Relicensing VLC from GPL to LGPL

LWN.net needs you!

Without subscribers, LWN would simply not exist. Please consider signing up for a subscription and helping to keep LWN publishing.

Select a software license can be tricky, considering all of the effects that such a choice has for the future: library compatibility, distribution, even membership in larger projects. But agreeing on a license at the beginning is child's play compared to trying to alter that decision later on. Case in point: the VLC media player has recently been relicensed under LGPLv2.1+, an undertaking that required project lead Jean-Baptiste Kempf to track down more than 230 individual developers for their personal authorization for the move.

VLC had been licensed under GPLv2+ since 2001; the development team decided to undertake the relicensing task for a number of reasons, including making VLC compatible with various gadget-vendor application stores (e.g., Apple's). Making the core engine available under LGPL terms would make it a more attractive target for independent developers seeking to write non-GPL applications, the argument goes, which benefits the project through added exposure, and may even attract additional contributor talent.

The license migration was approved by team vote in September 2011. The first big milestone was cleared the following November, a relicensing of libVLC and libVLCcore (which implement the external API and internal plugin layer, respectively), plus the auxiliary libraries libdvbpsi, libaacs, and libbluray. Kempf described the process involved on his blog. Because VLC contributors retain the authors' rights to their contributions, no matter how small, Kempf needed to locate and obtain permission from all of the roughly 150 developers who had written even a minor patch during the project's long history.

To do so, he harvested names and email addresses from the project's git repository and logs, and undertook a lengthy process of sifting through the records (both to weed out false matches, and to identify contributors who were credited in unofficial spots like in-line comments). With the list in hand, Kempf set out to contact each of the contributors to approve the licensing change. He was ultimately successful, and the change was committed. The commit notes that more than 99% of the developers consented to the change, and those agreeing account for 99.99% of the code, which he said is sufficient from a legal standpoint.

The modular community

But, as Kempf described in a follow-up post, the same method was less successful when he set out in 2012 to relicense the next major chunk of VLC code: the major playback modules. Together, they constitute a much larger codebase, with considerably more contributors (including some who are not necessarily committed VLC team members). After emailing the module authors, he said, he received responses from only 25% of them. Two rounds of follow-up emails edged the number up closer to 50%, but for the remainder he resorted to "finding and stalking" the holdouts through other means. Those means included IRC, GitHub, social networks, mutual friends, employers, and even whois data on domain names.

In the end, he managed to get approval from the overwhelming majority of the contributors, but there were some "no"s as well, plus a handful of individuals who never replied at all. At that point, he had to examine the unresolved contributions themselves and decide whether to delete them, reimplement them, refactor them into separate files, or drop the offending modules altogether. He made the license-changing commit on November 6, and listed about 25 modules that were not included. They include the work of 13 developers who either declined give their approval or were unreachable, plus a set of modules that were ports from other projects (such as Xine or MPlayer) and thus not in the VLC team's purview.

By all accounts, the legwork required to hunt down and cajole more than 230 developers was arduous: in the second blog post, Kempf noted that it could get "really annoying" to contact people "over, over, over and over, and over" to ask for an answer. That is probably an understatement; in an email Kempf said at the outset that no one thought it would even be doable.

He also elaborated on what comes next. Not every VLC module was targeted for the relicensing work of the previous year, he said. Out of the roughly 400 modules being developed, about 100 remain non-LGPL. First, for those who rarely venture beyond VLC's desktop media player functionality, it can be easy to forget all of the other functions it provides; those modules will remain under their existing licenses. In particular, VLC's media server, converter, and proxy functionality will remain in GPL modules. Other modules, including scripting and visualization, will remain GPL-licensed at least for the time being, because they do not impede the ability of third-party developers to write non-GPL playback applications, which was the leading use-case motivating the change. VLC's user interface and control modules will also remain GPL-licensed, in order to discourage non-free forks.

Kempf also pointed out that the VideoLAN non-profit organization holds the trademarks to VLC, VideoLAN, and other names, and restricts their usage to open source code. That reflects the project's concern that the move away from the GPL will be misinterpreted by someone as a move away from free-ness (in multiple senses of the word); in addition to the trademark policy, both of the announcements about the relicensing project have emphasized that despite the change, VLC will remain free software.

Holdouts

But despite the consensus reached by the majority of core and module developers, there is still the problem of those twenty-odd playback modules that, for one reason or another, are not being relicensed. Kempf explained that the main VLC application will still be able to use all of the non-LGPL modules, and that only third-party libVLC applications will encounter any difficulties with license compatibility.

Authors of such applications may write their own modules for the missing functionality, or simply migrate to another module — given the modular nature of VLC, there are several modules out there that duplicate functionality implemented elsewhere. "The results might be slightly different, but I doubt many people will notice. There are a few exceptions, (probably 2 or 3) that will get rewritten, at some point, I think."

There are two modules Kempf predicted will never be reimplemented in LGPL code — DVD playback and Teletext support — because they rely on other GPL-licensed packages without viable non-GPL alternatives. He still holds out hope for tracking down a few of the still-unreached contributors, of course — only the authors of the iOS, Dolby, Headphone, and Mono modules outright declined to relicense their work.

It is not possible to predict exactly what effect the LGPL-relicensing work will have on third-party developers targeting iOS or other "app store" markets, thanks to the often opaque processes governing which content gets in and which gets rejected. But VLC was yanked from the iOS App Store in January 2011, a decision believed to be due to the GPL license. But because Apple does not provide details about its decisions, the situation remains nebulous.

Nevertheless, hunting down several hundred individual developers from more than a decade of development is an impressive feat of, shall we say, logistical engineering. Relicensing a community project is rarely a simple task; one is reminded of the multi-year process required to relicense the Heyu home automation engine, which involved tracking down the estates of developers no longer with us. Many large software projects have contemplated a license change at one time or another, and typically the scope of tracking down and persuading all of the former developers is cited as a reason that such a change is unworkable. For example, VLC's contributor pool is far smaller than the kernel's, to be sure. But the fact that Kempf was able to successfully chase down virtually the full set of both uncooperative and unintentionally-AWOL contributors in such a short time frame is an admirable achievement. Then again, the VLC team has long enjoyed a reputation for admirable achievements.