flac_parser.c: fix case when final frame is a false positive

Should fix https://ffmpeg.org/trac/ffmpeg/ticket/2552
Only did minimal testing on a few files and fate.
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/flac_parser.c

@@ -87,6 +87,8 @@ typedef struct FLACParseContext {
     int end_padded;                /**< specifies if fifo_buf's end is padded */
     uint8_t *wrap_buf;             /**< general fifo read buffer when wrapped */
     int wrap_buf_allocated_size;   /**< actual allocated size of the buffer   */
+    FLACFrameInfo last_fi;         /**< last decoded frame header info        */
+    int last_fi_valid;             /**< set if last_fi is valid               */
 } FLACParseContext;
 
 static int frame_header_is_valid(AVCodecContext *avctx, const uint8_t *buf,
@@ -267,13 +269,12 @@ static int find_new_headers(FLACParseContext *fpc, int search_start)
     return size;
 }
 
-static int check_header_mismatch(FLACParseContext  *fpc,
-                                 FLACHeaderMarker  *header,
-                                 FLACHeaderMarker  *child,
+static int check_header_fi_mismatch(FLACParseContext  *fpc,
+                                    FLACFrameInfo     *header_fi,
+                                    FLACFrameInfo     *child_fi,
                                     int                log_level_offset)
 {
-    FLACFrameInfo  *header_fi = &header->fi, *child_fi = &child->fi;
-    int deduction = 0, deduction_expected = 0, i;
+    int deduction = 0;
     if (child_fi->samplerate != header_fi->samplerate) {
         deduction += FLAC_HEADER_CHANGED_PENALTY;
         av_log(fpc->avctx, AV_LOG_WARNING + log_level_offset,
@@ -295,6 +296,18 @@ static int check_header_mismatch(FLACParseContext  *fpc,
         av_log(fpc->avctx, AV_LOG_WARNING + log_level_offset,
                "number of channels change detected in adjacent frames\n");
     }
+    return deduction;
+}
+
+static int check_header_mismatch(FLACParseContext  *fpc,
+                                 FLACHeaderMarker  *header,
+                                 FLACHeaderMarker  *child,
+                                 int                log_level_offset)
+{
+    FLACFrameInfo  *header_fi = &header->fi, *child_fi = &child->fi;
+    int deduction, deduction_expected = 0, i;
+    deduction = check_header_fi_mismatch(fpc, header_fi, child_fi,
+                                         log_level_offset);
     /* Check sample and frame numbers. */
     if ((child_fi->frame_or_sample_num - header_fi->frame_or_sample_num
          != header_fi->blocksize) &&
@@ -399,11 +412,18 @@ static int score_header(FLACParseContext *fpc, FLACHeaderMarker *header)
     FLACHeaderMarker *child;
     int dist = 0;
     int child_score;
-
+    int base_score = FLAC_HEADER_BASE_SCORE;
     if (header->max_score != FLAC_HEADER_NOT_SCORED_YET)
         return header->max_score;
 
-    header->max_score = FLAC_HEADER_BASE_SCORE;
+    /* Modify the base score with changes from the last output header */
+    if (fpc->last_fi_valid) {
+        /* Silence the log since this will be repeated if selected */
+        base_score -= check_header_fi_mismatch(fpc, &fpc->last_fi, &header->fi,
+                                               AV_LOG_DEBUG);
+    }
+
+    header->max_score = base_score;
 
     /* Check and compute the children's scores. */
     child = header->next;
@@ -419,7 +439,7 @@ static int score_header(FLACParseContext *fpc, FLACHeaderMarker *header)
         if (FLAC_HEADER_BASE_SCORE + child_score > header->max_score) {
             /* Keep the child because the frame scoring is dynamic. */
             header->best_child = child;
-            header->max_score  = FLAC_HEADER_BASE_SCORE + child_score;
+            header->max_score  = base_score + child_score;
         }
         child = child->next;
     }
@@ -430,7 +450,7 @@ static int score_header(FLACParseContext *fpc, FLACHeaderMarker *header)
 static void score_sequences(FLACParseContext *fpc)
 {
     FLACHeaderMarker *curr;
-    int best_score = FLAC_HEADER_NOT_SCORED_YET;
+    int best_score = 0;//FLAC_HEADER_NOT_SCORED_YET;
     /* First pass to clear all old scores. */
     for (curr = fpc->headers; curr; curr = curr->next)
         curr->max_score = FLAC_HEADER_NOT_SCORED_YET;
@@ -470,6 +490,9 @@ static int get_best_header(FLACParseContext* fpc, const uint8_t **poutbuf,
                                         &fpc->wrap_buf_allocated_size);
 
     fpc->best_header_valid = 0;
+    fpc->last_fi_valid = 1;
+    fpc->last_fi = header->fi;
+
     /* Return the negative overread index so the client can compute pos.
        This should be the amount overread to the beginning of the child */
     if (child)
@@ -629,9 +652,12 @@ static int flac_parse(AVCodecParserContext *s, AVCodecContext *avctx,
     }
 
     curr = fpc->headers;
-    for (curr = fpc->headers; curr; curr = curr->next)
-        if (!fpc->best_header || curr->max_score > fpc->best_header->max_score)
+    for (curr = fpc->headers; curr; curr = curr->next) {
+        if (curr->max_score > 0 &&
+            (!fpc->best_header || curr->max_score > fpc->best_header->max_score)) {
             fpc->best_header = curr;
+        }
+    }
 
     if (fpc->best_header) {
         fpc->best_header_valid = 1;