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audio: work around ffmpeg being a piece of shit

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The "amultiply" filter crashes in AVX mode on unaligned access if an
audio pointer is unaligned (on 32 or 64 bytes I assume).

A requirement that audio data needs to be aligned isn't documented
anywhere. In our case, the data is still sample- and channel-aligned,
which is completely sane. Sure, you can imagine optimizations which make
some algorithms even faster by requiring higher alignment. But, and this
is a big but, you shouldn't crash api users because you just invented a
new undocumented requirement. And even more importantly, your
user-crashing optimization won't matter because it's just a trivial
algorithm working on audio. You don't need to pretend to be an
optimization devil, and nobody will give you a prize for this. But no,
lets random make API users crash (and then probably blame them for it!)
for something that wouldn't matter at all.

Not to mention that they do "document" some requirements on _video_
data, yet their vf_crop probably can still produce unaligned video
pointers. Oh how hilarious that the same documentation also talks about
libswscale alignment requirements. (This is weird because libswscale is
just one of many, many things which consume video data. Also did you
know that zimg, written in C++ and using intrinsics, i.e. the antithesis
to FFmpeg development, is much faster than libswscale, easier to use,
and produces more correct results, even if you ignore that libswscale
flat out doesn't support some very important features?)

Fucking tired of this bullshit. Can't wait until someone comes up with a
better framework than this... (well let's not write this out).

Fix this by copying instead of adjusting the start pointer when skipping
samples. This makes general operations slower just to fix interoperating
with a single filter. Thank you for your "optimization", FFmpeg. Go die
in a fire.

Didn't check whether this is correct. It probably is? If the frame needs
to be copied (due to COW), and memory allocation fails, it just silently
(or audibly lol) doesn't skip samples, because a never-fail function can
suddenly fail. Well, who cares.

Fixes: #7141
This commit is contained in:
wm4 2019-11-10 15:02:25 +01:00
parent 35de8ea0a8
commit 4667b3a182
1 changed files with 8 additions and 2 deletions
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10
audio/aframe.c
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@ -410,10 +410,16 @@ void mp_aframe_skip_samples(struct mp_aframe *f, int samples)
{
assert(samples >= 0 && samples <= mp_aframe_get_size(f));
if (av_frame_make_writable(f->av_frame) < 0)
return; // go complain to ffmpeg
int num_planes = mp_aframe_get_planes(f);
size_t sstride = mp_aframe_get_sstride(f);
for (int n = 0; n < num_planes; n++)
f->av_frame->extended_data[n] += samples * sstride;
for (int n = 0; n < num_planes; n++) {
memmove(f->av_frame->extended_data[n],
f->av_frame->extended_data[n] + samples * sstride,
(f->av_frame->nb_samples - samples) * sstride);
}
f->av_frame->nb_samples -= samples;