Kostya's Boring Codec World

Yes, it’s about FFmpeg and Libav again. And yes, I consider them both to be failed projects (not that their basic goal is failed and they provide even less multimedia support than GStreamer with no external libraries used), I mean the state of the project as living and developing entity.

Even if I mostly emulate Derek nowadays—i.e. unsubscribed from FFmpeg and Libav mailing lists, do nothing productive, wait for somebody to reverse engineer codecs I care about somewhat (that would be ClearVideo, thank you very much). Yet I peruse development-related resources for both projects (mostly for finding laughs) and sometimes I see gems like this (it was pointed at in the comments as well since it answers some questions I’ve asked before).

First, I’d like to outline how large projects are organised and what to expect in general. So, if you have a large and used project you’ll have at least these components:

• codebase (normal projects have some code to run after all);
• developers (to add features, fix bugs and such);
• users (to annoy developers and once in a while to provide sensible bugreport or feature request);
• infrastructure (hosting for code, means to communicate for developers, maybe even support for users).

Developers can be also divided into three main categories:

1. core developers—the ones who do main work on the codebase and do it in regular manner (they might intersect with the next category too);
2. corporate developers—the ones who do work mostly on behalf of their companies (e.g. add a feature they need internally so they don’t have to maintain it themselves);
3. contributors—developers who add some feature or provide some bugfix because they needed it themselves, they do it irregularly or even just once (again, they might intersect with the previous category).

This division is by no means perfect but it shows the main forces behind development: those who treat is as a hobby, those who do it for their benefit (i.e. making money with/from it) and those who use it and just want to be it a bit more suited to their personal needs.

So, with that all in mind let’s look at the projects:

FFmpeg

Codebase. It’s a complete mess. And its git history is even worse. The running joke is that who cares what that piece of code does, it’s FFeature so it must be kept at whatever cost (that’s how you get double decoders, demuxers and encoders; an outstanding example there would be libutvideo wrappers—refer for the details to ffmpeg-devel mailing list).

Developers. Because of the merging policy (that is likely to be codified soon—see this document again) many developers of FFmpeg code are not FFmpeg developers. And yet they are dictating API to be used in FFmpeg: the first example that also involves me—I’ve proposed side data for packets in Libav, FFmpeg hesitated for a bit yet included it with such flattering message; the most of examples include Anton’s work from introducing refcounted buffers to splitting codec parameters into separate structure—in any case FFmpeg simply takes it and converts their code to comply with a new practice (even if it has to include some horrible hacks). If that doesn’t cry out loud “a failed project” I don’t know what does.

Also (even if I’m stepping onto minefield) some FFmpeg developers are completely unfit for collective work because of their personal qualities. People may make jokes about providing full console output of ffmpeg command but it’s not Carl who’s the main problem in FFmpeg (yes, people who didn’t work on MPlayer might think otherwise; I still believe he’d be a decent leader for FFmpeg—mostly because he doesn’t focus just on technical side and he’s unlikely to be treated as a technical god who can’t make any mistake or write less than perfect code). Here it’s more about Michael and Clément—the former never really understood what being a leader really is or what resigning from a leader means (anyone disagreeing please ban yourself from a mailing list of your choice for 24 hours), the latter does not understand people at all (neither does Michael)—I’m not going to paste the link to the same document for the third time, I’ll simply quote the relevant part:

Any Libav developer is of course welcome anytime to contribute directly to the
FFmpeg tree. Of course, we fully understand and are forced to accept that very
few Libav developers are interested in doing so, but we still want to recognize
their work.

Here’s an excerpt from Michael’s mail:

> Don’t you think you should remove Diego, Måns, Kostya, … as well?

They didnt ask me to remove them, they didnt remove themselfs even
though they could, they didnt post a patch to remove themselfs.
No contributor said that he contacted them and they no longer maintain
the code they are listed for. (or i missed that)

Well, if it’s hard to realize that Libav developers don’t want to contribute to FFmpeg and don’t want to do anything with it even though it’s been over five years then you really have a problem. And I’ve expressed my thought on reuniting both projects already.

Users. You know, there’s a difference between catering to your users and selling out completely (to put it mildly). When you see some changes being done in interests of some third party often without mentioning it that looks suspicious. I’m not against making money off your work but when it’s not even mentioning the fact it looks strange; when you have a decoder with a copyright assigned to some company it’s fine, but when you have fixes for files nobody has seen or FFv1 features added because it was all paid by somebody (see here slide 12) it looks not completely honest even if there’s nothing wrong with it.

Infrastructure. From what I understood FFmpeg services are now hosted on various boxes with no plan or idea (i.e. if somebody could provide a box for something they took it) and there’s no system administrator for these boxes. Again, as I understand it, they were kicked out of Hungary for some reason and even though they got a free server and hosting in Bulgaria they cannot use that box properly because there’s nobody to set it up properly and maintain afterwards. Sounds like fail to me.

Libav

This project is failed for the different reasons but failed nevertheless.

Codebase. While it’s mostly fine sadly new features hardly come in. Just two examples—there have been talks about replacing libswscale since ages, two years ago they’d started to design it (and it went nowhere), then I offered my design with a PoC (yes, piece of that) code to test it (that’s how NAScale was born), people work on integrating it into Libav a bit and that’s all—nothing has happened yet; the second example is bitstream reader replacement—since its submission in April nothing has come out of it as all traction was lost in bikeshedding. Is it failure or what?

Developers. Here we have two problems—some FFmpeg folks and some core developers. I’ve written about the former before so let’s talk about the latter. Surprisingly or not there are counterparts for Austrian FFmpeg developers in Libav. Where in FFmpeg you have Carl Eugen, in Libav there’s Diego and I guess many have suffered from his perfectionism (in form of proper formatting). And instead of Michael there’s Anton. While he is not that leadery in general sense, he’s the one introducing big changes in API that are hardly discussed before. And even worse thing—he tries to make all nontrivial code go through him, QSV support is a good example: Maxym Dmytrychenko had submitted initial support but it was not deemed good enough so Luca Barbato had to rework it into proper form. And what do you know? It turned out to be not good enough for Anton so he worked on it himself with the result not being much different from Luca’s. And since nothing is being done about that I consider it to be a failure.

Users. Sadly, there seems to exist not so many of them which is a fail. On the other hoof they don’t need to deal with distros and Baidu and that’s a blessing by itself. Though there is still an issue with FFmpeg users who bother (ex-)developers for features present in FFmpeg but not in Libav (or present in different form), like Blackmagic card support or prores_ks encoder (hint: there’s no encoder with such name in Libav and it’s my personal pleasure to ignore mails about it).

Infrastructure. From what I heard thanks to Attila and Janne everything is working fine.

Well, maybe I should continue with Actimagine VX codec at last and forget about multimedia outside work matters afterwards (insert the obvious joke about this not hurting NihAV development at all).

Disclaimer: the word “schizophrenia” is used here as it’s perceived by majority, not to denote a certain psychological condition. Feel free to be offended.

I’ve wasted about a decade working at two multimedia projects (plus a patch or two to unrelated projects) and what I’ve seen there leads me to the conclusion they both suffer from schizophrenia, albeit in different forms.

FFmpeg

FFmpeg features two forms of schizophrenia—developers and code.

Developers schizophrenia can be seen in how some developers believe they are also Libav developers. Mostly they brag because they’ve sent a patch or two to Libav and now can use it as a free review service. While I dislike Carl Eugen he’s at least honest and acts to his beliefs (here, an amended Elenril’s Law fulfilled; in case you’ve forgotten it says “Every FFmpeg-related discussion ends up mentioning Michael. Or Carl Eugen.”).

Code schizophrenia is more celebrated. The most prominent example is ProRes support—they offer two decoders and two encoders for it. There are two ASF demuxers as well. And two audio resampling libraries. And there are talks about adding second libswscale (*shudder*). The best part is that if you ask why it will probably go like this:

— Why do you have feature X in two versions?
— Because Libav has it.
— But why do you take it if you have your own version?
— To make merging Libav codebase easier.
— But why do you need to merge it at all?
— To make merging Libav codebase easier.

Please please tell me I’m wrong and provide proper reasons why FFmpeg keeps merging Libav stuff and keeps several versions of the same feature.

Libav

Here it’s somewhat more interesting—you have developers with physical multiple personalities disorder. Unlike the case in FFmpeg here you have people that work solely on Libav but as several different people. Most prominent examples are Luca (known as lu_zero and koda on IRC) who is really several instances not always agreeing with themselves (and if you subscribe to Lu_zianism then he’s also both Michael and Carl Eugen too, if you don’t believe it—you should because it annoys him/them). And there’s also Alexandra (aka beta elenril) and Anton (aka sasshka 2.0). And that’s the majority of core Libav developers anyway.

But at least the project seems to be more happy with itself and probably has a dream similar to the Ukrainian dream (which is “bugger off you damned Russians” in case you didn’t know).

It was somewhat fun to watch the fate of proposed bitstream reader replacement. Alexandra (she’s also Top Libav Blogger ?2 by the way—simply because she blogs) proposed a new bitstream reader to replace the old horror (which is a good idea), and that new bitstream reader turned out to be faster than the old mess too, and what was the result? If I’d be British I’d call it sheep-worrying.

Those developers from FFmpeg that believe they also should have a say in Libav process started to express their opinions. While there were independent benchmarking proving the new implementation is indeed faster (which is a good thing to provide) those benchmarks were also run on the decoder not present in Libav, with badly converted functions for code reading, and that turned out to have some problems because of the encoder used (also not in Libav) that produced nonconforming stream and screwed multi-threaded decoding benchmarks (that one can be seen as both trollish and arrogant—kinda like judging The Beatles performance from an excerpt sung by your not very talented neighbour).

But mostly it was bikeshedding and asking why it was not using old get_bits interface. The answer for the latter is simple—because it was built from horrible macros used in half of the places directly so you should either to make everything follow those macros design or convert the old UPDATE_CACHE(); LAST_SKIP_BITS(); ... CLOSE_READER(); into saner get_bits(); skip_bits(); anyway. And Libav developers decided it’s better to have fully new interface anyway and to make it consistent with bytestream reading while at it.

So why did people who should have nothing to do with it bikeshedded that much? Probably because they know in their hearts that as soon as it hits Libav the work on copying it into FFmpeg starts and sooner or later it will reside in FFmpeg codebase probably along with old get_bits.h with most decoders switched to the new bitstream reader anyway. Why? See the theoretical conversation above. I’d like to know the answer why merges are really done but I guess I’ll get it no sooner than this bitstream reader is accepted into Libav master (i.e. never).