MLV IDX files should be read and generated

[Andrew Baldwin]

To avoid reindexing MLV files, a seperate IDX file should be generated once indexing is completed during playback. It should be loaded next time the same file is played.

IDX files are produced by the in-camera MLV viewer, and mlv_dump tools, so may already exist.

[Andrew Baldwin]

Unfortunately IDX files are not so useful as they only record the location of chunks, and they do not collect any key data such as the frame number.

Since we will have other clip specific data we will need to record in future (white balance, LUT, corrupt frames, in/out points) perhaps that future file will also include a more complete index (unfortunately not compatible with other MLV tools).