aacenc: Start the lookahead pointer 1/4 of the way into the first short window.

Short windows are of length 256 and begin at sample 448.

Originally committed as revision 23871 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/aacenc.c

@@ -519,7 +519,7 @@ static int aac_encode_frame(AVCodecContext *avctx,
         chans    = tag == TYPE_CPE ? 2 : 1;
         cpe      = &s->cpe[i];
         samples2 = samples + start_ch;
-        la       = samples2 + 1024 * avctx->channels + start_ch;
+        la       = samples2 + (448+64) * avctx->channels + start_ch;
         if (!data)
             la = NULL;
         for (j = 0; j < chans; j++) {