diff --git a/libavformat/smoothstreamingenc.c b/libavformat/smoothstreamingenc.c
index 08e6526533..339a9bb08d 100644
--- a/libavformat/smoothstreamingenc.c
+++ b/libavformat/smoothstreamingenc.c
@@ -239,6 +239,7 @@ static int ism_write_header(AVFormatContext *s)
             goto fail;
         }
         avcodec_copy_context(st->codec, s->streams[i]->codec);
+        st->sample_aspect_ratio = s->streams[i]->sample_aspect_ratio;
 
         ctx->pb = avio_alloc_context(os->iobuf, sizeof(os->iobuf), AVIO_FLAG_WRITE, os, NULL, ism_write, ism_seek);
         if (!ctx->pb) {