set bps to uncompressed original sound data for compressed audio

according to aiff specs, qt set it to 16 for mace and ima4,
fail if block align is not set.

Originally committed as revision 12198 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/aiff.c

@@ -189,7 +189,12 @@ static int aiff_write_header(AVFormatContext *s)
     put_be32(pb, 0);                    /* file length */
     put_tag(pb, aifc ? "AIFC" : "AIFF");
 
-    if (aifc) {
+    if (aifc) { // compressed audio
+        enc->bits_per_sample = 16;
+        if (!enc->block_align) {
+            av_log(s, AV_LOG_ERROR, "block align not set\n");
+            return -1;
+        }
         /* Version chunk */
         put_tag(pb, "FVER");
         put_be32(pb, 4);