We want to add a prefix to the ffmpeg log message, so we called mp_msg
multiple times until now. But logging such partial lines is a race
condition, because there's only one internal mp_msg buffer, and no
external mp_msg locks.
Avoid this by building the message on a stack buffer.
I might make a mp_log-local partial line buffer, but even then av_log()
can be called from multiple threads, while targetting the same mp_log.
(Really, ffmpeg's log API needs to be fixed.)
The complex filter support that will be added makes much more complex
use of libavfilter, and I'm not going to bother with adding hacks to
keep libavfilter optional.
This happens with av_log(NULL, ...) calls. Drop the "?: " fallback
prefix, because it was confusing.
(Of course FFmpeg should not do this at all, but it's a very long way to
making the FFmpeg log callback sane.)
This is slightly "dangerous", because it could overwrite a log callback
another library has set, after we've set our own callback. But it's
probably still slightly better than leaving our own callback, which will
run the fallback code if no mpv instance is set. (Multiple mpv instances
sharing the same global state will safely avoid overwriting each other's
log callback.)
Note that we can't do much better, because the global state in FFmpeg is
obviously insane.
The code in main.c calls exit() explicitly, but the code is actually
easier to follow by simply exiting from main() instead. The exit() call
in av_log.c happens only on severely broken builds, so replace it with
abort().
(Shuts up rpmlint warnings.)
Print a warning if a library has mismatched compile time and link time
versions.
Refuse to work if the compile time and link time versions are a mix of
ffmpeg and libav. We print an error message and call exit(). Since we'd
randomly crash anyway, I think this is ok.
This doesn't catch the case if you e.g. use a ffmpeg libavcodec and a
libav libavformat, which would of course just crash as quickly, but I
think this checks enough already.
This is pretty nasty, because FFmpeg/Libav is yet another library with a
global message callback. We do something with mutexes trying to get it
done, but of course we can't actually solve this problem. If more than
one library in a process use FFmpeg/Libav, only one of them will get log
messages.
Always pass around mp_log contexts in the option parser code. This of
course affects all users of this API as well.
In stream.c, pass a mp_null_log, because we can't do it properly yet.
This will be fixed later.
