- From: David Singer <singer@apple.com>
- Date: Fri, 09 Dec 2016 10:32:26 -0800
- To: David Evans via GitHub <sysbot+gh@w3.org>
- Cc: public-html-media@w3.org
I agree the presence of a brand that you support gives you permission to decode a file and ignore what you don’t understand. The spec. should admit the possibility of the existence of boxes that can be ignored. > On Dec 9, 2016, at 6:31 , David Evans via GitHub <sysbot+gh@w3.org> wrote: > > bbcrddave has just created a new issue for > https://github.com/w3c/media-source: > > == Allow non-ISO/IEC14496-12 top-level boxes in ISOBMFF Byte Streams > == > The [Segment Parser > Loop](https://w3c.github.io/media-source/index.html#sourcebuffer-segment-parser-loop) > states the following: > > "If the input buffer contains bytes that violate the SourceBuffer byte > stream format specification, then run the append error algorithm and > abort this algorithm." > > The [ISO BMFF Byte Stream > Format](https://www.w3.org/TR/mse-byte-stream-format-isobmff/) states: > "Valid top-level boxes defined in ISO/IEC 14496-12 other than ftyp, > moov, styp, moof, and mdat are allowed to appear between the end of an > initialization segment or media segment and before the beginning of a > new media segment. These boxes MUST be accepted and ignored by the > user agent and are not considered part of the media segment in this > specification. " > > This appears to imply only valid top-level boxes defined in 14496-12 > are allowed to appear in a stream, and that strictly compliant > implementations should reject input buffers containing any other > top-level boxes. > > MPEG-DASH (ISO/IEC 23009-1:2014) specifies a new box (`emsg`) as a > mechanism for signalling both generic in-band metadata related to the > media and DASH-specific operations. It further constrains this new box > to be placed before the `moof` - i.e. at the top level. > > It seems that the byte stream format specification needs either to be > less strict in general in terms of extensions, or include references > other than 14496-12 in the list. > > Note: at least one implementation has already included `emsg` in its > list of valid top-level boxes [1]. > > See also: > 1. https://bugs.chromium.org/p/chromium/issues/detail?id=276303 > 2. https://bugzilla.mozilla.org/show_bug.cgi?id=1322587 > > > Please view or discuss this issue at > https://github.com/w3c/media-source/issues/174 using your GitHub > account > David Singer Manager, Software Standards, Apple Inc.
Received on Friday, 9 December 2016 18:32:55 UTC