aac_latm: Align inband PCE to the start of the payload

A strict reading of the spec seems to imply that it should be aligned to
the start of the element instance tag, but that would break all of the
samples with PCEs.

It seems like a well formed LATM stream should have its PCE in the ASC
rather than inband.

Fixes ticket 4544

libavcodec/aacdec_template.c

@@ -2949,6 +2949,7 @@ static int aac_decode_frame_int(AVCodecContext *avctx, void *data,
     int err, elem_id;
     int samples = 0, multiplier, audio_found = 0, pce_found = 0;
     int is_dmono, sce_count = 0;
+    int payload_alignment;
 
     ac->frame = data;
 
@@ -2971,6 +2972,7 @@ static int aac_decode_frame_int(AVCodecContext *avctx, void *data,
     // This may lead to an undefined profile being signaled
     ac->avctx->profile = ac->oc[1].m4ac.object_type - 1;
 
+    payload_alignment = get_bits_count(gb);
     ac->tags_mapped = 0;
     // parse
     while ((elem_type = get_bits(gb, 3)) != TYPE_END) {
@@ -3025,7 +3027,8 @@ static int aac_decode_frame_int(AVCodecContext *avctx, void *data,
             uint8_t layout_map[MAX_ELEM_ID*4][3];
             int tags;
             push_output_configuration(ac);
-            tags = decode_pce(avctx, &ac->oc[1].m4ac, layout_map, gb, 0);
+            tags = decode_pce(avctx, &ac->oc[1].m4ac, layout_map, gb,
+                              payload_alignment);
             if (tags < 0) {
                 err = tags;
                 break;