diff --git a/common/common.c b/common/common.c
index 84bf49f..907a7b8 100644
--- a/common/common.c
+++ b/common/common.c
@@ -88,6 +88,7 @@ void    x264_param_default( x264_param_t *param )
     param->rc.f_vbv_buffer_init = 0.9;
     param->rc.i_qp_constant = 23;
     param->rc.f_rf_constant = 23;
+    param->rc.f_cssim = 0.98;
     param->rc.i_qp_min = 10;
     param->rc.i_qp_max = 51;
     param->rc.i_qp_step = 4;
@@ -529,6 +530,11 @@ int x264_param_parse( x264_param_t *p, const char *name, const char *value )
         p->rc.f_rf_constant = atof(value);
         p->rc.i_rc_method = X264_RC_CRF;
     }
+    OPT("cssim")
+    {
+        p->rc.f_cssim = atof(value);
+        p->rc.i_rc_method = X264_RC_CSSIM;
+    }
     OPT("rc-lookahead")
         p->rc.i_lookahead = atoi(value);
     OPT2("qpmin", "qp-min")
@@ -870,6 +876,7 @@ char *x264_param2string( x264_param_t *p, int b_res )
 
     s += sprintf( s, " rc=%s mbtree=%d", p->rc.i_rc_method == X264_RC_ABR ?
                                ( p->rc.b_stat_read ? "2pass" : p->rc.i_vbv_buffer_size ? "cbr" : "abr" )
+                               : p->rc.i_rc_method == X264_RC_CSSIM ? "cssim"
                                : p->rc.i_rc_method == X264_RC_CRF ? "crf" : "cqp", p->rc.b_mb_tree );
     if( p->rc.i_rc_method == X264_RC_ABR || p->rc.i_rc_method == X264_RC_CRF )
     {
@@ -889,14 +896,19 @@ char *x264_param2string( x264_param_t *p, int b_res )
     }
     else if( p->rc.i_rc_method == X264_RC_CQP )
         s += sprintf( s, " qp=%d", p->rc.i_qp_constant );
+    else if( p->rc.i_rc_method == X264_RC_CSSIM )
+        s += sprintf( s, " cssim=%.7f qpmin=%d qpmax=%d", p->rc.f_cssim, p->rc.i_qp_min, p->rc.i_qp_max );
     if( !(p->rc.i_rc_method == X264_RC_CQP && p->rc.i_qp_constant == 0) )
     {
-        s += sprintf( s, " ip_ratio=%.2f", p->rc.f_ip_factor );
-        if( p->i_bframe && !p->rc.b_mb_tree )
-            s += sprintf( s, " pb_ratio=%.2f", p->rc.f_pb_factor );
-        s += sprintf( s, " aq=%d", p->rc.i_aq_mode );
-        if( p->rc.i_aq_mode )
-            s += sprintf( s, ":%.2f", p->rc.f_aq_strength );
+        if( p->rc.i_rc_method != X264_RC_CSSIM )
+        {
+            s += sprintf( s, " ip_ratio=%.2f", p->rc.f_ip_factor );
+            if( p->i_bframe && !p->rc.b_mb_tree )
+                s += sprintf( s, " pb_ratio=%.2f", p->rc.f_pb_factor );
+            s += sprintf( s, " aq=%d", p->rc.i_aq_mode );
+            if( p->rc.i_aq_mode )
+                s += sprintf( s, ":%.2f", p->rc.f_aq_strength );
+        }
         if( p->rc.psz_zones )
             s += sprintf( s, " zones=%s", p->rc.psz_zones );
         else if( p->rc.i_zones )
diff --git a/common/macroblock.c b/common/macroblock.c
index 0a9f31e..58d320b 100644
--- a/common/macroblock.c
+++ b/common/macroblock.c
@@ -740,7 +740,7 @@ int x264_macroblock_cache_init( x264_t *h )
     h->mb.i_neighbour8[3] = MB_LEFT|MB_TOP|MB_TOPLEFT;
 
     int buf_hpel = (h->param.i_width+48) * sizeof(int16_t);
-    int buf_ssim = h->param.analyse.b_ssim * 8 * (h->param.i_width/4+3) * sizeof(int);
+    int buf_ssim = (h->param.analyse.b_ssim || h->param.rc.i_rc_method == X264_RC_CSSIM) * 8 * (h->param.i_width/4+3) * sizeof(int);
     int me_range = X264_MIN(h->param.analyse.i_me_range, h->param.analyse.i_mv_range);
     int buf_tesa = (h->param.analyse.i_me_method >= X264_ME_ESA) *
         ((me_range*2+18) * sizeof(int16_t) + (me_range+4) * (me_range+1) * 4 * sizeof(mvsad_t));
diff --git a/encoder/analyse.c b/encoder/analyse.c
index 44a8a50..3bc173a 100644
--- a/encoder/analyse.c
+++ b/encoder/analyse.c
@@ -2192,6 +2192,45 @@ static inline void x264_mb_analyse_transform_rd( x264_t *h, x264_mb_analysis_t *
     }
 }
 
+static void x264_rc_constant_ssim( x264_t *h )
+{
+    int bak_trellis = h->mb.b_trellis;
+    int qp = h->mb.i_qp, bqp = h->mb.i_qp;
+    int prev_dir = 0;
+    float bdssim, tssim;
+
+    x264_emms();
+    bdssim = 2.0*9.0;
+    tssim = h->param.rc.f_cssim * 9.0;
+    h->mb.b_trellis = 0;
+
+    while( qp >= h->param.rc.i_qp_min && qp <= h->param.rc.i_qp_max )
+    {
+        float ssim, dssim;
+        int dir;
+        h->mb.i_type = I_16x16;
+        h->mb.b_transform_8x8 = 0;
+        h->mb.i_qp = qp;
+        h->mb.i_chroma_qp = h->chroma_qp_table[h->mb.i_qp];
+        x264_macroblock_encode( h );
+        x264_emms();
+        ssim = x264_pixel_ssim_wxh( &h->pixf, h->mb.pic.p_fenc[0], FENC_STRIDE, h->mb.pic.p_fdec[0], FDEC_STRIDE, 16, 16, h->scratch_buffer );
+        dssim = fabs(ssim - tssim);
+        COPY2_IF_LT( bdssim, dssim, bqp, qp );
+        dir = ssim < tssim ? -1 : 1;
+        if( dir * prev_dir < 0 )
+            break;
+        if( dir == 1 && !h->mb.cbp[h->mb.i_mb_xy] )
+            break;
+        qp += dir;
+        prev_dir = dir;
+    }
+
+    h->mb.i_qp = bqp;
+    h->mb.i_chroma_qp = h->chroma_qp_table[h->mb.i_qp];
+    h->mb.b_trellis = bak_trellis;
+}
+
 /* Rate-distortion optimal QP selection.
  * FIXME: More than half of the benefit of this function seems to be
  * in the way it improves the coding of chroma DC (by decimating or
@@ -2275,6 +2314,12 @@ int x264_macroblock_analyse( x264_t *h )
 
     x264_mb_analyse_init( h, &analysis, h->mb.i_qp );
 
+    if( h->param.rc.i_rc_method == X264_RC_CSSIM )
+    {
+        x264_rc_constant_ssim( h );
+        x264_mb_analyse_init( h, &analysis, h->mb.i_qp );
+    }
+
     /*--------------------------- Do the analysis ---------------------------*/
     if( h->sh.i_type == SLICE_TYPE_I )
     {
diff --git a/encoder/encoder.c b/encoder/encoder.c
index 6d28d09..6f33279 100644
--- a/encoder/encoder.c
+++ b/encoder/encoder.c
@@ -409,11 +409,12 @@ static int x264_validate_parameters( x264_t *h )
         }
     }
 
-    if( h->param.rc.i_rc_method < 0 || h->param.rc.i_rc_method > 2 )
+    if( h->param.rc.i_rc_method < 0 || h->param.rc.i_rc_method > 3 )
     {
         x264_log( h, X264_LOG_ERROR, "no ratecontrol method specified\n" );
         return -1;
     }
+    h->param.rc.f_cssim = x264_clip3f( h->param.rc.f_cssim, 0.0, 1.0 );
     h->param.rc.f_rf_constant = x264_clip3f( h->param.rc.f_rf_constant, 0, 51 );
     h->param.rc.i_qp_constant = x264_clip3( h->param.rc.i_qp_constant, 0, 51 );
     if( h->param.rc.i_rc_method == X264_RC_CRF )
@@ -452,6 +453,14 @@ static int x264_validate_parameters( x264_t *h )
         h->param.rc.i_aq_mode = 0;
         h->param.rc.b_mb_tree = 0;
     }
+    if( h->param.rc.i_rc_method == X264_RC_CSSIM )
+    {
+        h->param.rc.f_rf_constant = 26.f;
+        h->param.rc.i_qp_constant = 26;
+        h->param.rc.b_mb_tree = 0;
+        h->param.rc.f_ip_factor = 1;
+        h->param.rc.f_pb_factor = 1;
+    }
     h->param.rc.i_qp_max = x264_clip3( h->param.rc.i_qp_max, 0, 51 );
     h->param.rc.i_qp_min = x264_clip3( h->param.rc.i_qp_min, 0, h->param.rc.i_qp_max );
 
@@ -570,8 +579,8 @@ static int x264_validate_parameters( x264_t *h )
     h->param.rc.f_aq_strength = x264_clip3f( h->param.rc.f_aq_strength, 0, 3 );
     if( h->param.rc.f_aq_strength == 0 )
         h->param.rc.i_aq_mode = 0;
-    /* MB-tree requires AQ to be on, even if the strength is zero. */
-    if( !h->param.rc.i_aq_mode && h->param.rc.b_mb_tree )
+    /* MB-tree or CSSIM requires AQ to be on, even if the strength is zero. */
+    if( (!h->param.rc.i_aq_mode && h->param.rc.b_mb_tree) || (h->param.rc.i_rc_method == X264_RC_CSSIM) )
     {
         h->param.rc.i_aq_mode = 1;
         h->param.rc.f_aq_strength = 0;
@@ -770,6 +779,7 @@ x264_t *x264_encoder_open   ( x264_param_t *param )
     h->frames.b_have_lowres = !h->param.rc.b_stat_read
         && ( h->param.rc.i_rc_method == X264_RC_ABR
           || h->param.rc.i_rc_method == X264_RC_CRF
+          || h->param.rc.i_rc_method == X264_RC_CSSIM
           || h->param.i_bframe_adaptive
           || h->param.i_scenecut_threshold
           || h->param.rc.b_mb_tree );
@@ -826,8 +836,9 @@ x264_t *x264_encoder_open   ( x264_param_t *param )
 
     h->out.i_nal = 0;
     h->out.i_bitstream = X264_MAX( 1000000, h->param.i_width * h->param.i_height * 4
-        * ( h->param.rc.i_rc_method == X264_RC_ABR ? pow( 0.95, h->param.rc.i_qp_min )
-          : pow( 0.95, h->param.rc.i_qp_constant ) * X264_MAX( 1, h->param.rc.f_ip_factor )));
+        * ((h->param.rc.i_rc_method == X264_RC_ABR || h->param.rc.i_rc_method == X264_RC_CSSIM)
+           ? pow( 0.95, h->param.rc.i_qp_min )
+           : pow( 0.95, h->param.rc.i_qp_constant ) * X264_MAX( 1, h->param.rc.f_ip_factor )));
 
     h->thread[0] = h;
     h->i_thread_num = 0;
diff --git a/encoder/ratecontrol.c b/encoder/ratecontrol.c
index 47491d9..bcebdf5 100644
--- a/encoder/ratecontrol.c
+++ b/encoder/ratecontrol.c
@@ -322,7 +322,7 @@ int x264_ratecontrol_new( x264_t *h )
     CHECKED_MALLOCZERO( h->rc, h->param.i_threads * sizeof(x264_ratecontrol_t) );
     rc = h->rc;
 
-    rc->b_abr = h->param.rc.i_rc_method != X264_RC_CQP && !h->param.rc.b_stat_read;
+    rc->b_abr = (h->param.rc.i_rc_method != X264_RC_CQP && h->param.rc.i_rc_method != X264_RC_CSSIM) && !h->param.rc.b_stat_read;
     rc->b_2pass = h->param.rc.i_rc_method == X264_RC_ABR && h->param.rc.b_stat_read;
 
     /* FIXME: use integers */
@@ -345,16 +345,16 @@ int x264_ratecontrol_new( x264_t *h )
     rc->last_non_b_pict_type = -1;
     rc->cbr_decay = 1.0;
 
-    if( h->param.rc.i_rc_method == X264_RC_CRF && h->param.rc.b_stat_read )
+    if( h->param.rc.i_rc_method != X264_RC_ABR && h->param.rc.b_stat_read )
     {
-        x264_log(h, X264_LOG_ERROR, "constant rate-factor is incompatible with 2pass.\n");
+        x264_log(h, X264_LOG_ERROR, "Non-ABR rate control is incompatible with 2pass.\n");
         return -1;
     }
     if( h->param.rc.i_vbv_buffer_size )
     {
-        if( h->param.rc.i_rc_method == X264_RC_CQP )
+        if( h->param.rc.i_rc_method == X264_RC_CQP || h->param.rc.i_rc_method == X264_RC_CSSIM )
         {
-            x264_log(h, X264_LOG_WARNING, "VBV is incompatible with constant QP, ignored.\n");
+            x264_log(h, X264_LOG_WARNING, "VBV is incompatible with constant %s, ignored.\n", h->param.rc.i_rc_method == X264_RC_CQP ? "QP" : "SSIM");
             h->param.rc.i_vbv_max_bitrate = 0;
             h->param.rc.i_vbv_buffer_size = 0;
         }
diff --git a/x264.c b/x264.c
index 32e6570..25c49c3 100644
--- a/x264.c
+++ b/x264.c
@@ -203,6 +203,7 @@ static void Help( x264_param_t *defaults, int b_longhelp )
     H0( "  -q, --qp <integer>          Set QP (0-51, 0=lossless)\n" );
     H0( "  -B, --bitrate <integer>     Set bitrate (kbit/s)\n" );
     H0( "      --crf <float>           Quality-based VBR (0-51, 0=lossless) [%.1f]\n", defaults->rc.f_rf_constant );
+    H1( "      --cssim <float>         Force all macroblocks to this SSIM\n" );
     H0( "      --rc-lookahead <integer> Number of frames for frametype lookahead [%d]\n", defaults->rc.i_lookahead );
     H0( "      --vbv-maxrate <integer> Max local bitrate (kbit/s) [%d]\n", defaults->rc.i_vbv_max_bitrate );
     H0( "      --vbv-bufsize <integer> Set size of the VBV buffer (kbit) [%d]\n", defaults->rc.i_vbv_buffer_size );
@@ -406,6 +407,7 @@ static struct option long_options[] =
     { "qpmax",       required_argument, NULL, 0 },
     { "qpstep",      required_argument, NULL, 0 },
     { "crf",         required_argument, NULL, 0 },
+    { "cssim",       required_argument, NULL, 0 },
     { "rc-lookahead",required_argument, NULL, 0 },
     { "ref",         required_argument, NULL, 'r' },
     { "asm",         required_argument, NULL, 0 },
diff --git a/x264.h b/x264.h
index 964e093..b525512 100644
--- a/x264.h
+++ b/x264.h
@@ -86,6 +86,7 @@ typedef struct x264_t x264_t;
 #define X264_RC_CQP                  0
 #define X264_RC_CRF                  1
 #define X264_RC_ABR                  2
+#define X264_RC_CSSIM                3
 #define X264_AQ_NONE                 0
 #define X264_AQ_VARIANCE             1
 #define X264_AQ_AUTOVARIANCE         2
@@ -263,6 +264,7 @@ typedef struct x264_param_t
 
         int         i_bitrate;
         float       f_rf_constant;  /* 1pass VBR, nominal QP */
+        float       f_cssim;
         float       f_rate_tolerance;
         int         i_vbv_max_bitrate;
         int         i_vbv_buffer_size;