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 features two forms of schizophreniaâ€”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 supportâ€”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:
â€” Why do you have feature X in two versions?
â€” Because Libav has it.
â€” But why do you take it if you have your own version?
â€” To make merging Libav codebase easier.
â€” But why do you need to merge it at all?
â€” 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.
Here it’s somewhat more interestingâ€”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
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 itâ€”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 â„–2 by the wayâ€”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 arrogantâ€”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 simpleâ€”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).