diff --git a/libavcodec/mpegaudiodec.c b/libavcodec/mpegaudiodec.c
index 1691a77e4d805ad74f828c958197bc2072982538..df2803397c8d28f509a496c4a6eb7dccd0a63cd2 100644
--- a/libavcodec/mpegaudiodec.c
+++ b/libavcodec/mpegaudiodec.c
@@ -2596,11 +2596,10 @@ static int decode_frame_mp3on4(AVCodecContext * avctx,
         }
 
         ff_mpegaudio_decode_header(m, header);
-        mp_decode_frame(m, decoded_buf, start, fsize);
+        out_size += mp_decode_frame(m, decoded_buf, start, fsize);
 
-        n = MPA_FRAME_SIZE * m->nb_channels;
-        out_size += n * sizeof(OUT_INT);
         if(s->frames > 1) {
+            n = m->avctx->frame_size*m->nb_channels;
             /* interleave output data */
             bp = out_samples + coff[fr];
             if(m->nb_channels == 1) {