[theora-dev] More Q's about theora...

illiminable ogg at illiminable.com
Tue Apr 6 04:03:03 PDT 2004

I have a few more questions about theora... if someone could answer or point me to a source of the information...

Firstly in the header there is width and height parameters.

Are these fixed for the entire file ?

Is it possible for say halfway through the dimensions of the video to be changed ie two different size videos are spliced together ?

If it is... does the header represent the first size or the maximum size ?

Secondly what are the interleaving requirements...

Obviously it's much easier for the player if pages from the audio and video are interleaved relatively in sync... but is it legal to say have the entire video bitstream of the video, followed by the entire audio bitstream ?

Not that you probably want to go to that extreme... but is there a maximum defined amount that the video and audio can't be out of sync by ? ie can you go 10 seconds worth of video... 10 seconds worth of audio etc. Is the general consensus that it should be more than one page out of sync... ie a page of video which ends after the granule pos of the last page of audio... must be foloowed by pages of audio until the time of the audio exceeds the time of the last page of video etc.

Thirdly, what granule pos goes on a page that has no packets completing on it... ie a packet starts on page 1, runs all the way through page 2 and completes on page 3... what granule pos goes on page 2... the same as page 1 ?

Fourthly, must an uncompleted packet be continued on the next page ? ie can you have
Page 1... start of packet 1 of video
Page 2... some audio packets
Page 3... rest of packet 1of video... then some more.

Fifthly, does vorbis define meaning to granule pos... ie generally the granule rate of audio is the sample rate... ie page ending at 44100 in 44kHz stream is a stream time of 1 second... is this a requirement... should all players still be able to play if i say decide to multiply all granule pos's in the audio stream by 2... such that 88200 now represents 1 second in a 44kHz stream...

Thanks !

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