Yes, that is a valid point; for some applications, random access will be helpful. One possibility is to make each file as a separate compression block, which i

Yes, that is a valid point; for some applications, random access will be helpful. One possibility is to make each file as a separate compression block, which is possible if using concatenatable compression formats; then, the same format can be used for solid and for non-solid compression. However, then, you will need a index if you want random access. I don't know what compression formats have such a feature as a index, but I thought of some ideas of a (concatenatable) compression format; one possible thing to add is a optional index block (which links the compressed and uncompressed offsets of the beginning of blocks which do not depend on any previous blocks).