[theora-dev] Can't find the setup code

Tabuleiro beta at tabuleiro.com
Mon Sep 16 07:11:57 PDT 2002

I have been working with the vp32 code for a couple of months, so I can try
to answer. Hope I am not wrong and I understood your question, but parsing
of the header and stream identification is probably not done at the codec
level. I think it is up to the VFW or QT playback engines, and they call the
codec to query its capabilities and ask for compressed/decompressed bags of
bytes in a format that was agreed upon during the codec initialization
phase. It is my understanding that data flow is more or less like this
during an AVI playback session:

1) AVI engine/libraries opens the file.
2) AVI engine parses the file, finds the video and audio streams
3) It finds a video stream with the vp31 FOURCC code, tries to find a
registered codec in the system to handle the stream
4) Now the codec is loaded by the AVI engine, which also queries the codecs
for its capabilities, request a given output format, etc.
5) The AVI engine starts passing compressed bags of bytes to the codec (with
some extra information to aid the decompression), and receives decompressed
data in response. Seeking in the stream is handled by the AVI engine.

I believe a similar sequence takes place during a compression sequence, so
the AVI engine (or the QT engine, depending on which codec you are building)
is actually the responsible for writing the final stream, including headers
and indexing information.

Not sure if this helps. How does it work in Ogg?

Mauricio Piacentini

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