avformat: Fix decoder search in find stream info

Fixes Ticket3548
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/avformat.h

@@ -891,6 +891,12 @@ typedef struct AVStream {
         double (*duration_error)[2][MAX_STD_TIMEBASES];
         int64_t codec_info_duration;
         int64_t codec_info_duration_fields;
+
+        /**
+         * 0  -> decoder has not been searched for yet.
+         * >0 -> decoder found
+         * <0 -> decoder with codec_id == -found_decoder has not been found
+         */
         int found_decoder;
 
         int64_t last_duration;

libavformat/utils.c

@@ -2655,13 +2655,15 @@ static int try_decode_frame(AVFormatContext *s, AVStream *st, AVPacket *avpkt,
     if (!frame)
         return AVERROR(ENOMEM);
 
-    if (!avcodec_is_open(st->codec) && !st->info->found_decoder) {
+    if (!avcodec_is_open(st->codec) &&
+        st->info->found_decoder <= 0 &&
+        (st->codec->codec_id != -st->info->found_decoder || !st->codec->codec_id)) {
         AVDictionary *thread_opt = NULL;
 
         codec = find_decoder(s, st, st->codec->codec_id);
 
         if (!codec) {
-            st->info->found_decoder = -1;
+            st->info->found_decoder = -st->codec->codec_id;
             ret                     = -1;
             goto fail;
         }
@@ -2673,7 +2675,7 @@ static int try_decode_frame(AVFormatContext *s, AVStream *st, AVPacket *avpkt,
         if (!options)
             av_dict_free(&thread_opt);
         if (ret < 0) {
-            st->info->found_decoder = -1;
+            st->info->found_decoder = -st->codec->codec_id;
             goto fail;
         }
         st->info->found_decoder = 1;