[FFmpeg-devel] [PATCH] avformat/mov: Fix get_eia608_packet c608 caption reformatting

[Pavel Koshevoy <pkoshevoy@gmail.com>]

---
 libavformat/mov.c | 40 +++++++++++++++++++++++++++++++---------
 1 file changed, 31 insertions(+), 9 deletions(-)

diff --git a/libavformat/mov.c b/libavformat/mov.c
index 85aef33b19..422e515fe8 100644
--- a/libavformat/mov.c
+++ b/libavformat/mov.c
@@ -10790,22 +10790,44 @@ static int mov_change_extradata(AVStream *st, AVPacket *pkt)
 
 static int get_eia608_packet(AVIOContext *pb, AVPacket *pkt, int size)
 {
-    int new_size, ret;
-
+    /* We can't make assumptions about the structure of the payload,
+       because it may include multiple cdat and cdt2 samples. */
+    int ret, out_size = 0;
     if (size <= 8)
         return AVERROR_INVALIDDATA;
-    new_size = ((size - 8) / 2) * 3;
-    ret = av_new_packet(pkt, new_size);
+
+    /* Allocate 3 times the required buffer size to give us enough space
+       to store the original c608 packet and (potentially 3/2 times larger)
+       reformatted data, safely. */
+    ret = av_new_packet(pkt, size * 3);
     if (ret < 0)
         return ret;
 
-    avio_skip(pb, 8);
-    for (int j = 0; j < new_size; j += 3) {
-        pkt->data[j] = 0xFC;
-        pkt->data[j+1] = avio_r8(pb);
-        pkt->data[j+2] = avio_r8(pb);
+    /* Load the original c608 payload into the last 3rd of the buffer. */
+    if (avio_read(pb, pkt->data + size * 2, size) != size)
+        return AVERROR_EOF;
+
+    /* parse and re-format the c608 payload in one pass */
+    for (uint8_t *out = pkt->data, *src = out + size * 2, *end = src + size; src + 8 <= end; ) {
+        uint32_t atom_size = AV_RB32(src);
+        uint8_t cc_field =
+            memcmp(src + 4, "cdat", 4) == 0 ? 1 :
+            memcmp(src + 4, "cdt2", 4) == 0 ? 2 :
+            0;
+
+        if (cc_field != 0) {
+            for (uint8_t *cc = src + 8, *cc_end = src + atom_size; cc < cc_end; cc += 2) {
+                out[0] = (0x1F << 3) | (1 << 2) | (cc_field - 1);
+                out[1] = cc[0];
+                out[2] = cc[1];
+                out_size += 3;
+                out += 3;
+            }
+        }
+        src += atom_size;
     }
 
+    pkt->size = out_size;
     return 0;
 }
 
-- 
2.43.0

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