Part of the code expects valid lists, in particular no duplicates.
These tests allow to catch bugs in filters (unlikely but possible)
and to give a clear message when the error comes from the user
((a)formats) or the application (buffersink).
If we decide to switch to a more efficient merging algorithm,
possibly sorting the lists, these functions will be the preferred
place for pre-processing, and can be renamed accordingly.
projects / ffmpeg / commit