role of timestamp in GstBuffer

[Massimiliano Cialdi]

hallo,

trying to make a test I noticed a strange behavior of timestamp in 
GstBuffer.

here is a simplified chain function:

/* chain function
  * this function does the actual processing
  */
static GstFlowReturn
gst_myconverter_chain (GstPad * pad, GstBuffer * buf)
{
     Gstmyconverter *filter;
     GstFlowReturn ret;

     filter = GST_MYCONVERTER (GST_OBJECT_PARENT (pad));

     GstBuffer     *outBuf;
     outBuf = (GstBuffer*)gst_buffer_copy(buf);

     guint          numSamples;

     numSamples = 
(GST_BUFFER_SIZE(buf)/(filter->stream.width/8))/filter->stream.channels;

     GST_BUFFER_DURATION (outBuf) = GST_FRAMES_TO_CLOCK_TIME(numSamples, 
filter->stream.sampleRate);

     filter->totalDuration  += GST_BUFFER_DURATION (outBuf);

     if(filter->useTimeStamp)
         GST_BUFFER_TIMESTAMP(outBuf)    = filter->totalDuration;
     else
         GST_BUFFER_TIMESTAMP(outBuf)    = GST_CLOCK_TIME_NONE;

     ret = gst_pad_push (filter->srcpad, outBuf);
     gst_buffer_unref(buf);

     return ret;
}


that is, if timestamp is GST_CLOCK_TIME_NONE it works well.
If timestamp is actual elapsed time it doesnt works. It seems to be much 
faster.

why this behaviour?
what is the correct value to be assigned to timestamp?

best regards

Max
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