diff --git a/audio/decode/ad_spdif.c b/audio/decode/ad_spdif.c
index f7891767d2..3da5def868 100644
--- a/audio/decode/ad_spdif.c
+++ b/audio/decode/ad_spdif.c
@@ -117,13 +117,11 @@ static int init(struct dec_audio *da, const char *decoder)
     int samplerate = 0;
     switch (stream->codec->codec_id) {
     case AV_CODEC_ID_AAC:
-        spdif_ctx->iec61937_packet_size = 16384;
         sample_format                   = AF_FORMAT_S_AAC;
         samplerate                      = 48000;
         num_channels                    = 2;
         break;
     case AV_CODEC_ID_AC3:
-        spdif_ctx->iec61937_packet_size = 6144;
         sample_format                   = AF_FORMAT_S_AC3;
         samplerate                      = 48000;
         num_channels                    = 2;
@@ -131,31 +129,26 @@ static int init(struct dec_audio *da, const char *decoder)
     case AV_CODEC_ID_DTS:
         if (da->opts->dtshd) {
             av_dict_set(&format_opts, "dtshd_rate", "768000", 0); // 4*192000
-            spdif_ctx->iec61937_packet_size = 32768;
             sample_format                   = AF_FORMAT_S_DTSHD;
             samplerate                      = 192000;
             num_channels                    = 2*4;
         } else {
-            spdif_ctx->iec61937_packet_size = 32768;
             sample_format                   = AF_FORMAT_S_DTS;
             samplerate                      = 48000;
             num_channels                    = 2;
         }
         break;
     case AV_CODEC_ID_EAC3:
-        spdif_ctx->iec61937_packet_size = 24576;
         sample_format                   = AF_FORMAT_S_EAC3;
         samplerate                      = 192000;
         num_channels                    = 2;
         break;
     case AV_CODEC_ID_MP3:
-        spdif_ctx->iec61937_packet_size = 4608;
         sample_format                   = AF_FORMAT_S_MP3;
         samplerate                      = 48000;
         num_channels                    = 2;
         break;
     case AV_CODEC_ID_TRUEHD:
-        spdif_ctx->iec61937_packet_size = 61440;
         sample_format                   = AF_FORMAT_S_TRUEHD;
         samplerate                      = 192000;
         num_channels                    = 8;
@@ -166,6 +159,7 @@ static int init(struct dec_audio *da, const char *decoder)
     mp_audio_set_num_channels(&spdif_ctx->fmt, num_channels);
     mp_audio_set_format(&spdif_ctx->fmt, sample_format);
     spdif_ctx->fmt.rate = samplerate;
+    spdif_ctx->iec61937_packet_size = af_format_sample_alignment(sample_format);
 
     if (avformat_write_header(lavf_ctx, &format_opts) < 0) {
         MP_FATAL(da, "libavformat spdif initialization failed.\n");
diff --git a/audio/format.c b/audio/format.c
index 08b369c090..5e83ead1b2 100644
--- a/audio/format.c
+++ b/audio/format.c
@@ -227,3 +227,16 @@ int af_format_conversion_score(int dst_format, int src_format)
         score -= 2048;  // has to convert float<->int
     return score;
 }
+
+int af_format_sample_alignment(int format)
+{
+    switch (format) {
+    case AF_FORMAT_S_AAC:       return 16384;
+    case AF_FORMAT_S_AC3:       return 6144;
+    case AF_FORMAT_S_DTSHD:     return 32768;
+    case AF_FORMAT_S_EAC3:      return 24576;
+    case AF_FORMAT_S_MP3:       return 4608;
+    case AF_FORMAT_S_TRUEHD:    return 61440;
+    default:                    return 1;
+    }
+}
diff --git a/audio/format.h b/audio/format.h
index b3ac0000c8..910b952fd2 100644
--- a/audio/format.h
+++ b/audio/format.h
@@ -125,4 +125,6 @@ void af_fill_silence(void *dst, size_t bytes, int format);
 
 int af_format_conversion_score(int dst_format, int src_format);
 
+int af_format_sample_alignment(int format);
+
 #endif /* MPLAYER_AF_FORMAT_H */