Question

I have created a mjpeg stream. I have embedded content length in between the two jpeg frames [between footer of first frame and header of the next frame].

[MJPEG STREAM]
      |
      V
...
----------
JPEG FRAME
(Image)
----------
Content-length
(Text)
----------
JPEG FRAME
(Image)
----------
Content-length
(Text)
----------
JPEG FRAME
(Image)
----------
...
      |
      V

I am able to play the video using gstreamer-java, gstreamer C API and gst-launch. However I am trying to parse the content-length text in gstreamer-java. I tried “meta tags” but that doesn’t yield any result I need

I play mjpeg stream that I created as follows

gst-launch -v souphttpsrc location="<ip>:<port>/<cgi_bin folder>/<name>.cgi" do-timestamp=true is_live=true ! multipartdemux ! jpegdec ! ffmpegcolorspace ! autovideosink

I tried meta tags using

gst-launch -v souphttpsrc location="<ip>:<port>/<cgi_bin folder>/<name>.cgi" do-timestamp=true is_live=true ! multipartdemux ! jpegdec ! fakesink -t

and this

gst-launch -v souphttpsrc location="<ip>:<port>/<cgi_bin folder>/<name>.cgi" do-timestamp=true is_live=true ! fakesink -t

However the output of this media pipeline is something like the following

/GstPipeline:pipeline0/GstFakeSink:fakesink0: last-message = "chain   ******* < (557568   
bytes, timestamp: 0:00:06.895505695, duration: none, offset: -1, offset_end: -1, flags: 
0) 0x9a82818"
/GstPipeline:pipeline0/GstFakeSink:fakesink0: last-message = "chain   ******* < (557568 
bytes, timestamp: 0:00:06.941328354, duration: none, offset: -1, offset_end: -1, flags: 
0) 0x9a6f6e0"

As it can be seen no content-length. 🙁 . I use WireShark and see data packets containing content-length. Subsequently I wrote a separate Java Code (with no gstreamer plugins) and I can parse the stream to get the content length. However this is not the ideal method as I want the content-length corresponding to the exact frame keeping in view the synchronization.

I have written tees before for C API code. I am wondering if tee would work in this instance!

Answer 1

Appsink came in handy. The pipeline looks like

                         _ queue -> appsink -> parser 
                       /  
        video -> tee ->
                       \_ demux -> decoder -> ffmpegcolorspace -> autovideosink 

The Java Code snippet looks like

First define the appsink bin

final AppSink appsink = (AppSink) ElementFactory.make("appsink", "appsink");

Then its properties …

appsink.set("emit-signals",true);
appsink.set("max-buffers",1);
//appsink.set("drop",true); //Make this non-blocking. 
                            //Meaning drop frames when queue is full

Then its function …

appsink.connect(new AppSink.NEW_BUFFER() {
@Override public void newBuffer(Element elem, Pointer userData) {
AppSink appsink = (AppSink) elem;
Buffer buffer = appsink.pullBuffer();  //get the stream data as an input to external 
                                       //applications

/*
// Create a character ByteBuffer
CharBuffer cbuf = byteBuffer.asCharBuffer();
*/

ByteBuffer byteBuffer = buffer.getByteBuffer();
byte[] bytearray = new byte[byteBuffer.remaining()];
byteBuffer.get(bytearray);
String s = new String(bytearray);
//InputStream is = new ByteArrayInputStream(bytearray);
// System.out.print(buffer.getSize()+"\n");
//  System.out.print(s+"\n");

//Do whatever with this buffer inside string here e.g. parsing text content

...

byteBuffer.clear();
buffer.dispose();
buffer = null;

}
});           

//===========================================================================

The C code snippet looks like

...
sink = gst_element_factory_make ("appsink", "Output");
g_assert (sink);

Then…

...
gst_app_sink_set_max_buffers((GstAppSink*)sink, 100);
gst_app_sink_set_emit_signals ((GstAppSink*)sink, TRUE);
g_signal_connect (sink, "new-buffer",  G_CALLBACK(new_buffer), NULL);

Then…

static GstFlowReturn new_buffer (GstAppSink *app_sink, gpointer user_data)
{
  char* pipe_name = (char*) user_data;
  GstBuffer* buffer = gst_app_sink_pull_buffer(app_sink);

//  g_debug("appsink buffer timestamp(%lli) size(%d)",
//          GST_BUFFER_TIMESTAMP(buffer),
//          GST_BUFFER_SIZE(buffer));

  g_print((char*)buffer);

  gst_buffer_unref(buffer);
  return GST_FLOW_OK;
}