Naive question... would it be possible to make a language that describes multimedia formats that could then be automatically converted into code.
1. The translation system would still have to implement the underlying ideas. For example, your spec might explain "key frames are made by doing a wavelet transform ABC, dropping frequency XYZ, applying Heuristic Alpha and then doing LZ encoding on the result" or something like that. You still need implementations of those specific operations. Having to explain all that stuff in the spec would mean each english language doc would be book length tretsie on encoding. As a result, you don't really gain much by doing this kind of meta-explaination.
2. Video encoding/decoding is something where optimization is extremely important. Writing code that is specific to a single purpose is generally going to be faster than generic code that could be applied to any theoretical format. For example, by knowing the exact size of a transformation matrix, you can decide whether to build a lookup table or calculate on the fly - you can use hardware level features that require knowing exact sizes at build-time etc.