Implementing a media player using Gstreamer: Mapping the STOPPED state

[Federico Zamperini]

Hi,
	when I want to stop a pipeline I set it to the NULL state (see 
http://gstreamer.freedesktop.org/data/doc/gstreamer/head/manual/html/section-elements-states.html). 
When you go to the NULL state the pipeline is flushed and all the 
resources are freed, so next time you start the pipeline (moving it to 
the PLAYING state) you don't need to seek back to the beginning of the 
stream.
Cheers

Federico

Il 04/12/2012 12:30, Mandeep Sandhu ha scritto:
> Hi All,
>
> I'm implementing a media player on an embedded board. I'm using
> Gstreamer for the actual media playback (the chip vendor provides us
> with some proprietary plugins for H264/AAC decoding and audio/video
> sinks for the specific hardware).
>
> Currently I'm concentrating on just playing MP4/H264/AAC files (other
> formats will be supported later when I figure out how to do
> auto-detection! :))
>
> My gst pipeline essentially looks like this:
>
> file-source -> qtdemux -> h264dec -> vsink
>                          |
>                          +-----> aacdec -> asink
>
>
> So, I have most of the bits worked out, except what state to set on
> the pipeline when I'm in the STOPPED state of my player (eg: a user
> pressed the STOP button on the player or the stream ended (EOS)).
>
> Initially I thought setting the pipeline to READY state would do it
> but that turned out to be wrong. Reading docs on GST_MESSAGE_EOS
> revealed that the EOS event is retained in the elements and has to be
> flushed explicitly.
>
> I have the state of my player being tracked by state machine, so the
> SM transitions to the STOPPED state on either an explicit command (by
> the user) or when the EOS message appears on the pipeline's bus.
>
> So I wrote some code to flush the pipeline and then set it to the
> PAUSED state (since I don't want playback to start automatically).
> Here's what I do when going into the STOPPED state:
>
> gst_element_seek(m_pipeline, 1.0, GST_FORMAT_TIME,
>                       GST_SEEK_FLAG_FLUSH, GST_SEEK_TYPE_SET,
>                       0, GST_SEEK_TYPE_NONE,  0);
> gst_element_set_state (m_pipeline, GST_STATE_PAUSED);
>
> Is this correct way to handle the scenario described or is there a
> better/recommended way of going about it?
>
> I basically want the stream playback position to be set to the start
> so that a play command will cause it to play the file from the
> beginning.
>
> Any pointers appreciated.
>
> Thanks,
> -mandeep
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