STM32F407VG DCMI - Ethernet - External Memory

Hello. I am a student participating in a project.

I have to take 1080x720px at least 15 fps video feed and forward it (along some other sensor data) through ethernet connection. My question is;

How can I store that data on a external memory unit and later send it with ethernet interface  ?

( When the image size is small the data can directly be stored on sram with dma but my image(s) are 1-1.5 mb in size so this is the reason why i think i need an external memory unit . But if there is a way to send the image data (without capturing the whole frame first) from ethernet interface that would be okay but i researched for 2 weeks and i do not think it is possible.)

I will later design a pcb

Thank you in advance