I've said it before, I'll say it again. Let the market for the work drive it's copyright term. I think most copyrights should be registered in a database, the only exceptions being works with exteremely short life spans such as news items. Rights holders should get a certain short period of free protection, where the length of the period is dependent on the nature of the work (music recording, video, novel, poem, song lyrics, news broadcast, combinations thereof). The period would be determined factoring the costs of production for the type of work, and the general longevity of the work, e.g. movies aare expensive to make compared to a music album, but less likely to be popular 5 years hence. Production costs proportionally increase the period length for the type of work, and potential longevity proportionally decreases the period, because longevity in popularity extends the commercial viability of the work. At the end of the period, the rights holder may renew the copyright registration for a significant cost, for the same amount of time. At the end of the second period, renewal costs double, and double again for the third renewal etc. In this way the length of a copyright term is tied to the specific work's contribution to society via a market mechanism. As long as the work is profitable, which is an indication that society in general finds it worth while, it is worth while paying the renewal costs. Consider some examples:
1) A successful popular music album. The artist creates the album, registers the copyright, and gets 1 year free copyright protection. In the first year it makes a lot of money, and is still selling well towards the end of the year. The artist renews the copyright for a fee (say 100 euros). At the end of the second year, sales have started to taper, but the artist still feels 200 euros (doubled from 100) is worth paying. At the point where sales drop to a level that the ever increasing renewel cost is more than the profit made in a year, the artist is encouraged to produce a new work, if they haven't already.
2) A news broadcast or article. No need to register because it would take too long, but they are only covered for a month. After that, registration is required to renew. The financial potential of news works diminishes rapidly, and it is in the public interest that it falls into the public domain equally quickly so that it can be discused, analysed, and derived into secondary works without limit as soon as possible.
3) A film. Production costs are high, and the chances of becoming a classic are low, so we would have a long period for films, say 5 years, which should be enough to recoup the production costs and make a profit. If it isn't, then film was likely a commercial failure anyway. 5 years should be enough time to determine whether a film has any value as a so called cult-classic in the era of digital distribution and social media. Renewal costs for films start at 10,000 euro though because the term is so long.
In each of these examples, the length of the copyright is regulated by the perceived value (where entertainment is also considered valueable) of the individual work by society at large. This also encourages rights holders to make their works as widey available as possible in the shortest amount of time possible, and makes rent-seeking behaviours un-profitable very quickly. Finally, it ensures long term availability by making sure the work fall into the public domain as soon as the rights holder no longer deems it profitable, which is exactly how long copyrights should last.