[gst-devel] When to do initial seek; segment seek problems

[Артём Попов]

Hi guys!
I've been trying to put together a small gstreamer app and ran into 2 problems:
(using gst-python, all libs and plugins from latest 0.10 tarballs)

1. I want to play a small chunk of a media file using playbin.
However, when I call the seek routine immediately after starting the
pipeline, element_seek returns TRUE but no seeking is done:

        playbin.set_state (gst.STATE_PLAYING)
        playbin.seek (1.0, gst.FORMAT_TIME, gst.SEEK_FLAG_ACCURATE |
gst.SEEK_FLAG_FLUSH | gst.SEEK_FLAG_SEGMENT, gst.SEEK_TYPE_SET,	25 *
gst.SECOND, gst.SEEK_TYPE_SET, 35 * gst.SECOND)

I'm calling seek too early here... So I guess that I should call seek
right immediately after some event has happened: a handoff,
notify_caps or something like that, right? I.e. when the pipeline
knows more of its media stream? How could I do that??

2. I wrote a little python script to test loop-with-segment-seek
behaviour (attached). It shows rather weird behaviour with any codec,
that I tried to test, except WAV. I shall describe the behaviour
below, because I'm almost sure there're bugs in the appropriate
plugins:

* WAV:
Works okay, loops seamlessly, even with SEEK_FLAG_ACCURATE.

* Ogg Vorbis:
Starts to loop, but shortly after that (~1/2 of supposed loop) sound
goes off and I see huge CPU load in the System Monitor Applet.
When time comes for the loop to start over, it starts over ok with
sound, then again sound goes off and I see huge CPU load again...

* MP3 (cbr & vbr):
The segment starts much earlier than supposed to. Lasts also much
shorter than supposed to.
Then the playbin spawns lots of SEGMENT_DONE messages one immediately
after another, playback position advances far beyond stream duration
to infinity, no sound at all.

* FLAC:
Sends EOS message instead of SEGMENT_DONE, although there's
FLAG_SEGMENT set during seek. This is surely a bug. Requires
SEEK_FLAG_FLUSH when restarting loop after that, which I think
controverses with this:
http://webcvs.freedesktop.org/gstreamer/gstreamer/docs/design/part-seeking.txt?view=markup

* Fluendo mp3 plugin from SVN:
I think this one does not know anything about segments. Emits neither
EOS nor SEGMENT_DONE upon completion and continues to play happily
beyond segment-end-point :(

As, I already said, WAV works perfectly, so there're probably bugs in
the other plugins. Could anyone with a bugzilla access file the bugs
against these problems?

Then again, maybe I'm doing something wrong, so I've attached the test
program for interested people to try out. Change URI and START/STOP
constants in the beginning of the file to test different codecs. The
script plays file for 5 seconds, then seeks to the specified position,
continuously printing current playback position.

Thanks in advance for any hints on my problem!
--Artem
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