avcodec/dca_parser: improve frame end search
authorfoo86 <foobaz86@gmail.com>
Fri, 13 May 2016 09:48:28 +0000 (12:48 +0300)
committerJames Almer <jamrial@gmail.com>
Fri, 20 May 2016 19:36:08 +0000 (16:36 -0300)
Parse core frame size directly when searching for frame end instead of
using value extracted from previous frame.

Account for unused bits when calculating sync word distance for 14-bit
streams to avoid alias sync detection.

Parse EXSS frame size and skip over EXSS frame to avoid alias sync
detection.

Signed-off-by: James Almer <jamrial@gmail.com>
libavcodec/dca_parser.c

index bde7dfe..0b09ba5 100644 (file)
@@ -47,6 +47,14 @@ typedef struct DCAParseContext {
 #define CORE_MARKER(state)      ((state >> 16) & 0xFFFFFFFF)
 #define EXSS_MARKER(state)      (state & 0xFFFFFFFF)
 
+#define STATE_LE(state)     (((state & 0xFF00FF00) >> 8) | ((state & 0x00FF00FF) << 8))
+#define STATE_14(state)     (((state & 0x3FFF0000) >> 8) | ((state & 0x00003FFF) >> 6))
+
+#define CORE_FRAMESIZE(state)   (((state >> 4) & 0x3FFF) + 1)
+#define EXSS_FRAMESIZE(state)   ((state & 0x2000000000) ? \
+                                 ((state >>  5) & 0xFFFFF) + 1 : \
+                                 ((state >> 13) & 0x0FFFF) + 1)
+
 /**
  * Find the end of the current frame in the bitstream.
  * @return the position of the first byte of the next frame, or -1
@@ -54,12 +62,13 @@ typedef struct DCAParseContext {
 static int dca_find_frame_end(DCAParseContext *pc1, const uint8_t *buf,
                               int buf_size)
 {
-    int start_found, i;
+    int start_found, size, i;
     uint64_t state;
     ParseContext *pc = &pc1->pc;
 
     start_found = pc->frame_start_found;
     state       = pc->state64;
+    size        = pc1->size;
 
     i = 0;
     if (!start_found) {
@@ -80,15 +89,75 @@ static int dca_find_frame_end(DCAParseContext *pc1, const uint8_t *buf,
             }
         }
     }
+
     if (start_found) {
         for (; i < buf_size; i++) {
-            pc1->size++;
+            size++;
             state = (state << 8) | buf[i];
+
+            if (start_found == 1) {
+                switch (pc1->lastmarker) {
+                case DCA_SYNCWORD_CORE_BE:
+                    if (size == 2) {
+                        pc1->framesize = CORE_FRAMESIZE(state);
+                        start_found    = 2;
+                    }
+                    break;
+                case DCA_SYNCWORD_CORE_LE:
+                    if (size == 2) {
+                        pc1->framesize = CORE_FRAMESIZE(STATE_LE(state));
+                        start_found    = 2;
+                    }
+                    break;
+                case DCA_SYNCWORD_CORE_14B_BE:
+                    if (size == 4) {
+                        pc1->framesize = CORE_FRAMESIZE(STATE_14(state)) * 8 / 14 * 2;
+                        start_found    = 2;
+                    }
+                    break;
+                case DCA_SYNCWORD_CORE_14B_LE:
+                    if (size == 4) {
+                        pc1->framesize = CORE_FRAMESIZE(STATE_14(STATE_LE(state))) * 8 / 14 * 2;
+                        start_found    = 2;
+                    }
+                    break;
+                case DCA_SYNCWORD_SUBSTREAM:
+                    if (size == 6) {
+                        pc1->framesize = EXSS_FRAMESIZE(state);
+                        start_found    = 2;
+                    }
+                    break;
+                default:
+                    av_assert0(0);
+                }
+                continue;
+            }
+
+            if (pc1->lastmarker == DCA_SYNCWORD_CORE_BE) {
+                if (pc1->framesize > size + 2)
+                    continue;
+
+                if (start_found == 2 && IS_EXSS_MARKER(state)) {
+                    pc1->framesize = size + 2;
+                    start_found    = 3;
+                    continue;
+                }
+
+                if (start_found == 3) {
+                    if (size == pc1->framesize + 4) {
+                        pc1->framesize += EXSS_FRAMESIZE(state);
+                        start_found     = 4;
+                    }
+                    continue;
+                }
+            }
+
+            if (pc1->framesize > size)
+                continue;
+
             if (IS_MARKER(state) &&
                 (pc1->lastmarker == CORE_MARKER(state) ||
                  pc1->lastmarker == DCA_SYNCWORD_SUBSTREAM)) {
-                if (pc1->framesize > pc1->size)
-                    continue;
                 pc->frame_start_found = 0;
                 pc->state64           = -1;
                 pc1->size             = 0;
@@ -96,8 +165,10 @@ static int dca_find_frame_end(DCAParseContext *pc1, const uint8_t *buf,
             }
         }
     }
+
     pc->frame_start_found = start_found;
     pc->state64           = state;
+    pc1->size             = size;
     return END_NOT_FOUND;
 }
 
@@ -110,11 +181,11 @@ static av_cold int dca_parse_init(AVCodecParserContext *s)
 }
 
 static int dca_parse_params(const uint8_t *buf, int buf_size, int *duration,
-                            int *sample_rate, int *framesize)
+                            int *sample_rate)
 {
     GetBitContext gb;
     uint8_t hdr[12 + AV_INPUT_BUFFER_PADDING_SIZE] = { 0 };
-    int ret, sample_blocks, sr_code;
+    int ret, sample_blocks;
 
     if (buf_size < 12)
         return AVERROR_INVALIDDATA;
@@ -130,13 +201,8 @@ static int dca_parse_params(const uint8_t *buf, int buf_size, int *duration,
         return AVERROR_INVALIDDATA;
     *duration = 256 * (sample_blocks / 8);
 
-    *framesize = get_bits(&gb, 14) + 1;
-    if (*framesize < 95)
-        return AVERROR_INVALIDDATA;
-
-    skip_bits(&gb, 6);
-    sr_code      = get_bits(&gb, 4);
-    *sample_rate = avpriv_dca_sample_rates[sr_code];
+    skip_bits(&gb, 20);
+    *sample_rate = avpriv_dca_sample_rates[get_bits(&gb, 4)];
     if (*sample_rate == 0)
         return AVERROR_INVALIDDATA;
 
@@ -164,7 +230,7 @@ static int dca_parse(AVCodecParserContext *s, AVCodecContext *avctx,
     }
 
     /* read the duration and sample rate from the frame header */
-    if (!dca_parse_params(buf, buf_size, &duration, &sample_rate, &pc1->framesize)) {
+    if (!dca_parse_params(buf, buf_size, &duration, &sample_rate)) {
         if (!avctx->sample_rate)
             avctx->sample_rate = sample_rate;
         s->duration = av_rescale(duration, avctx->sample_rate, sample_rate);