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avcodec/h261enc: Fix ac_vlc_length tables

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These tables are supposed to contain the number of bits needed
to encode a given (run, level) pair. Yet the number of bits
for pairs needing the escape code was wrong (it only contained
the escape code and not the bits needed for run and level).

Furthermore, H.261 (a format with explicit end-of-block codes)
does not work well together with the RLTable API from rl.c:
The EOB code is the first one in ff_h261_rl_tcoeff's VLC table
and has a run value of zero. Therefore the result of get_rl_index()
is off by one for run == 0 and level values with explicit
(run, level) pair.

Fixing this necessitated changing the ref files of the
vsynth*-h261-trellis tests. Both filesizes as well as PSNR
decreased. If one used a qscale value of 11 for this test,
one would have received files with about the same size as
before this patch (with qscale 12), but with better PSNR.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
This commit is contained in:
Andreas Rheinhardt 2024-06-15 18:44:18 +02:00
parent f3829cc72d
commit 3a5202d026
4 changed files with 24 additions and 59 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

59
libavcodec/h261enc.c
View File

@ -38,14 +38,15 @@
#define H261_MAX_RUN 26
#define H261_MAX_LEVEL 15
#define H261_ESC_LEN (6 + 6 + 8)
static struct VLCLUT {
uint8_t len;
uint16_t code;
} vlc_lut[H261_MAX_RUN + 1][32 /* 0..2 * H261_MAX_LEN are used */];
static uint8_t uni_h261_rl_len [64*64*2*2];
#define UNI_ENC_INDEX(last,run,level) ((last)*128*64 + (run)*128 + (level))
static uint8_t uni_h261_rl_len [64 * 128];
static uint8_t uni_h261_rl_len_last[64 * 128];
typedef struct H261EncContext {
MpegEncContext s;
@ -320,51 +321,10 @@ void ff_h261_encode_mb(MpegEncContext *s, int16_t block[6][64],
}
}
static av_cold void init_uni_h261_rl_tab(const RLTable *rl, uint8_t *len_tab)
{
int slevel, run, last;
av_assert0(MAX_LEVEL >= 64);
av_assert0(MAX_RUN >= 63);
for(slevel=-64; slevel<64; slevel++){
if(slevel==0) continue;
for(run=0; run<64; run++){
for(last=0; last<=1; last++){
const int index= UNI_ENC_INDEX(last, run, slevel+64);
int level= slevel < 0 ? -slevel : slevel;
int len, code;
len_tab[index]= 100;
/* ESC0 */
code= get_rl_index(rl, 0, run, level);
len= rl->table_vlc[code][1] + 1;
if(last)
len += 2;
if(code!=rl->n && len < len_tab[index]){
len_tab [index]= len;
}
/* ESC */
len = rl->table_vlc[rl->n][1];
if(last)
len += 2;
if(len < len_tab[index]){
len_tab [index]= len;
}
}
}
}
}
static av_cold void h261_encode_init_static(void)
{
static uint8_t h261_rl_table_store[2][2 * MAX_RUN + MAX_LEVEL + 3];
ff_rl_init(&ff_h261_rl_tcoeff, h261_rl_table_store);
init_uni_h261_rl_tab(&ff_h261_rl_tcoeff, uni_h261_rl_len);
memset(uni_h261_rl_len, H261_ESC_LEN, sizeof(uni_h261_rl_len));
memset(uni_h261_rl_len_last, H261_ESC_LEN + 2 /* EOB */, sizeof(uni_h261_rl_len_last));
// The following loop is over the ordinary elements, not EOB or escape.
for (size_t i = 1; i < FF_ARRAY_ELEMS(ff_h261_tcoeff_vlc) - 1; i++) {
@ -375,6 +335,11 @@ static av_cold void h261_encode_init_static(void)
vlc_lut[run][H261_MAX_LEVEL + level] = (struct VLCLUT){ len, code << 1 };
vlc_lut[run][H261_MAX_LEVEL - level] = (struct VLCLUT){ len, (code << 1) | 1 };
uni_h261_rl_len [UNI_AC_ENC_INDEX(run, 64 + level)] = len;
uni_h261_rl_len [UNI_AC_ENC_INDEX(run, 64 - level)] = len;
uni_h261_rl_len_last[UNI_AC_ENC_INDEX(run, 64 + level)] = len + 2;
uni_h261_rl_len_last[UNI_AC_ENC_INDEX(run, 64 - level)] = len + 2;
}
}
@ -398,10 +363,10 @@ av_cold int ff_h261_encode_init(MpegEncContext *s)
s->min_qcoeff = -127;
s->max_qcoeff = 127;
s->ac_esc_length = 6+6+8;
s->ac_esc_length = H261_ESC_LEN;
s->intra_ac_vlc_length = s->inter_ac_vlc_length = uni_h261_rl_len;
s->intra_ac_vlc_last_length = s->inter_ac_vlc_last_length = uni_h261_rl_len + 128*64;
s->intra_ac_vlc_last_length = s->inter_ac_vlc_last_length = uni_h261_rl_len_last;
ff_thread_once(&init_static_once, h261_encode_init_static);
return 0;

8
tests/ref/vsynth/vsynth1-h261-trellis
View File

@ -1,4 +1,4 @@
02b4109ce5343b7ef24fb11c2635498a *tests/data/fate/vsynth1-h261-trellis.avi
655416 tests/data/fate/vsynth1-h261-trellis.avi
70ceba944548ba680b1101c91707ea25 *tests/data/fate/vsynth1-h261-trellis.out.rawvideo
stddev: 8.75 PSNR: 29.28 MAXDIFF: 90 bytes: 7603200/ 7603200
9980463214cb744a7780737a16408540 *tests/data/fate/vsynth1-h261-trellis.avi
590384 tests/data/fate/vsynth1-h261-trellis.avi
7bbb0520a5ca26cdcea148f9997eae27 *tests/data/fate/vsynth1-h261-trellis.out.rawvideo
stddev: 9.09 PSNR: 28.96 MAXDIFF: 93 bytes: 7603200/ 7603200

8
tests/ref/vsynth/vsynth2-h261-trellis
View File

@ -1,4 +1,4 @@
f5e0cfc70bbe4f4048c15be88dea4378 *tests/data/fate/vsynth2-h261-trellis.avi
249856 tests/data/fate/vsynth2-h261-trellis.avi
15452237f6c333690d3e05f354f63196 *tests/data/fate/vsynth2-h261-trellis.out.rawvideo
stddev: 7.10 PSNR: 31.10 MAXDIFF: 96 bytes: 7603200/ 7603200
cdf6013013b8de3fe56476178b5adc89 *tests/data/fate/vsynth2-h261-trellis.avi
227156 tests/data/fate/vsynth2-h261-trellis.avi
d1107f161a7d923e0ffb6aeb9c713633 *tests/data/fate/vsynth2-h261-trellis.out.rawvideo
stddev: 7.24 PSNR: 30.93 MAXDIFF: 87 bytes: 7603200/ 7603200

8
tests/ref/vsynth/vsynth_lena-h261-trellis
View File

@ -1,4 +1,4 @@
41522be50f14b7fff6b1fb8d10b1ff00 *tests/data/fate/vsynth_lena-h261-trellis.avi
184586 tests/data/fate/vsynth_lena-h261-trellis.avi
f9df8cd110a2f3d9706dd2f29a1d0a89 *tests/data/fate/vsynth_lena-h261-trellis.out.rawvideo
stddev: 6.32 PSNR: 32.11 MAXDIFF: 89 bytes: 7603200/ 7603200
aa3e00ffeb48a23452bb1c5b0dde9e77 *tests/data/fate/vsynth_lena-h261-trellis.avi
167808 tests/data/fate/vsynth_lena-h261-trellis.avi
055f8805df2bb21ef6752dc944e7828d *tests/data/fate/vsynth_lena-h261-trellis.out.rawvideo
stddev: 6.43 PSNR: 31.96 MAXDIFF: 87 bytes: 7603200/ 7603200