewing journal — page 62
Practical reading about streaming, devices and the decisions behind a better prepared setup.
A browser transferSize of zero does not always prove a cache hit
Resource Timing can hide cross origin size information. Interpret a zero transferSize with the applicable timing and CORS permissions before calling the request cached.
Finishing a media request is different from displaying its first frame
Resource Timing responseEnd measures the request endpoint in time. Decoding and presenting the media are separate observations.
A computer clock correction can distort a wall clock elapsed timer
Use a suitable monotonic clock for short browser operation durations. Keep wall time for dating the event and record sleep-related limits separately.
Counting browser callbacks is not a playback stopwatch
Media time updates and animation callbacks have different schedules. Use the appropriate timestamps or media position instead of assuming each callback represents a fixed duration.
Inspect the selected browser media resource rather than only the markup
currentSrc identifies the chosen media resource URL. It can help distinguish source selection from a filename copied out of page markup.