Hi On Fri, Nov 03, 2006 at 11:02:09AM -0800, Ralph Giles wrote:
Forgive the cross posting, this affects several projects.
and forgive me too for doing the same ... (if the disscusion is inappropriate for any of the lists just say so and i wont CC that one anymore ...)
On Fri, Nov 03, 2006 at 12:50:27AM -0800, Unga wrote:
Currently Theora video in Matroska is not supported by Mplayer. To enable the support Michael Niedermayer has made the following proposal sometime back: http://article.gmane.org/gmane.comp.video.mplayer.nut.devel/214
The proposal is that we add a recommendation to the ogg vorbis spec to just concatenate the headers when embedding in a container that needs to store them in a blob, and that readers skip leading and trailing data based on known packet lengths and magic strings.
As Michael says, this works, and is just the sort of hacky spec wrangling ogg is (in)famous for. :)
I guess my only comment is that this isn't particularly general. While vorbis has a fixed set of header packets with "easy" to determine lengths, it's possible to do a codec with external framing in mind where this wouldn't work. The theora spec, for example, allows additional application-defined header packets after the initial required three.
It also means a cross-encapsulator has to understand a codec's header packet format to put the data in an ogg stream, which is something many implementors have complained loudly about. Therefore I'd like to counterpropose something with explicit packet lengths, like matroska has, or the "packed header" format the vorbis and theora rtp drafts use.
ive looked at the rtp draft and as far as i understand it it concatenates the first 2 packets and omits all further ones " A Theora Packed Configuration is indicated with the payload type field set to 1. Of the three headers, defined in the Theora I specification [16], the identification and the setup will be packed together, the comment header is completely suppressed. It is up to the client to provide a minimal size comment header to the decoder if required by the implementation. " this definitly has my support, not that that would make any difference... :) comments, userdata, and other non essential data does not belong to a global codec specific header be it in rtp or any container normal containers have their own fields to store data like author, comment, user specified metadata and so on yes its a nightmare to convert from ogg to other containers or back but putting this data in the global codec specific header does not solve anything, the data would be as usefull as random data put there, and for rtp resources would be wasted to ensure error free delivery of possibly large and useless data [...] -- Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB In the past you could go to a library and read, borrow or copy any book Today you'd get arrested for mere telling someone where the library is