x264: write first SEI NAL into first picture

It contains the x264 version info and options used for encoding
If we let it in extradata it will not be present in the final file

libavcodec does that already, and this makes it easier to compare x264
options used by VLC and FFmpeg.

Comparing FFmpeg and VLC with the exact same set of options might help
finding why mpeg (at least mpeg2/mpeg4/flv) encoding is 5 times slower
with vlc than with ffmpeg, supposedly for the same set of options.

modules/codec/x264.c

@@ -42,6 +42,8 @@
 #endif
 #include <x264.h>
 
+#include <assert.h>
+
 #define SOUT_CFG_PREFIX "sout-x264-"
 
 /*****************************************************************************
@@ -712,6 +714,8 @@ struct encoder_sys_t
     mtime_t         i_initial_delay;
 
     char            *psz_stat_name;
+    int             i_sei_size;
+    uint8_t         *p_sei;
 };
 
 #ifdef PTW32_STATIC_LIB
@@ -753,6 +757,8 @@ static int  Open ( vlc_object_t *p_this )
         return VLC_ENOMEM;
     p_sys->i_initial_delay = 0;
     p_sys->psz_stat_name = NULL;
+    p_sys->i_sei_size = 0;
+    p_sys->p_sei = NULL;
 
     x264_param_default( &p_sys->param );
     char *psz_preset = var_GetString( p_enc, SOUT_CFG_PREFIX  "preset" );
@@ -1260,19 +1266,42 @@ static int  Open ( vlc_object_t *p_this )
     }
 
     /* get the globals headers */
-    p_enc->fmt_out.i_extra = x264_encoder_headers( p_sys->h, &nal, &i_nal );
-    p_enc->fmt_out.p_extra = malloc( p_enc->fmt_out.i_extra );
-    if( !p_enc->fmt_out.p_extra )
+    size_t i_extra = x264_encoder_headers( p_sys->h, &nal, &i_nal );
+    uint8_t *p_extra = p_enc->fmt_out.p_extra = malloc( i_extra );
+    if( !p_extra )
     {
         Close( VLC_OBJECT(p_enc) );
         return VLC_ENOMEM;
     }
-    uint8_t *p_tmp = p_enc->fmt_out.p_extra;
+
     for( i = 0; i < i_nal; i++ )
     {
-        memcpy( p_tmp, nal[i].p_payload, nal[i].i_payload );
-        p_tmp += nal[i].i_payload;
+        if( nal[i].i_type != NAL_SEI )
+        {
+            memcpy( p_extra, nal[i].p_payload, nal[i].i_payload );
+            p_extra += nal[i].i_payload;
+            continue; /* next NAL */
+        }
+
+        /* we won't store this NAL in p_extra */
+        assert( i_extra >= (size_t)nal[i].i_payload );
+        i_extra -= nal[i].i_payload;
+
+        /* Make sure we only have one SEI NAL in the headers */
+        assert(p_sys->i_sei_size == 0);
+        p_sys->i_sei_size = nal[i].i_payload;
+
+        p_sys->p_sei = malloc( p_sys->i_sei_size );
+        if( !p_sys->p_sei )
+        {
+            free( p_extra );
+            Close( VLC_OBJECT(p_enc) );
+            return VLC_ENOMEM;
         }
+        memcpy( p_sys->p_sei, nal[i].p_payload, nal[i].i_payload );
+    }
+
+    p_enc->fmt_out.i_extra = i_extra;
 
     return VLC_SUCCESS;
 }
@@ -1321,7 +1350,8 @@ static block_t *Encode( encoder_t *p_enc, picture_t *p_pict )
 
 
     /* Get size of block we need */
-    for( i = 0, i_out = 0; i < i_nal; i++ )
+    i_out = p_sys->i_sei_size;
+    for( i = 0; i < i_nal; i++ )
         i_out += nal[i].i_payload;
 
     p_block = block_New( p_enc, i_out );
@@ -1330,6 +1360,15 @@ static block_t *Encode( encoder_t *p_enc, picture_t *p_pict )
     /* copy encoded data directly to block */
     for( i = 0, i_out = 0; i < i_nal; i++ )
     {
+        if( p_sys->i_sei_size && nal[i].i_type == NAL_SLICE )
+        {
+            /* insert x264 headers SEI nal before first SLICE nal */
+            memcpy( p_block->p_buffer, p_sys->p_sei, p_sys->i_sei_size );
+            i_out += p_sys->i_sei_size;
+            p_sys->i_sei_size = 0;
+            free( p_sys->p_sei );
+            p_sys->p_sei = NULL;
+        }
         memcpy( p_block->p_buffer + i_out, nal[i].p_payload, nal[i].i_payload );
         i_out += nal[i].i_payload;
     }
@@ -1364,6 +1403,7 @@ static void Close( vlc_object_t *p_this )
     encoder_sys_t *p_sys = p_enc->p_sys;
 
     free( p_sys->psz_stat_name );
+    free( p_sys->p_sei );
 
     msg_Dbg( p_enc, "framecount still in libx264 buffer: %d", x264_encoder_delayed_frames( p_sys->h ) );