refine the librtmp, open writer then reader.

@@ -473,22 +473,22 @@ srs_flv_t srs_flv_open(const char* file)
     
     FlvContext* flv = new FlvContext();
     
-    if ((ret = flv->reader.open(file)) != ERROR_SUCCESS) {
+    if ((ret = flv->writer.open(file)) != ERROR_SUCCESS) {
         srs_freep(flv);
         return NULL;
     }
     
-    if ((ret = flv->dec.initialize(&flv->reader)) != ERROR_SUCCESS) {
+    if ((ret = flv->enc.initialize(&flv->writer)) != ERROR_SUCCESS) {
         srs_freep(flv);
         return NULL;
     }
     
-    if ((ret = flv->writer.open(file)) != ERROR_SUCCESS) {
+    if ((ret = flv->reader.open(file)) != ERROR_SUCCESS) {
         srs_freep(flv);
         return NULL;
     }
     
-    if ((ret = flv->enc.initialize(&flv->writer)) != ERROR_SUCCESS) {
+    if ((ret = flv->dec.initialize(&flv->reader)) != ERROR_SUCCESS) {
         srs_freep(flv);
         return NULL;
     }

@@ -165,6 +165,7 @@ int64_t srs_get_nrecv_bytes(srs_rtmp_t rtmp);
 */
 typedef void* srs_flv_t;
 typedef int flv_bool;
+/* open flv file for both read/write. */
 srs_flv_t srs_flv_open(const char* file);
 void srs_flv_close(srs_flv_t flv);
 /* read the flv header. 9bytes header. drop the 4bytes zero previous tag size */