Developing DSP software, am I 10 years too late?
DSP is a wide field and goes beyond audio/video processing. And, since new digital devices are developed in any field, DSP algorithm implementation, simulation and design is still a very important area. 

Some examples that come to my mind beyond audio/video:


wireless communications: for example there is plenty of research going on in 5G cellular (i.e. mobile phones) and 802.11 (i.e. WiFi) standards.
medical devices: more and more devices operate (semi-)automatically, requiring sophisticated signal processing to interpret their measurements.
DSL: as users search for faster internet, the research on DSL improvement is very important.
Big Data and deep learning: On the one hand, it's about designing low-complexity algorithms to solve the problems of huge sizes. On the other hand, it's about providnig hardware that can do these operations quickly.


This list is not at all exhaustive, and there are many more fields, where DSP is absolutely necessary and new techniques are developed on a daily basis.