Hm? That does not explain it in detail anyway what you are planning to do, but perhaps it might be better for you to read from the SDRAM directly like with the FrameReader Altera provides. That one can generate you the Frame around the pixeldata the CVO needs to output an image and then you might build a module in VHDL that implements your write access.
From the SDRAm you cannot normally get the data out to the CVO directly I think. It could be that the FrameBuffer also throws away the datapacket around the incoming data and generates a new one when it reads. I try something quite similar, to write a frame directly into sdram and read it from there again to output to the DVI-Monitor and my result is to implement an module, that takes the CVI-data via Avalon-ST, throws away the sof, eof. Writes the pixeldata at a specified address into sdram and on the other side the Framereader from Altera reads the SDRAM continuously where the whole frame is stored and outputs it to the CVO with the sourrounding data. That works quite well when you are using the SDRAM-Controller, because otherwise you will have to manage the accesses from the writer and reader to the sdram with some extra logic. I implemented for the writing to sdram an Avalon-MM interface into my written module, Input is Avalon-ST and you can also implement easily an CSR-Interface to manipulate something while at runtime.
It is just my two cent, but perhaps that gives you another idea. I don't know if this matches what you do in any kind, but I just wanted to tell it anyway ;-)
Have a nice weekend and good luck with your university project, Peet.