Can we check when an element's sink pad receives a buffer to add custom data to it

[Nostalgia]

Hi,

Hope someone can help me in the following :

1) How we can detect the arriving of buffers to an element's sink pad ?
If (1) is possible :
2) Can we add a callback to a function that indicating that sink pad has
received a buffer to do some modifications to this buffer or to add extra
custom data to it ?

If (1) isn't possible : when adding meta data to a buffer, is this extra
data will be processed by other elements or it will be transmitting from one
element to another without modifying ? (e.g. if i add a metadata to a buffer
pushed through my appsource, when an encoder element receives this buffers,
it will compress the metadata with the initial buffer ?)

Hope that I succeed to transmit what I need clearly !

Regards,



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