> On Jun 22, 2016, at 10:16 AM, Michael Bradshaw <mjbs...@gmail.com> wrote: > > On Tue, Jun 21, 2016 at 12:22 PM, Michael Niedermayer > <mich...@niedermayer.cc> wrote: >> what does "supported" / "unsupported" mean, is this defined somewhere ? > > As far as WebM is concerned, SegmentUID doesn't exist. > > In this situation, writing SegmentUID is Undefined-Ignore or > Optional-Fail/Forbidden, depending on the file. I concur with Dave's > analysis, but parsing may fail if SegmentUID is written and the master > element has an unknown size (which will be the case if ffmpeg is > writing to an unseakable output, like pipes). This is because master > elements with unknown size are terminated by the first unrecognized > would-be-child element[1], which would cause the parser to terminate > the Info element.
I don’t quite think that the EBML specification agrees with this explanation. See: "When EBML is used in transmission or streaming, data that is not part of an EBML Element is permitted to be present within a Master-element if `unknownsizeallowed` is enabled within that Master-element's definition. In this case, the reader should skip data until a valid Element ID of the same level or the next greater level of the Master-element is found. What Element IDs are considered valid within a Master-element is identified by the EBML Schema for that version of the EBML Document Type. Any data contained with a Master-element that is not part of an Element SHOULD be ignored." In this case a SegmentUID Element (undefined in webm) should be skipped be the reader rather than cause the termination of the reader. The end of an unknown-sized Element is determined by the beginning of the next known Element that is not a valid sub-element rather than the first unknown Element. > This would continue to screw up parsing, because now > there could be other children of Info (like DateUTC) after the > SegmentUID, and since the Info element has terminated and those aren't > valid children of Segment, it would cause the Segment element to > terminate. At that point, the file is pretty broken because now there > is no Segment element containing the Clusters and other elements. > > [1]: "The end of a Master-element with unknown size is determined by > the beginning of the next element that is not a valid sub-element of > that Master-element" (from the current EBML spec) Best Regards, Dave Rice _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
