Seeking

[Wes Miller]

After looking at about a hundred web pages and the gstreamer online docs, I can’t find the information that I’m apparently just supposed to know.

 

So, can someone please explain how seeking works.  In particular, I want to pick out one JPEG frame from the stream of JPEGS demuxed and saved from an MJPEG stream.  And then, perhaps, to step one pic at a time through the stream.

 

I started by saving an mjpeg live stream into a mkv file thus:

 

gst-launch souphttpsrc location=... do-timestamp=true is_live=true

      !  multipartdemux

      ! matroskamux

      ! filesink location= saved-mjpeg-stream.

 

 Now I am playing it back using this equally simple pipeline:

 

 gst-launch filesrc location=saved-mjpeg-stream.mkv \

      ! matroskademux

      ! jpegdec

      ! ffmpegcolorspace

      ! autovideosink

 

This pipeline is actually coded in C.  So, after I set the pipeline to PAUSED, I’d like to be able to seek to one particular frame that is at a specified  offset in time relative to the start of the saved mjpeg stream.   

 

// …..

 

  gst_element_set_state( pipeline, GST_STATE_PAUSED );

 

// perform a seek here

// then “play” the one frame or

// play N more frames.

 

 

 

FWIW, I have read a mountain of web posts and samples.  All of them tell me what functions to use but no one seems to explain why and how to create an event, where (and where not) to hook it in.   Is there a good online how-to for gstreamer.  No, the online documentation at gstreamer.net just glosses over events and seeking.

 

Wes Miller  

 

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[Tim-Philipp Müller-2]

On Mon, 2010-04-05 at 10:22 -0400, Wesley J. Miller wrote:

Hi,

> This pipeline is actually coded in C.  So, after I set the pipeline to
> PAUSED, I’d like to be able to seek to one particular frame that is at
> a specified  offset in time relative to the start of the saved mjpeg
> stream.  
>
> (...)
>   gst_element_set_state( pipeline, GST_STATE_PAUSED );
>
> // perform a seek here

Are you waiting for the pipeline to preroll / finish the sate change
after doing _set_state(PAUSED)?

Upward state changes to PAUSED/PLAYING are usually asynchronous (you
might want to check the return value of _set_state() if you're not doing
that yet), meaning that when _set_state() returns the pipeline is not in
PAUSED/PLAYING state yet, meaning that you can't seek on it yet.

You can wait for the pipeline to preroll with something like:

  GstMessage *msg;

  msg = gst_bus_timed_pop_filtered (GST_ELEMENT_BUS (pipeline),
      GST_CLOCK_TIME_NONE,
      GST_MESSAGE_ERROR | GST_MESSAGE_ASYNC_DONE);

  if (msg == GST_MESSAGE_ERROR) {
    .. handle error ..
  }
  gst_message_unref (msg);

  gst_element_seek_simple (pipeline, GST_FORMAT_TIME,
      GST_SEEK_FLAG_FLUSH | GST_SEEK_FLAG_ACCURATE,
      5 * GST_SECOND);

  (N.B.: after this the pipeline will need to preroll again)

Some info on frame stepping can be found here (it's not entirely clear
what documentation you have found or not, or what information you're
looking for exactly):

http://cgit.freedesktop.org/gstreamer/gstreamer/tree/docs/design/part-framestep.txt
http://cgit.freedesktop.org/gstreamer/gstreamer/tree/tests/examples/stepping

Hope this helps.

Cheers
 -Tim




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[Wes Miller]

Well, this is going to be harder than I thought it was.

Because the kind help below didn't want to work, I tried just showing the video, no seek.

I learned I can't get autovideosink to actually show video.

So after whittling down the code to a minimum, here is my skeleton of just showing the video:



int main( int argc, char **argv)
  {
  GstElement *pipeline;
  GMainLoop *loop;
   
  gst_init( &argc, &argv );
  loop = g_main_loop_new( NULL, FALSE );

  pipeline = gst_pipeline_new ("pipeline" );
 
// ... dot dot dot ...

  // souphttpsrc ! multipartdemux ! jpegdec ! ffmpegcolorspace ! autovideosink

  gst_bin_add_many( GST_BIN( pipeline ), src, multi_demux, jpegdec, colormapper, videoplayer, NULL);
  gst_element_link_many( src, multi_demux, jpegdec, colormapper, videoplayer, NULL );
 
  g_print("step 1 - start playing. \n" );
   
  gst_element_set_state( pipeline, GST_STATE_PLAYING );
   
  g_print("step 2 - state changed to playing. \n" );

  g_main_loop_run( loop );
   
  g_print("step 3 - after loop is running. \n" );

  /* shutdown everything */
  gst_element_set_state( pipeline, GST_STATE_NULL );

  gst_object_unref (GST_OBJECT (pipeline));
   
  return 0;
  }

Step 2 prints: "step 2 - state changed to playing."
And then it hangs.  No video ever displays.

I also tried this with a filesrc.  Same result.


I DID get output with PLAYBIN and PLAYBIN2.  


So, can someone pick out my error and get me back to where I can TRY the seek stuff?

Thanks,

Wes




-----Original Message-----
From: Tim-Philipp Müller [mailto:[hidden email]]
Sent: Monday, April 05, 2010 2:02 PM
To: [hidden email]
Subject: Re: [gst-devel] Seeking

On Mon, 2010-04-05 at 10:22 -0400, Wesley J. Miller wrote:

Hi,

> This pipeline is actually coded in C.  So, after I set the pipeline to
> PAUSED, I’d like to be able to seek to one particular frame that is at
> a specified  offset in time relative to the start of the saved mjpeg
> stream.  
>
> (...)
>   gst_element_set_state( pipeline, GST_STATE_PAUSED );
>
> // perform a seek here

Are you waiting for the pipeline to preroll / finish the sate change
after doing _set_state(PAUSED)?

Upward state changes to PAUSED/PLAYING are usually asynchronous (you
might want to check the return value of _set_state() if you're not doing
that yet), meaning that when _set_state() returns the pipeline is not in
PAUSED/PLAYING state yet, meaning that you can't seek on it yet.

You can wait for the pipeline to preroll with something like:

  GstMessage *msg;

  msg = gst_bus_timed_pop_filtered (GST_ELEMENT_BUS (pipeline),
      GST_CLOCK_TIME_NONE,
      GST_MESSAGE_ERROR | GST_MESSAGE_ASYNC_DONE);

  if (msg == GST_MESSAGE_ERROR) {
    .. handle error ..
  }
  gst_message_unref (msg);

  gst_element_seek_simple (pipeline, GST_FORMAT_TIME,
      GST_SEEK_FLAG_FLUSH | GST_SEEK_FLAG_ACCURATE,
      5 * GST_SECOND);

  (N.B.: after this the pipeline will need to preroll again)

Some info on frame stepping can be found here (it's not entirely clear
what documentation you have found or not, or what information you're
looking for exactly):

http://cgit.freedesktop.org/gstreamer/gstreamer/tree/docs/design/part-framestep.txt
http://cgit.freedesktop.org/gstreamer/gstreamer/tree/tests/examples/stepping

Hope this helps.

Cheers
 -Tim




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[Ron McOuat]

Comments inline below

On 10-04-05 1:34 PM, Wesley J. Miller wrote:

> Well, this is going to be harder than I thought it was.
>
> Because the kind help below didn't want to work, I tried just showing the video, no seek.
>
> I learned I can't get autovideosink to actually show video.
>
> So after whittling down the code to a minimum, here is my skeleton of just showing the video:
>
>
>
> int main( int argc, char **argv)
>    {
>    GstElement *pipeline;
>    GMainLoop *loop;
>
>    gst_init(&argc,&argv );
>    loop = g_main_loop_new( NULL, FALSE );
>
>    pipeline = gst_pipeline_new ("pipeline" );
>
> // ... dot dot dot ...
>
>    // souphttpsrc ! multipartdemux ! jpegdec ! ffmpegcolorspace ! autovideosink
>    

What happens when you put the pipeline above into the gst-launch command
with -v and -m as options
to provide extra status messaging? Your pipeline looks right for display
of MJPEG provided the device at
souphttpsrc location="URL of decice in MJPEG mode" is cooperating.
>    gst_bin_add_many( GST_BIN( pipeline ), src, multi_demux, jpegdec, colormapper, videoplayer, NULL);
>    gst_element_link_many( src, multi_demux, jpegdec, colormapper, videoplayer, NULL );
>
>    g_print("step 1 - start playing. \n" );
>
>    gst_element_set_state( pipeline, GST_STATE_PLAYING );
>    
The state change is asynchronous and the return status is not checked to
be sure the call was accepted.
>
>    g_print("step 2 - state changed to playing. \n" );
>
>    g_main_loop_run( loop );
>    
This does not return until g_main_loop_quit is called from another
thread such as in the Error / EOS handler you should have
set up for the pipeline as a message callback.
There should also be a callback to set up the association between the
video sink and the window you need to provide as part
of the program GUI for the video to be rendered in.

I can see that you are using C but this documentation for Python will
give you a good idea of how a program
needs to be set up to link a pipeline to a video playback window and to
handle the end of stream. It adds another layer
with the GTK GUI library but looking at the overall structure should
help you. I don't know what system you are on
so unless you use a somewhat system agnostic GUI library how you
actually get the window ID will differ
significantly between system types.

Here is the Python tutorial URL:

http://pygstdocs.berlios.de/pygst-tutorial/index.html

with several example programs.

>
>    g_print("step 3 - after loop is running. \n" );
>
>    /* shutdown everything */
>    gst_element_set_state( pipeline, GST_STATE_NULL );
>
>    gst_object_unref (GST_OBJECT (pipeline));
>
>    return 0;
>    }
>
> Step 2 prints: "step 2 - state changed to playing."
> And then it hangs.  No video ever displays.
>
> I also tried this with a filesrc.  Same result.
>
>
> I DID get output with PLAYBIN and PLAYBIN2.
>
>
> So, can someone pick out my error and get me back to where I can TRY the seek stuff?
>
> Thanks,
>
> Wes
>
>
>
>
> -----Original Message-----
> From: Tim-Philipp Müller [mailto:[hidden email]]
> Sent: Monday, April 05, 2010 2:02 PM
> To: [hidden email]
> Subject: Re: [gst-devel] Seeking
>
> On Mon, 2010-04-05 at 10:22 -0400, Wesley J. Miller wrote:
>
> Hi,
>
>    
>> This pipeline is actually coded in C.  So, after I set the pipeline to
>> PAUSED, I’d like to be able to seek to one particular frame that is at
>> a specified  offset in time relative to the start of the saved mjpeg
>> stream.
>>
>> (...)
>>    gst_element_set_state( pipeline, GST_STATE_PAUSED );
>>
>> // perform a seek here
>>      
> Are you waiting for the pipeline to preroll / finish the sate change
> after doing _set_state(PAUSED)?
>
> Upward state changes to PAUSED/PLAYING are usually asynchronous (you
> might want to check the return value of _set_state() if you're not doing
> that yet), meaning that when _set_state() returns the pipeline is not in
> PAUSED/PLAYING state yet, meaning that you can't seek on it yet.
>
> You can wait for the pipeline to preroll with something like:
>
>    GstMessage *msg;
>
>    msg = gst_bus_timed_pop_filtered (GST_ELEMENT_BUS (pipeline),
>        GST_CLOCK_TIME_NONE,
>        GST_MESSAGE_ERROR | GST_MESSAGE_ASYNC_DONE);
>
>    if (msg == GST_MESSAGE_ERROR) {
>      .. handle error ..
>    }
>    gst_message_unref (msg);
>
>    gst_element_seek_simple (pipeline, GST_FORMAT_TIME,
>        GST_SEEK_FLAG_FLUSH | GST_SEEK_FLAG_ACCURATE,
>        5 * GST_SECOND);
>
>    (N.B.: after this the pipeline will need to preroll again)
>
> Some info on frame stepping can be found here (it's not entirely clear
> what documentation you have found or not, or what information you're
> looking for exactly):
>
> http://cgit.freedesktop.org/gstreamer/gstreamer/tree/docs/design/part-framestep.txt
> http://cgit.freedesktop.org/gstreamer/gstreamer/tree/tests/examples/stepping
>
> Hope this helps.
>
> Cheers
>   -Tim
>
>
>
>
> ------------------------------------------------------------------------------
> Download Intel® Parallel Studio Eval
> Try the new software tools for yourself. Speed compiling, find bugs
> proactively, and fine-tune applications for parallel performance.
> See why Intel Parallel Studio got high marks during beta.
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> _______________________________________________
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> [hidden email]
> https://lists.sourceforge.net/lists/listinfo/gstreamer-devel
> ------------------------------------------------------------------------------
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> Try the new software tools for yourself. Speed compiling, find bugs
> proactively, and fine-tune applications for parallel performance.
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> https://lists.sourceforge.net/lists/listinfo/gstreamer-devel
>    

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[Wes Miller]

Many, many thanks, Ron.

Comments inserted below.  

-----Original Message-----
From: Ron McOuat [mailto:[hidden email]]

>>    // souphttpsrc ! multipartdemux ! jpegdec ! ffmpegcolorspace ! autovideosink
>>    

> What happens when you put the pipeline above into the gst-launch command
> with -v and -m as options
> to provide extra status messaging?

==============================================================================
I did some column alignment to me read it.....
Can these same -v and -m flags be set from a compiled program?  Requires callbacks?

Setting pipeline to PAUSED ...
Pipeline is live and does not need PREROLL ...
Got message #8 from element  "autovideosink0"   (state-changed): GstMessageState, old-state=(GstState)GST_STATE_NULL, new-state=(GstState)GST_STATE_READY, pending-state=(GstState)GST_STATE_VOID_PENDING;
Got message #9 from element  "ffmpegcsp0"       (state-changed): GstMessageState, old-state=(GstState)GST_STATE_NULL, new-state=(GstState)GST_STATE_READY, pending-state=(GstState)GST_STATE_VOID_PENDING;
Got message #10 from element "jpegdec0"         (state-changed): GstMessageState, old-state=(GstState)GST_STATE_NULL, new-state=(GstState)GST_STATE_READY, pending-state=(GstState)GST_STATE_VOID_PENDING;
Got message #11 from element "multipartdemux0"  (state-changed): GstMessageState, old-state=(GstState)GST_STATE_NULL, new-state=(GstState)GST_STATE_READY, pending-state=(GstState)GST_STATE_VOID_PENDING;
Got message #12 from element "souphttpsrc0"     (state-changed): GstMessageState, old-state=(GstState)GST_STATE_NULL, new-state=(GstState)GST_STATE_READY, pending-state=(GstState)GST_STATE_VOID_PENDING;
Got message #13 from element "pipeline0"        (state-changed): GstMessageState, old-state=(GstState)GST_STATE_NULL, new-state=(GstState)GST_STATE_READY, pending-state=(GstState)GST_STATE_PAUSED;
Got message #16 from element "ffmpegcsp0"       (state-changed): GstMessageState, old-state=(GstState)GST_STATE_READY, new-state=(GstState)GST_STATE_PAUSED, pending-state=(GstState)GST_STATE_VOID_PENDING;
Got message #17 from element "jpegdec0"         (state-changed): GstMessageState, old-state=(GstState)GST_STATE_READY, new-state=(GstState)GST_STATE_PAUSED, pending-state=(GstState)GST_STATE_VOID_PENDING;
Got message #18 from element "multipartdemux0"  (state-changed): GstMessageState, old-state=(GstState)GST_STATE_READY, new-state=(GstState)GST_STATE_PAUSED, pending-state=(GstState)GST_STATE_VOID_PENDING;
Got message #21 from pad     "souphttpsrc0:src" (stream-status): GstMessageStreamStatus, type=(GstStreamStatusType)GST_STREAM_STATUS_TYPE_CREATE, owner=(GstElement)"\(GstSoupHTTPSrc\)\ souphttpsrc0", object=(GstTask)"\(GstTask\)\ task0";
Got message #22 from element "souphttpsrc0"     (state-changed): GstMessageState, old-state=(GstState)GST_STATE_READY, new-state=(GstState)GST_STATE_PAUSED, pending-state=(GstState)GST_STATE_VOID_PENDING;
Got message #23 from element "pipeline0"        (state-changed): GstMessageState, old-state=(GstState)GST_STATE_READY, new-state=(GstState)GST_STATE_PAUSED, pending-state=(GstState)GST_STATE_VOID_PENDING;
Setting pipeline to PLAYING ...
Got message #24 from element "pipeline0"        (new-clock): GstMessageNewClock, clock=(GstClock)"\(GstSystemClock\)\ GstSystemClock";
New clock: GstSystemClock
Got message #25 from element "ffmpegcsp0"       (state-changed): GstMessageState, old-state=(GstState)GST_STATE_PAUSED, new-state=(GstState)GST_STATE_PLAYING, pending-state=(GstState)GST_STATE_VOID_PENDING;
Got message #26 from element "jpegdec0"         (state-changed): GstMessageState, old-state=(GstState)GST_STATE_PAUSED, new-state=(GstState)GST_STATE_PLAYING, pending-state=(GstState)GST_STATE_VOID_PENDING;
Got message #27 from element "multipartdemux0"  (state-changed): GstMessageState, old-state=(GstState)GST_STATE_PAUSED, new-state=(GstState)GST_STATE_PLAYING, pending-state=(GstState)GST_STATE_VOID_PENDING;
Got message #28 from element "souphttpsrc0"     (state-changed): GstMessageState, old-state=(GstState)GST_STATE_PAUSED, new-state=(GstState)GST_STATE_PLAYING, pending-state=(GstState)GST_STATE_VOID_PENDING;
Got message #29 from pad     "souphttpsrc0:src" (stream-status): GstMessageStreamStatus, type=(GstStreamStatusType)GST_STREAM_STATUS_TYPE_ENTER, owner=(GstElement)"\(GstSoupHTTPSrc\)\ souphttpsrc0", object=(GstTask)"\(GstTask\)\ task0";

/GstPipeline:pipeline0/GstJpegDec:jpegdec0.GstPad:sink: caps = image/jpeg
/GstPipeline:pipeline0/GstJpegDec:jpegdec0.GstPad:src: caps = video/x-raw-yuv, format=(fourcc)I420, width=(int)704, height=(int)480, framerate=(fraction)0/1
/GstPipeline:pipeline0/GstFFMpegCsp:ffmpegcsp0.GstPad:src: caps = video/x-raw-yuv, width=(int)704, height=(int)480, framerate=(fraction)0/1, format=(fourcc)YV12
/GstPipeline:pipeline0/GstFFMpegCsp:ffmpegcsp0.GstPad:sink: caps = video/x-raw-yuv, format=(fourcc)I420, width=(int)704, height=(int)480, framerate=(fraction)0/1
/GstPipeline:pipeline0/GstAutoVideoSink:autovideosink0/GstDshowVideoSink:autovideosink0-actual-sink-dshowvideo.GstPad:sink: caps = video/x-raw-yuv, width=(int)704, height=(int)480, framerate=(fraction)0/1, format=(fourcc)YV12
/GstPipeline:pipeline0/GstAutoVideoSink:autovideosink0.GstGhostPad:sink: caps = video/x-raw-yuv, width=(int)704, height=(int)480, framerate=(fraction)0/1, format=(fourcc)YV12
/GstPipeline:pipeline0/GstAutoVideoSink:autovideosink0.GstGhostPad:sink.GstProxyPad:proxypad0: caps = video/x-raw-yuv, width=(int)704, height=(int)480, framerate=(fraction)0/1, format=(fourcc)YV12

Got message #34 from element "autovideosink0-actual-sink-dshowvideo" (state-changed): GstMessageState, old-state=(GstState)GST_STATE_READY, new-state=(GstState)GST_STATE_PAUSED, pending-state=(GstState)GST_STATE_VOID_PENDING;
Got message #37 from element "autovideosink0"                        (state-changed): GstMessageState, old-state=(GstState)GST_STATE_READY, new-state=(GstState)GST_STATE_PAUSED, pending-state=(GstState)GST_STATE_VOID_PENDING;
Got message #38 from element "pipeline0"                             (async-done): no message details
Got message #40 from element "autovideosink0-actual-sink-dshowvideo" (element): prepare-xwindow-id;
Got message #41 from element "autovideosink0-actual-sink-dshowvideo" (element): have-xwindow-id, xwindow-id=(gulong)264922;
Got message #42 from element "autovideosink0-actual-sink-dshowvideo" (state-changed): GstMessageState, old-state=(GstState)GST_STATE_PAUSED, new-state=(GstState)GST_STATE_PLAYING, pending-state=(GstState)GST_STATE_VOID_PENDING;
Got message #43 from element "autovideosink0"                        (state-changed): GstMessageState, old-state=(GstState)GST_STATE_PAUSED, new-state=(GstState)GST_STATE_PLAYING, pending-state=(GstState)GST_STATE_VOID_PENDING;
Got message #44 from element "pipeline0"                             (state-changed): GstMessageState, old-state=(GstState)GST_STATE_PAUSED, new-state=(GstState)GST_STATE_PLAYING, pending-state=(GstState)GST_STATE_VOID_PENDING;

==============================================================================




> Your pipeline looks right for display of MJPEG provided the device at
> souphttpsrc location="URL of decice in MJPEG mode" is cooperating.

As you can see, the camera is working fine.

> The state change is asynchronous and the return status is not checked to
> be sure the call was accepted.

Next things to learn.

>>    g_main_loop_run( loop );
>>

   
> This does not return until g_main_loop_quit is called from another
> thread such as in the Error / EOS handler you should have
> set up for the pipeline as a message callback.
> There should also be a callback to set up the association between the
> video sink and the window you need to provide as part
> of the program GUI for the video to be rendered in.

More to learn about.

> I can see that you are using C but this documentation for Python will
> give you a good idea of how a program
> needs to be set up to link a pipeline to a video playback window and to
> handle the end of stream. It adds another layer
> with the GTK GUI library but looking at the overall structure should
> help you. I don't know what system you are on
> so unless you use a somewhat system agnostic GUI library how you
> actually get the window ID will differ
> significantly between system types.

> Here is the Python tutorial URL:
> http://pygstdocs.berlios.de/pygst-tutorial/index.html
> with several example programs.

Thanks!



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