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+We need a mechanism to transport extra data in a GstBuffer. Unlike caps the content is likely to change for each buffer. 
+
+Examples: 
+
+* Pan and scan (video subregion) position information 
+* interlacing markers (top field, bottom field) 
+* theora granulepos, instead of slapping it in the 'offset' field 
+* MPEG Decoding timestamps, which we currently never send along. 
+* Feature-Extraction elements can add feature data 
+* Some image capture sensors can provide histograms with the frames 
+      * Some formats (mpeg-ts from HDV cameras) provide date/gain/shutter-speed/scene-change at a regular interval but not for every frame (around 10 times per second). 
+* packet priority and timeout could be used by network plugins (such as DCCP) to send more important packets when congestion is detected. 
+Ideas: 
+
+1. GstStructure in GstBuffer 
+1. GstTaglist in GstBuffer 
+1. syncronized downstream events 
+1. Store GstStructures in GstIndex 
+GstStructure is also use in GstTaglist. The structure can be hierarchical. We could require that the producer uses its element name as a root tag. This way the taglist could carry multiple data-sets identified in a unique way. Elements that can use the data need to know the name of the element that created it. 
+
+Issues: 
+
+* Performance 
+   * copying, freeing buffers need to check/handle the presence of extra metadata 
+* Transformations 
+   * there might be transformation that render the data useless. e.g. if the data is a histogram, color changes invalidate it. if its a sub-region, size changes invalidate it. 
+* Mixing 
+   * if we go for (B) we could use the tag merge modes 
+* Muxing 
+   * using and/or dropping the data, it does not sound sensible to send it further 
+* Copies (tee) 
+   * make duplicates 
+\ No newline at end of file