Re: [FFmpeg-devel] [PATCH 3/7] avfilter/vf_framerate: factorize blend_frames

[Marton Balint]

On Wed, 3 Jan 2018, Michael Niedermayer wrote:

On Wed, Jan 03, 2018 at 08:00:24PM +0100, Marton Balint wrote:


On Wed, 3 Jan 2018, Marton Balint wrote:


On Tue, 2 Jan 2018, Michael Niedermayer wrote:

On Sun, Dec 10, 2017 at 11:11:18PM +0100, Marton Balint wrote:
Signed-off-by: Marton Balint <c...@passwd.hu>
---
libavfilter/vf_framerate.c | 54
++++++----------------------------------------
1 file changed, 7 insertions(+), 47 deletions(-)

This broke fate-filter-framerate-up on x86-32 (gcc 4.8 (Ubuntu
4.8.5-2ubuntu1~14.04.1))

--- tests/ref/fate/filter-framerate-up  2017-12-31 19:27:30.039451874
+0100
+++ tests/data/fate/filter-framerate-up 2018-01-02 02:12:56.151674862
+0100
@@ -4,12 +4,12 @@
#dimensions 0: 320x240
#sar 0: 1/1
0,          0,          0,        1,   115200, 0x3744b3ed
-0,          1,          1,        1,   115200, 0xc44bdc65
-0,          2,          2,        1,   115200, 0xa17f0d74
-0,          3,          3,        1,   115200, 0xb0c83274
-0,          4,          4,        1,   115200, 0x232d6368
+0,          1,          1,        1,   115200, 0x3744b3ed
+0,          2,          2,        1,   115200, 0x3744b3ed
+0,          3,          3,        1,   115200, 0x3744b3ed
+0,          4,          4,        1,   115200, 0x6e318ba0
0,          5,          5,        1,   115200, 0x6e318ba0
-0,          6,          6,        1,   115200, 0x247e846e
-0,          7,          7,        1,   115200, 0x89e27599
-0,          8,          8,        1,   115200, 0x31c5704e
-0,          9,          9,        1,   115200, 0x97e45fec
+0,          6,          6,        1,   115200, 0x6e318ba0
+0,          7,          7,        1,   115200, 0x6e318ba0
+0,          8,          8,        1,   115200, 0x6e318ba0
+0,          9,          9,        1,   115200, 0x48d65876
Test filter-framerate-up failed. Look at
tests/data/fate/filter-framerate-up.err for details.
make: *** [fate-filter-framerate-up] Error 1

in master the diff now looks like this:
--- tests/ref/fate/filter-framerate-up  2017-12-31 19:27:30.039451874
+0100
+++ tests/data/fate/filter-framerate-up 2018-01-02 02:42:46.103712572
+0100
@@ -4,12 +4,12 @@
#dimensions 0: 320x240
#sar 0: 1/1
0,          0,          0,        1,   115200, 0x3744b3ed
-0,          1,          1,        1,   115200, 0xc44bdc65
+0,          1,          1,        1,   115200, 0x3744b3ed
0,          2,          2,        1,   115200, 0xa17f0d74
0,          3,          3,        1,   115200, 0xb0c83274
0,          4,          4,        1,   115200, 0x232d6368
0,          5,          5,        1,   115200, 0x6e318ba0
-0,          6,          6,        1,   115200, 0x247e846e
+0,          6,          6,        1,   115200, 0x6e318ba0
0,          7,          7,        1,   115200, 0x89e27599
0,          8,          8,        1,   115200, 0x31c5704e
0,          9,          9,        1,   115200, 0x97e45fec
Test filter-framerate-up failed. Look at
tests/data/fate/filter-framerate-up.err for details.
make: *** [fate-filter-framerate-up] Error 1

Does not happen if compiled with -O1 or -O0. With -O2 and -O3
fabsf(intepolate) becomes NaN.

I am guessing that some floating point state is lost because of the SAD
MMX instructions, but I don't know if this is a compiler bug or something
should be done differently.

Do you have an idea how to proceeed?

I guess I will just commit the patch which eliminates the floating point
calculations, that should fix this failure as well.

yes, less fpu is better.

ive not had time to look so its a far fetched guess,
maybe something is exactly between 2 integers rounding wise and that gets
sent to different sides on different platforms

I don't think so, as my debugging showed NaN values for 
fabsf(interpolate), so this does not look like a simple rouding error, 
but some strange FPU state corruption.

In any case, integer math will solve it.

Regards,
Marton
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