[gst-devel] [Fwd: GstIndex: some questions about usage]

Erik Walthinsen omega at temple-baptist.com
Wed Nov 22 04:05:47 CET 2006

Not sure why there's been a rash of people sending these questions directly 
to me all of the sudden...  Maybe the lists need to be more prominently 
placed in e.g. AUTHORS etc.

-------- Original Message --------
Subject: GstIndex: some questions about usage
From: Sebastian Dröge <slomo at circular-chaos.org>
To: Erik Walthinsen <omega at temple-baptist.com>
Date: Tue, 21 Nov 2006 17:06:31 +0100

I'm currently trying to understand GstIndex in all it's aspects and
you're the original author judging from the header. I have some open
questions that I couldn't answer myself from reading the code:

a) What exactly is a "group" meant to be? What would be example usages
where someone would use different groups? I saw that you can give a
group a certainty and a parent group with more certainty but these
informations are never used in the implementations GstMemIndex and
GstFileIndex and are in the private API part of the group. On the other
hand there are functions to set/get the certainty of the index, how
would this be useful?

b) What's exactly the usecase of different writer ids? What advantage
could one have when using different writer ids instead of a single one
for everything? Also why is there a gst_index_add_id() to add a writer
id to the index when one should always get the writer id via

c) Is it correct that associations have to be added in chronological
order? GstMemIndex prepends them to a list where one of the previous (or
next) elements of the list is used when the parameters of the found
entry are not the ones that is requested. If the list is ordered
randomly the previous (or next) matching element could be something
completely different to the one you want

d) What exactly is the use of entries with type GST_INDEX_ENTRY_OBJECT,
i.e. gst_index_add_object()?

That's it for now... I hope you find some time to answer my questions :)
I plan to either convert all demuxers/muxers/parsers to GstIndex instead
of home-grown implementations or or write a new class that better fits
the requirements of all elements.


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