[gst-devel] Saving a live stream

[Arnout Vandecappelle]

On Saturday 24 January 2009 09:58:42 Hayden Andrews wrote:
> First of all, I wrote a quick Perl script which reads directly from the
> appropriate HTTP port (an Icecast Server) and writes to a file.
> Everything looks fine with this file except ..
>   1) Suppose we record from 40 mins to 1:20 of the live stream. When we
> play the file, the current time starts at the time we started recording
> from rather than from 00:00. Although the run time is correct (40 mins),
> the current time progresses from 40mins to 1:20.

 That's because the buffer timestamps are retained.  You have to re-stamp the 
buffers.  I ended up writing an element to do exactly that: 
http://bugzilla.gnome.org/show_bug.cgi?id=561224 - that bugzilla entry also 
contains a remark on how it should be done by setting base_time, but I don't 
think that will work.  As discussed earlier on the list (see 
http://thread.gmane.org/gmane.comp.video.gstreamer.devel/22806 ), you can 
also try an identity with single-segment=true, although I also doubt that 
will work :-).

 In any case, you'll need to do demuxing and remuxing to get the timestamps in 
your output file.  So your pipeline will look like this:

filesrc location=... ! oggdemux ! identity single-segment=true \
  ! oggmux ! filesink location=...


 Of course, you'll encounter additional problems with audio: you'll need to 
split the pipeline and add queue's, and I'm pretty sure something will go 
wrong with the synchronisation between the timestamps of the audio and video 
channel.

>   2) When someone tries to edit the file to trim each end and make any
> other minor changes that are required, seeking takes forever and the
> editor takes for ever to do things that would normally be quite quick
> with a normal file. I believe that if the file has a play time of about
> 40 mins, then the player says that it will take about 40 mins to do many
> tasks.
>
> I figure that since a live stream has an unknown length, and since it is
> not possible to seek when viewing a live stream, that there is missing
> info in the live stream that needs to be inserted while saving. So, I
> also figure that it would be easy to insert the relevant requirements
> while saving a live stream to file.....

 Indeed, the output file doesn't contain an index, which means the editor 
needs to scan the entire file in order to seek correctly.  The index is only 
written when the muxer receives an EOS event.  Unfortunately, as far as I 
know, there is no way to force an EOS on a stream started with gst-launch.  
How do you select the part you want using GStreamer anyway?

 It may pay off to take a look at gentrans: http://gentrans.sourceforge.net/

 Regards,
 Arnout

-- 
Arnout Vandecappelle                               arnout at mind be
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