[Matroska-devel] About mkclean and attachment placement

Steve Lhomme slhomme at matroska.org
Thu May 27 09:21:07 CEST 2010

Hi Ben,

Are you sure that all the demuxers look for attachments prior playback ?
That doesn't sound efficient if there is no subtitles in the file anyway.

Also seeking is only bad when streamed over a slow connection. On a local
file or local network, you will not see a noticeable difference where the
attachments are located. It may only have an impact when playing files from
the web. And even though, it would be odd to read 3 MB of font before
playback if the user is never going to chose subtitles.


On Thu, May 27, 2010 at 1:51 AM, Ben Danper <sebten at live.com> wrote:

> Hi,
> I've been testing mkclean, it works pretty well.
> However I noticed it places attachments at the end, unlike some other
> muxers. Then I found http://www.matroska.org/technical/order/index.htmlwhich suggests that attachment placement. It makes sense in general terms,
> however it's based on the assumption that "Attachments are not meant to use
> by default when playing the file."
> A large (the largest?) use case of attachments seems to be embedded fonts
> for subtitles, which need to be read before playback starts.
> To make matters worse, demuxers that support fonts (pretty much all
> demuxers used on desktop apps, at least Haali's, libavformat's, mplayer's
> and VLC's) have no way to know whether the attachments contain fonts or not
> beforehand. The end result is that they'll seek to the end of file if there
> are any attachments.
> So I think at least font attachments should be placed at the front. It
> isn't very important in the grand scheme of things but it would be a nice
> touch.
> Thanks
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