diff --git a/libavformat/utils.c b/libavformat/utils.c
index 01b5cc512b..5b7618fe84 100644
--- a/libavformat/utils.c
+++ b/libavformat/utils.c
@@ -712,6 +712,21 @@ no_packet:
     }
 }
 
+static void force_codec_ids(AVFormatContext *s, AVStream *st)
+{
+    switch(st->codec->codec_type){
+    case AVMEDIA_TYPE_VIDEO:
+        if(s->video_codec_id)   st->codec->codec_id= s->video_codec_id;
+        break;
+    case AVMEDIA_TYPE_AUDIO:
+        if(s->audio_codec_id)   st->codec->codec_id= s->audio_codec_id;
+        break;
+    case AVMEDIA_TYPE_SUBTITLE:
+        if(s->subtitle_codec_id)st->codec->codec_id= s->subtitle_codec_id;
+        break;
+    }
+}
+
 int ff_read_packet(AVFormatContext *s, AVPacket *pkt)
 {
     int ret, i;
@@ -765,17 +780,8 @@ int ff_read_packet(AVFormatContext *s, AVPacket *pkt)
 
         st= s->streams[pkt->stream_index];
 
-        switch(st->codec->codec_type){
-        case AVMEDIA_TYPE_VIDEO:
-            if(s->video_codec_id)   st->codec->codec_id= s->video_codec_id;
-            break;
-        case AVMEDIA_TYPE_AUDIO:
-            if(s->audio_codec_id)   st->codec->codec_id= s->audio_codec_id;
-            break;
-        case AVMEDIA_TYPE_SUBTITLE:
-            if(s->subtitle_codec_id)st->codec->codec_id= s->subtitle_codec_id;
-            break;
-        }
+        force_codec_ids(s, st);
+
         /* TODO: audio: time filter; video: frame reordering (pts != dts) */
         if (s->use_wallclock_as_timestamps)
             pkt->dts = pkt->pts = av_rescale_q(av_gettime(), AV_TIME_BASE_Q, st->time_base);