Don't encode the first sample twice.

Originally committed as revision 9962 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/adpcm.c

@@ -537,7 +537,7 @@ static int adpcm_encode_frame(AVCodecContext *avctx,
             c->status[i].prev_sample = (signed short)samples[i];
         }
 
-        for (i=0; i<avctx->frame_size; i++) {
+        for (i=1; i<avctx->frame_size; i++) {
             put_bits(&pb, 4, adpcm_ima_compress_sample(&c->status[0], samples[avctx->channels*i]) & 0xF);
             if (avctx->channels == 2)
                 put_bits(&pb, 4, adpcm_ima_compress_sample(&c->status[1], samples[2*i+1]) & 0xF);