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Old 2nd December 2013, 02:42   #181  |  Link
SirLagsalot
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Quote:
Originally Posted by LoRd_MuldeR
Well, as long as the encoder and the decoder need to do this step in the exactly same way, things could go still go wrong and break decoding, right?
No, the code and the inputs are identical, so the output will be identical as long as the same floating-point state (rounding mode and precision) are used.

Quote:
Originally Posted by LoRd_MuldeR
Hmm, to my knowledge there's at least the classical "x87" FPU with 80-Bit internal precision and the newer SIMD (MMX, SSE, etc) instructions with "only" 64-Bit precision. Even if all variables are 64-Bit (double) precision in memory, the compiler may still keep intermediate results in registers, which would then be either 80-Bit or 64-Bit. Furthermore, even if you don't use SIMD assembly/intrinsic explicitly, compilers may still generate such instructions when targeting CPU's with MMX/SSE support. Finally, there are various compiler settings that effect floating point math ("fast math" option, etc). So there's at least the danger of "portability" issues when the encoder/decoder are compiled with different compilers (compiler configuration).
Lagarith uses the 53-bit precision mode for floating point, so none of those variations in potential precision end up affecting the result. It also checks and sets the floating point state if need be, so even if Lagarith was compiled with the wrong settings by someone else, it would be corrected at run-time.
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Old 4th December 2013, 04:35   #182  |  Link
ChiDragon
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Originally Posted by SirLagsalot View Post
Sure, I can check if it is using the full bit-depth.
Here you go, a VHS sample. Possibly not all that useful for you: WinRAR gave it a steady 51% compression, so I'm guessing it is 9-bit. That would also make sense because a guy opened up the next model in this line of AV syncs and found a Philips SAA7113 was the ADC.
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Old 4th December 2013, 11:21   #183  |  Link
zerowalker
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So wait, does Lagarith not have the problem and just some people, or are you talking about something else (Lagalot?)
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Old 5th December 2013, 00:25   #184  |  Link
SirLagsalot
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Zerowalker, I think early on some people were seeing glitches from other causes and assuming it was due to floating point math errors; and then the rumor stuck around long after the actual bugs were fixed.
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Old 9th December 2013, 13:09   #185  |  Link
zerowalker
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Oh, well letīs hope thatīs the case, really like the codec and some fundamental error like that would really ruin it.
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Old 26th May 2014, 22:17   #186  |  Link
zerowalker
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It seems the "Floating Point" errors actually does exist, at least from my understanding in my discussion with an ffmpeg developer.

Not entirely sure, but if am understand things correctly, in normal circumstances the errors shouldn't appear.
But if it's not an x86 system it will, though that doesn't tell me much, as i am sure x64 is still an x86 system;S

Quote:
The original codec implementation uses floating point arithmetic which will fail on processors != x86 and might fail if you use another compiler. FFmpeg's implementation is fixed-point (which is what you expect for a lossless codec) meaning you can compile it for any hardware with any (non-broken) C compiler and you will always get correct (bitexact) output. Fixed-point arithmetic is often slower than floating-point on typical hardware.
See also (for example):
https://lists.ffmpeg.org/pipermail/f...er/079680.html
http://mod16.org/hurfdurf/?p=142

I personally have never seen any corrupt frames that i can think of, and i have been using Lagarith quite a bit, so i think i should have encountered it by now.
Though again, that depends what a "corrupt frame" is, if it's 1 pixel that's wrong, then it's not possible i have noticed it, but if it's an entire corrupted imaged, that's another story.
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Old 4th March 2015, 22:34   #187  |  Link
Kein
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Anyone by any chance has some speed stats mt LAGS 1.3.27 vs Huffyuv?
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Old 4th March 2015, 22:45   #188  |  Link
poisondeathray
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Anyone by any chance has some speed stats mt LAGS 1.3.27 vs Huffyuv?
http://forum.doom9.org/showthread.ph...92#post1668292
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