[gst-devel] addition of a buffer flag

Ronald Bultje rbultje at ronald.bitfreak.net
Wed May 12 07:11:09 CEST 2004


can't the mux rsimply extract this data from the packets directly? Note
that other codecs use the GstCaps property 'codec_data' for this. Matroska
treats Vorbis headers that way, too. The only notable exception to this
rule is really Ogg itself...

I'd say that a caps-property is cleaner.


On Wed, 12 May 2004, Thomas Vander Stichele wrote:

> Hi,
> for streaming purposes, we need a way for the network elements to know
> what part of the beginning of a data stream are to be considered
> "headers" and what is the raw data.  This isn't necessary for every
> format, but it is a requirement for Ogg.
> As an example, here's what needs to be done to stream Ogg/Theora+Vorbis.
> a) ogg page 1 contains a header for the vorbis stream
> b) ogg page 2 contains a header for the theora stream
> c) ogg page 3 contains two extra headers for the vorbis stream
> d) ogg page 4 contains two extra headers for the theora stream
> e) ogg page 5 is the first page containing data packets
> Every new client that picks up in the middle of the stream needs to
> first receive the first four ogg pages.  (Contrast with an mp3 stream,
> where you can pick in any time since each mp3 frame is preceded by a
> header, or with mpeg-video where the codec can choose to repeatedly send
> header info every few seconds).
> We discussed the various options.  We wanted to attach the information
> that some buffers represent a reusable header to the stream, instead of
> signalling it out-of-band through signals/deep_notify and property
> setting.
> So the choice is between events or buffer flags.  I prefer a buffer flag
> because it's the cleanest implementation:
> - the vorbis codec would generate the three packets of header info
> marked with this flag
> - same for theora
> - ogg muxer assembles pages with this flag
> - network streaming element looks at incoming flags, and puts all
> incoming buffers with this flag on an internal queue
> - every new connection to this element first receives the stored headers
> before picking in anywhere in the data stream.
> So, can I go ahead and add a _HEADER buffer flag for this ?
> Thomas
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