ReadonlycontainerNull when the container never opened.
ReadonlytrackReadonlyvideoReadonlycodecNull on a video track the demuxer cannot name a codec for.
ReadonlycanNull where no decoder could be asked, which is every realm without
WebCodecs. Absent support is false, not null.
ReadonlytimingNull when no video track was reached.
ReadonlyremoteWhether the bytes come over a link, which is what makes a trailing index cost anything.
Everything the conditions are read from. Held as data so the reasoning is pure: the probe measures a source once and passes the facts in.