[theora] Indexing Ogg files for faster seeking

[Silvia Pfeiffer]

Hi Chris,

I love the idea and even more that you already have working code.

I think this is probably the cleanest approach to Ogg seeking that I
have seen in a while. I think the additional overhead is tolerable.

Please note that there will be a third solution to the problem of
seeking over HTTP which will not require Ogg files with keyframe index
tracks, but can make use of them. The idea here is to use media
fragment URIs to address into a media file and retrieve the relevant
byte ranges. This is based on communicating it to the server and the
server then composing together the relevant byte ranges as a reply. If
the file on the server had your keyframe index track, it could
probably identify the right byte range faster, so that's a good thing.

I think this is awesome and should be added to the Xiph wiki. Also, it
should go into ffmpeg2theora, IMHO, but of course that's up to others
to decide.

Cheers,
Silvia.


On Tue, Sep 22, 2009 at 1:27 PM, Chris Pearce <chris at pearce.org.nz> wrote:
> I've developed an indexer which embeds a keyframe index track in Ogg
> files. It embeds the index in its own track, so that players that don't
> understand or don't want to use the index can just ignore it.
>
> Ogg needs this to make seeking over networks faster and more efficient.
>
> Currently we must do a bisection search when seeking, which usually
> takes aound 6 HTTP requests, give or take a few. If we are to compete
> with existing internet video (AKA the "YouTube" case) we need to do that
> faster and more efficiently - using fewer HTTP requests. We need an
> index so that seeking only takes 1 HTTP request.
>
> Using an index of keyframes also makes it easier to seek without visual
> artifacts - though of course robust players should be able to do that in
> the absence of an index.
>
> You can download the source code for my indexer here:
> http://github.com/cpearce/OggIndex
>
> My specification for the index track is stored in that repo, here:
> http://tinyurl.com/l4c9yg
>
> I'd appreciate comments on the spec...
>
> To see how it improves network seeking performance, you can download a
> version of Firefox which can take advantage indexes here:
> http://pearce.org.nz/video/firefox-indexed-ogg-seek.linux.tar.bz2
> http://pearce.org.nz/video/firefox-indexed-ogg-seek.macosx.dmg
> http://pearce.org.nz/video/firefox-indexed-ogg-seek.win32.zip
>
> Then point that browser here:
> http://pearce.org.nz/video/indexed-seek-demo.html
> (There's a couple of other indexed ogg files in
> http://pearce.org.nz/video/ too)
>
> In terms of compatibility, currently the following players can play and
> seek in indexed files (i.e. aren't broken when playing/seeking indexed
> files):
> * VLC
> * Cortardo
> * XiphQT plugin
>
> The following players can play indexed files, but can't seek:
> * Anything that uses liboggz (including Firefox 3.5).
> * The DirectShow filters (do these use liboggz?)
>
> It only takes a pretty trivial patch to enable liboggz (and thus FF3.5)
> to seek in files with an index; liboggz refuses to seek because it
> doesn't understand metrics for the index track. It shouldn't be too hard
> to fix other players as well.
>
> Totem on Ubuntu9.04 refuses to play the indexed files, though it decodes
> the first few frames. That may require a gstreamer patch.
>
> So... what do you guys think?
>
>
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