diff -uNrp a/common/common.c b/common/common.c
--- a/common/common.c	2010-02-24 10:20:41 +0200
+++ b/common/common.c	2010-03-03 19:33:57 +0200
@@ -259,7 +259,7 @@ static int x264_param_apply_preset( x264
     }
     else
     {
-        fprintf( stderr, "x264 [error]: invalid preset '%s'\n", preset );
+        x264_log( NULL, X264_LOG_ERROR, "invalid preset '%s'\n", preset );
         return -1;
     }
     return 0;
@@ -345,14 +345,14 @@ static int x264_param_apply_tune( x264_p
         }
         else
         {
-            fprintf( stderr, "x264 [error]: invalid tune '%s'\n", s );
+            x264_log( NULL, X264_LOG_ERROR, "invalid tune '%s'\n", s );
             x264_free( tmp );
             return -1;
         }
         if( 0 )
         {
     psy_failure:
-            fprintf( stderr, "x264 [warning]: only 1 psy tuning can be used: ignoring tune %s\n", s );
+            x264_log( NULL, X264_LOG_WARNING, "only 1 psy tuning can be used: ignoring tune %s\n", s );
         }
         s = strtok( NULL, ",./-+" );
     }
@@ -399,7 +399,7 @@ int x264_param_apply_profile( x264_param
         param->analyse.i_weighted_pred = X264_WEIGHTP_NONE;
         if( param->b_interlaced )
         {
-            fprintf( stderr, "x264 [error]: baseline profile doesn't support interlacing\n" );
+            x264_log( NULL, X264_LOG_ERROR, "baseline profile doesn't support interlacing\n" );
             return -1;
         }
     }
@@ -414,13 +414,13 @@ int x264_param_apply_profile( x264_param
     }
     else
     {
-        fprintf( stderr, "x264 [error]: invalid profile: %s\n", profile );
+        x264_log( NULL, X264_LOG_ERROR, "invalid profile: %s\n", profile );
         return -1;
     }
     if( (param->rc.i_rc_method == X264_RC_CQP && param->rc.i_qp_constant == 0) ||
         (param->rc.i_rc_method == X264_RC_CRF && param->rc.f_rf_constant == 0) )
     {
-        fprintf( stderr, "x264 [error]: %s profile doesn't support lossless\n", profile );
+        x264_log( NULL, X264_LOG_ERROR, "%s profile doesn't support lossless\n", profile );
         return -1;
     }
     return 0;
diff -uNrp a/common/cpu.c b/common/cpu.c
--- a/common/cpu.c	2010-02-15 12:48:41 +0200
+++ b/common/cpu.c	2010-03-03 19:33:57 +0200
@@ -213,7 +213,7 @@ uint32_t x264_cpu_detect( void )
         else if( cache == 64 )
             cpu |= X264_CPU_CACHELINE_64;
         else
-            fprintf( stderr, "x264 [warning]: unable to determine cacheline size\n" );
+            x264_log( NULL, X264_LOG_WARNING, "unable to determine cacheline size\n" );
     }
 
 #ifdef BROKEN_STACK_ALIGNMENT
diff -uNrp a/common/macroblock.c b/common/macroblock.c
--- a/common/macroblock.c	2010-02-28 13:25:46 +0200
+++ b/common/macroblock.c	2010-03-03 19:38:56 +0200
@@ -291,7 +291,7 @@ static int x264_mb_predict_mv_direct16x1
           || mv[1][1] > h->mb.mv_max_spel[1] ) )
     {
 #if 0
-        fprintf(stderr, "direct_spatial: (%d,%d) (%d,%d) > %d \n",
+        x264_log( h, X264_LOG_DEBUG, "direct_spatial: (%d,%d) (%d,%d) > %d \n",
                 mv[0][0], mv[0][1], mv[1][0], mv[1][1],
                 h->mb.mv_max_spel[1]);
 #endif
diff -uNrp a/encoder/analyse.c b/encoder/analyse.c
--- a/encoder/analyse.c	2010-02-28 13:25:46 +0200
+++ b/encoder/analyse.c	2010-03-03 19:39:49 +0200
@@ -3204,13 +3204,13 @@ static void x264_analyse_update_cache( x
             if( (h->mb.cache.mv[l][x264_scan8[15]][1] >> (2 - h->mb.b_interlaced)) + h->mb.i_mb_y*16 > completed )
             {
                 x264_log( h, X264_LOG_WARNING, "internal error (MV out of thread range)\n");
-                fprintf(stderr, "mb type: %d \n", h->mb.i_type);
-                fprintf(stderr, "mv: l%dr%d (%d,%d) \n", l, ref,
+                x264_log( h, X264_LOG_DEBUG, "mb type: %d \n", h->mb.i_type);
+                x264_log( h, X264_LOG_DEBUG, "mv: l%dr%d (%d,%d) \n", l, ref,
                                 h->mb.cache.mv[l][x264_scan8[15]][0],
                                 h->mb.cache.mv[l][x264_scan8[15]][1] );
-                fprintf(stderr, "limit: %d \n", h->mb.mv_max_spel[1]);
-                fprintf(stderr, "mb_xy: %d,%d \n", h->mb.i_mb_x, h->mb.i_mb_y);
-                fprintf(stderr, "completed: %d \n", completed );
+                x264_log( h, X264_LOG_DEBUG, "limit: %d \n", h->mb.mv_max_spel[1]);
+                x264_log( h, X264_LOG_DEBUG, "mb_xy: %d,%d \n", h->mb.i_mb_x, h->mb.i_mb_y);
+                x264_log( h, X264_LOG_DEBUG, "completed: %d \n", completed );
                 x264_log( h, X264_LOG_WARNING, "recovering by using intra mode\n");
                 x264_mb_analyse_intra( h, a, COST_MAX );
                 h->mb.i_type = I_16x16;