lavf: Cleanup try_decode_frame() logic.

This fixes AAC playback in ffplay.

libavcodec/aacdec.c

@@ -568,9 +568,6 @@ static av_cold int aac_decode_init(AVCodecContext *avctx)
     ac->m4ac.sample_rate = avctx->sample_rate;
 
     if (avctx->extradata_size > 0) {
-        avctx->channels    = 0;
-        avctx->frame_size  = 0;
-        avctx->sample_rate = 0;
         if (decode_audio_specific_config(ac, ac->avctx, &ac->m4ac,
                                          avctx->extradata,
                                          avctx->extradata_size) < 0)

libavformat/utils.c

@@ -2090,7 +2090,8 @@ static int try_decode_frame(AVStream *st, AVPacket *avpkt, AVDictionary **option
             return ret;
     }
 
-    if(!has_codec_parameters(st->codec) || !has_decode_delay_been_guessed(st)){
+    if(!has_codec_parameters(st->codec) || !has_decode_delay_been_guessed(st) ||
+       (!st->codec_info_nb_frames && st->codec->codec->capabilities & CODEC_CAP_CHANNEL_CONF)) {
         switch(st->codec->codec_type) {
         case AVMEDIA_TYPE_VIDEO:
             avcodec_get_frame_defaults(&picture);
@@ -2387,10 +2388,6 @@ int avformat_find_stream_info(AVFormatContext *ic, AVDictionary **options)
            least one frame of codec data, this makes sure the codec initializes
            the channel configuration and does not only trust the values from the container.
         */
-        if (!has_codec_parameters(st->codec) ||
-            !has_decode_delay_been_guessed(st) ||
-            (st->codec->codec &&
-             st->codec->codec->capabilities & CODEC_CAP_CHANNEL_CONF))
         try_decode_frame(st, pkt, (options && i <= orig_nb_streams )? &options[i] : NULL);
 
         st->codec_info_nb_frames++;