flac encoders: use the long format extradata

fLaC marker is helpful for file format detection

modules/codec/avcodec/encoder.c

@@ -822,16 +822,41 @@ int OpenEncoder( vlc_object_t *p_this )
 
     av_dict_free(&options);
 
-    p_enc->fmt_out.i_extra = p_context->extradata_size;
-    if( p_enc->fmt_out.i_extra )
+    if( i_codec_id == AV_CODEC_ID_FLAC )
     {
+        p_enc->fmt_out.i_extra = 4 + 1 + 3 + p_context->extradata_size;
         p_enc->fmt_out.p_extra = malloc( p_enc->fmt_out.i_extra );
-        if ( p_enc->fmt_out.p_extra == NULL )
+        if( p_enc->fmt_out.p_extra )
         {
-            goto error;
+            uint8_t *p = p_enc->fmt_out.p_extra;
+            p[0] = 0x66;    /* f */
+            p[1] = 0x4C;    /* L */
+            p[2] = 0x61;    /* a */
+            p[3] = 0x43;    /* C */
+            p[4] = 0x80;    /* streaminfo block, last block before audio */
+            p[5] = ( p_context->extradata_size >> 16 ) & 0xff;
+            p[6] = ( p_context->extradata_size >>  8 ) & 0xff;
+            p[7] = ( p_context->extradata_size       ) & 0xff;
+            memcpy( &p[8], p_context->extradata, p_context->extradata_size );
+        }
+        else
+        {
+            p_enc->fmt_out.i_extra = 0;
+        }
+    }
+    else
+    {
+        p_enc->fmt_out.i_extra = p_context->extradata_size;
+        if( p_enc->fmt_out.i_extra )
+        {
+            p_enc->fmt_out.p_extra = malloc( p_enc->fmt_out.i_extra );
+            if ( p_enc->fmt_out.p_extra == NULL )
+            {
+                goto error;
+            }
+            memcpy( p_enc->fmt_out.p_extra, p_context->extradata,
+                    p_enc->fmt_out.i_extra );
         }
-        memcpy( p_enc->fmt_out.p_extra, p_context->extradata,
-                p_enc->fmt_out.i_extra );
     }
 
     p_context->flags &= ~CODEC_FLAG_GLOBAL_HEADER;

modules/codec/flac.c

@@ -584,9 +584,12 @@ EncoderWriteCallback( const FLAC__StreamEncoder *encoder,
             msg_Dbg( p_enc, "Writing STREAMINFO: %zu", bytes );
 
             /* Backup the STREAMINFO metadata block */
-            p_enc->fmt_out.i_extra = STREAMINFO_SIZE;
-            p_enc->fmt_out.p_extra = xmalloc( STREAMINFO_SIZE );
-            memcpy(p_enc->fmt_out.p_extra, buffer + 4, STREAMINFO_SIZE );
+            p_enc->fmt_out.i_extra = STREAMINFO_SIZE + 8;
+            p_enc->fmt_out.p_extra = xmalloc( STREAMINFO_SIZE + 8);
+            memcpy(p_enc->fmt_out.p_extra, "fLaC", 4);
+            memcpy(p_enc->fmt_out.p_extra + 4, buffer, STREAMINFO_SIZE );
+            /* Fake this as the last metadata block */
+            ((uint8_t*)p_enc->fmt_out.p_extra)[4] |= 0x80;
         }
         p_sys->i_headers++;
         return FLAC__STREAM_DECODER_WRITE_STATUS_CONTINUE;