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a2d3511154
Currently, the decoder checks the 128th value of the 4th quant table during
while deriving the context on each sample, in order to speed itself up. This
is due to relying on the behavior of FFmpeg's FFV1 encoder, in which if that
value is zero, the entire 4th and 5th quant tables are assumed to be entirely
zero.
This does not match the FFV1 spec, which has no such restriction, and after
some discussion, it was decided to fix FFmpeg to abide by the spec, rather
than change the spec.
We will now check whether the 4th and 5th quant tables are zero properly,
by checking the 128th valye of both tables (which means they are zero due
to the way they're coded in the bitstream).
For further context, the FFV1 issue in question is located at:
https://github.com/FFmpeg/FFV1/issues/169
Signed-off-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>
54 lines
1.8 KiB
C
54 lines
1.8 KiB
C
/*
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* FFV1 codec
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*
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* Copyright (c) 2003-2013 Michael Niedermayer <michaelni@gmx.at>
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*
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* This file is part of FFmpeg.
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*
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* FFmpeg is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 2.1 of the License, or (at your option) any later version.
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*
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* FFmpeg is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with FFmpeg; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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*/
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static inline int RENAME(predict)(TYPE *src, TYPE *last)
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{
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const int LT = last[-1];
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const int T = last[0];
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const int L = src[-1];
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return mid_pred(L, L + T - LT, T);
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}
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static inline int RENAME(get_context)(PlaneContext *p, TYPE *src,
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TYPE *last, TYPE *last2)
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{
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const int LT = last[-1];
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const int T = last[0];
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const int RT = last[1];
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const int L = src[-1];
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if (p->quant_table[3][127] || p->quant_table[4][127]) {
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const int TT = last2[0];
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const int LL = src[-2];
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return p->quant_table[0][(L - LT) & 0xFF] +
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p->quant_table[1][(LT - T) & 0xFF] +
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p->quant_table[2][(T - RT) & 0xFF] +
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p->quant_table[3][(LL - L) & 0xFF] +
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p->quant_table[4][(TT - T) & 0xFF];
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} else
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return p->quant_table[0][(L - LT) & 0xFF] +
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p->quant_table[1][(LT - T) & 0xFF] +
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p->quant_table[2][(T - RT) & 0xFF];
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}
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