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avcodec/mpegvideo_enc: Don't use unnecessarily much stack

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encode_thread() puts two MPVEncContexts (2*6516B here)
on the stack and zeroes one of them in order to
temporarily store the variables that get changed
during encoding a macroblock (when there is more than
one candidate type for a macroblock). This is wasteful
and therefore this commit adds a small (328B here) structure
to store exactly the fields that actually need to be backed
up. Then one can extend MPVEncContext without fearing
too use up to much stack.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
This commit is contained in:
Andreas Rheinhardt
2025-03-25 18:00:25 +01:00
parent f8360ed629
commit 074d8343d6
1 changed files with 88 additions and 68 deletions
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156
libavcodec/mpegvideo_enc.c
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@ -2632,80 +2632,100 @@ static void encode_mb(MPVEncContext *const s, int motion_x, int motion_y)
encode_mb_internal(s, motion_x, motion_y, 16, 16, 12, 0, 0, CHROMA_444);
}
static inline void copy_context_before_encode(MPVEncContext *const d,
const MPVEncContext *const s)
{
int i;
typedef struct MBBackup {
struct {
int mv[2][4][2];
int last_mv[2][2][2];
int mv_type, mv_dir;
int last_dc[3];
int mb_intra, mb_skipped, mb_skip_run;
int qscale;
int block_last_index[8];
int interlaced_dct;
int16_t (*block)[64];
} c;
int mv_bits, i_tex_bits, p_tex_bits, i_count, misc_bits, last_bits;
int dquant;
int esc3_level_length;
PutBitContext pb, pb2, tex_pb;
} MBBackup;
memcpy(d->c.last_mv, s->c.last_mv, 2*2*2*sizeof(int)); //FIXME is memcpy faster than a loop?
/* MPEG-1 */
d->c.mb_skip_run = s->c.mb_skip_run;
for(i=0; i<3; i++)
d->c.last_dc[i] = s->c.last_dc[i];
/* statistics */
d->mv_bits= s->mv_bits;
d->i_tex_bits= s->i_tex_bits;
d->p_tex_bits= s->p_tex_bits;
d->i_count= s->i_count;
d->misc_bits= s->misc_bits;
d->last_bits= 0;
d->c.mb_skipped = 0;
d->c.qscale = s->c.qscale;
d->dquant= s->dquant;
d->esc3_level_length= s->esc3_level_length;
#define COPY_CONTEXT(BEFORE, AFTER, DST_TYPE, SRC_TYPE) \
static inline void BEFORE ##_context_before_encode(DST_TYPE *const d, \
const SRC_TYPE *const s) \
{ \
/* FIXME is memcpy faster than a loop? */ \
memcpy(d->c.last_mv, s->c.last_mv, 2*2*2*sizeof(int)); \
\
/* MPEG-1 */ \
d->c.mb_skip_run = s->c.mb_skip_run; \
for (int i = 0; i < 3; i++) \
d->c.last_dc[i] = s->c.last_dc[i]; \
\
/* statistics */ \
d->mv_bits = s->mv_bits; \
d->i_tex_bits = s->i_tex_bits; \
d->p_tex_bits = s->p_tex_bits; \
d->i_count = s->i_count; \
d->misc_bits = s->misc_bits; \
d->last_bits = 0; \
\
d->c.mb_skipped = 0; \
d->c.qscale = s->c.qscale; \
d->dquant = s->dquant; \
\
d->esc3_level_length = s->esc3_level_length; \
} \
\
static inline void AFTER ## _context_after_encode(DST_TYPE *const d, \
const SRC_TYPE *const s, \
int data_partitioning) \
{ \
/* FIXME is memcpy faster than a loop? */ \
memcpy(d->c.mv, s->c.mv, 2*4*2*sizeof(int)); \
memcpy(d->c.last_mv, s->c.last_mv, 2*2*2*sizeof(int)); \
\
/* MPEG-1 */ \
d->c.mb_skip_run = s->c.mb_skip_run; \
for (int i = 0; i < 3; i++) \
d->c.last_dc[i] = s->c.last_dc[i]; \
\
/* statistics */ \
d->mv_bits = s->mv_bits; \
d->i_tex_bits = s->i_tex_bits; \
d->p_tex_bits = s->p_tex_bits; \
d->i_count = s->i_count; \
d->misc_bits = s->misc_bits; \
\
d->c.mb_intra = s->c.mb_intra; \
d->c.mb_skipped = s->c.mb_skipped; \
d->c.mv_type = s->c.mv_type; \
d->c.mv_dir = s->c.mv_dir; \
d->pb = s->pb; \
if (data_partitioning) { \
d->pb2 = s->pb2; \
d->tex_pb = s->tex_pb; \
} \
d->c.block = s->c.block; \
for (int i = 0; i < 8; i++) \
d->c.block_last_index[i] = s->c.block_last_index[i]; \
d->c.interlaced_dct = s->c.interlaced_dct; \
d->c.qscale = s->c.qscale; \
\
d->esc3_level_length = s->esc3_level_length; \
}
static inline void copy_context_after_encode(MPVEncContext *const d,
const MPVEncContext *const s,
int data_partitioning)
{
int i;
COPY_CONTEXT(backup, save, MBBackup, MPVEncContext)
COPY_CONTEXT(reset, store, MPVEncContext, MBBackup)
memcpy(d->c.mv, s->c.mv, 2*4*2*sizeof(int));
memcpy(d->c.last_mv, s->c.last_mv, 2*2*2*sizeof(int)); //FIXME is memcpy faster than a loop?
/* MPEG-1 */
d->c.mb_skip_run = s->c.mb_skip_run;
for(i=0; i<3; i++)
d->c.last_dc[i] = s->c.last_dc[i];
/* statistics */
d->mv_bits= s->mv_bits;
d->i_tex_bits= s->i_tex_bits;
d->p_tex_bits= s->p_tex_bits;
d->i_count= s->i_count;
d->misc_bits= s->misc_bits;
d->c.mb_intra = s->c.mb_intra;
d->c.mb_skipped = s->c.mb_skipped;
d->c.mv_type = s->c.mv_type;
d->c.mv_dir = s->c.mv_dir;
d->pb= s->pb;
if (data_partitioning) {
d->pb2= s->pb2;
d->tex_pb= s->tex_pb;
}
d->c.block = s->c.block;
for(i=0; i<8; i++)
d->c.block_last_index[i] = s->c.block_last_index[i];
d->c.interlaced_dct = s->c.interlaced_dct;
d->c.qscale = s->c.qscale;
d->esc3_level_length= s->esc3_level_length;
}
static void encode_mb_hq(MPVEncContext *const s, MPVEncContext *const backup, MPVEncContext *const best,
static void encode_mb_hq(MPVEncContext *const s, MBBackup *const backup, MBBackup *const best,
PutBitContext pb[2], PutBitContext pb2[2], PutBitContext tex_pb[2],
int *dmin, int *next_block, int motion_x, int motion_y)
{
int score;
uint8_t *dest_backup[3];
copy_context_before_encode(s, backup);
reset_context_before_encode(s, backup);
s->c.block = s->c.blocks[*next_block];
s->pb = pb[*next_block];
@ -2745,7 +2765,7 @@ static void encode_mb_hq(MPVEncContext *const s, MPVEncContext *const backup, MP
*dmin= score;
*next_block^=1;
copy_context_after_encode(best, s, s->c.data_partitioning);
save_context_after_encode(best, s, s->c.data_partitioning);
}
}
@ -2963,7 +2983,7 @@ static int encode_thread(AVCodecContext *c, void *arg){
MPVEncContext *const s = *(void**)arg;
int chr_h = 16 >> s->c.chroma_y_shift;
int i;
MPVEncContext best_s = { 0 }, backup_s;
MBBackup best_s = { 0 }, backup_s;
uint8_t bit_buf[2][MAX_MB_BYTES];
uint8_t bit_buf2[2][MAX_MB_BYTES];
uint8_t bit_buf_tex[2][MAX_MB_BYTES];
@ -3164,7 +3184,7 @@ static int encode_thread(AVCodecContext *c, void *arg){
int next_block=0;
int pb_bits_count, pb2_bits_count, tex_pb_bits_count;
copy_context_before_encode(&backup_s, s);
backup_context_before_encode(&backup_s, s);
backup_s.pb= s->pb;
if (s->c.data_partitioning) {
backup_s.pb2= s->pb2;
@ -3389,7 +3409,7 @@ static int encode_thread(AVCodecContext *c, void *arg){
}
}
copy_context_after_encode(s, &best_s, s->c.data_partitioning);
store_context_after_encode(s, &best_s, s->c.data_partitioning);
pb_bits_count= put_bits_count(&s->pb);
flush_put_bits(&s->pb);