Hi On Sat, Nov 04, 2006 at 07:09:23AM +1100, Silvia Pfeiffer wrote:
Let me see if I understand the problem correctly.
Matroska provides only one header packet per codec to identify it.
my proposal was about the 2 or 3 codec initalization packets at the start of vorbis, theora, ... streams identifying the codecs is not a problem in any container format besides ogg i know of, containers simply have some field which identifies the codec, that can be a 32bit or 16bit integer, or a variable length string, or in case of matroska several redundant systems the problem with the initalization packets, or super keyframes or sequence headers or whetever you want to call them is that there are several of them but containers are generally designed to handle just one such packet per stream if you would simply store these 3 packets like normal packets then a demuxer which is told by the user to seek to lets say 5min into the stream will do so, first it will pass the single global header (this one is empty in our example) to the codec next it would search for a keyframe around the requested 5min and start passing packets begining with the keyframe to the decoder which would fail as it never received the 3 initalization packets ... if now the 2 or 3 packets are merged into one and stored in the appropriate spot for the global packet for the stream then everything will work fine, of course that requires that the decoder is able to parse or the demuxer is able to split the merged packet (for that a few words in the relevant specs would be helpfull, whatever the exact method is which is used to merge the packets ...) also note this is not about matroska alone, but rather many containers avi, wav, nut, matroska, nuv, asf to name the ones which IIRC support a single global header but do not really support multiple ones without codec specific hacks ... mpeg-ps/ts does not support any global header, they expect such headers to be repeated before keyframes (mpeg1/2 video does exactly that with their sequence headers) mov allows everything but tends to need a special case per codec in the demuxer also APIs tend to support passing a single global packet around but tend not to support multiple ones ... [...]
I am not sure if Matroska would encapsulate the clean codec stream or an ogg framed stream. I also don't understand if there would be one blob per codec in the case of a multitrack file (e.g. Theora + Vorbis) or whether there would be just one large, interleaved blob. In any case, I might put our experience into the mix to get this right.
putting a container into a container is the most insane thing you could do, it also isnt allowed in many containers, avi requires each packet to be a single packet (people do ignore this yes i know but they generally dont put other containers in avi), nut explicitly says that containers inside streams render the file invalid and any player playing such a file is not nut compliant, i dont know about matroska but it would surprise me if a vorbis+theora in ogg stream could be put in matroska without violating some rules also what is such a stream audio? video? something else? also ignoring the rules, such files are a nightmare to support, and even if supported will have a lot of random problems with AV sync [...] -- 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