Hey Romain, Thanks for clarifying that up, so maybe we will have the ability
to jump to different positions in tracks for Liquidsoap 2.0 :).
I'm going to do some tests this week to see which is faster: Cutting off the
first 50 minutes of an mp3/ogg file, or having liquidsoap "process" all data
up to the 50 minute mark. I'll post my results here.
Thanks!
Martin
2011/4/29 Romain Beauxis <[email protected]>
> Hi!
>
> 2011/4/29 Martin Konečný <[email protected]>:
> > Hi Samuel,
> > Regarding Ticket # LS-469: http://dev.sourcefabric.org/browse/LS-469
> > Could you detail why Liquidsoap would have a very high CPU usage if I
> were
> > to set a cue point more than a few seconds from the beginning of a track?
> > One use-case we were hoping to address with this feature was restarting
> > playback from a specific point in a track after a power failure. One of
> our
> > users has a radio station in an area where the power goes out a few times
> a
> > day, and some of their tracks are pre-recorded shows up to an hour long.
> > We wanted to make it so that if the power goes out with 10 min left of a
> one
> > hour show, they simply need to restart their system and we use liquidsoap
> to
> > jump to the 50 min mark.
>
> That's a very interesting case!
>
> > I am curious why I can jump to any point in a track with media players
> such
> > as Banshee and Rhythmbox instantaneously, but Liquidsoap cannot.
>
> The problem is that Liquidsoap has always been designed as a _stream_
> processing "engine". It works chunk by chunk to generate a stream.
> This internal specification is very appropriate for many reasons but
> also entails some limitations (one of which being the skip vs.
> crossfade problem you mentioned and on which I still have to reply..)
>
> When decoding a file, liquidsoap processes data frame by frame until
> it ends. It has some limited view concerning the future, namely an
> estimation of the remaining time for files and, in the case of
> crossfade in conservative mode, a small buffer of data (which should
> be the solution for your skip and cross issue: pass conservative=true
> to the crossfade operator).
>
> So, for now, we do not have any notion of skiping data in file
> decoders. The cue point operator is implemented for now by decoding
> all the data to skip at once at the beginning of the track and that is
> what may cause high CPU usage. (the problem does not occur at the end
> of the track).
>
> Ideally, we should have a notion of skipping for file decoders.
> However, I am not so sure about how this could be implemented. I
> believe that it could be a source's property, that is only available
> when possible (i.e. the source is a playlist, single but not
> input.http etc..)
> However, this probably requires a fairly large amount of work and
> would also require the implementation of a skipping method for each
> format (and don't get me started on the mess concerning mp3 data..)
> (or the ogg muxing format also..) :-)
>
> All in all, I would say the following:
> * For now Sam's operator is nice for cue points that are close to the
> beginning of the file, which is usually the case for instance with
> crossfading.
> * For you specific case, a cut_file protocol would probably be enough
> (files are mp3 or ogg/vorbis?).
>
> In the long term, I would like to have a skiping data support in
> liquidsoap. However, I believe that is too much of a core change for
> now, because we are still working on the 1.0 stable release...
>
>
> Romain
>
> > Regards,
> > Martin
> > P.S. Thanks for the quick implementation of this feature. Even in its
> > current state we will have uses for it :)
> >
> > --
> > Martin Konecny
> > Software Developer, Sourcefabric
> > [email protected]
> >
> >
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>
--
Martin Konecny
Software Developer, Sourcefabric
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