[FFmpeg-devel] [PATCH v2 13/13] cbs_mpeg2.c: improve readability of start code search (part 3)

[Scott Theisen]

Separate from part 2 for a clearer diff.

Now the true loop condition has been revealed: start < buf_end

Clarify loop by moving the detection of sequence_end_codes out of the loop.
See also commit fd93d5efe64206d5f1bce8c702602353444c0c1a regarding sequence_end_codes
---
 libavcodec/cbs_mpeg2.c | 31 ++++++++++++++++++-------------
 1 file changed, 18 insertions(+), 13 deletions(-)

diff --git a/libavcodec/cbs_mpeg2.c b/libavcodec/cbs_mpeg2.c
index bf95fb7546..53aa0ed3f6 100644
--- a/libavcodec/cbs_mpeg2.c
+++ b/libavcodec/cbs_mpeg2.c
@@ -149,7 +149,7 @@ static int cbs_mpeg2_split_fragment(CodedBitstreamContext *ctx,
     CodedBitstreamUnitType unit_type;
     uint32_t start_code = -1;
     size_t unit_size;
-    int err, final = 0;
+    int err;
     int i = -1; // offset for pre-increment
 
     start = avpriv_find_start_code(start, buf_end, &start_code, 1);
@@ -161,16 +161,7 @@ static int cbs_mpeg2_split_fragment(CodedBitstreamContext *ctx,
     do {
         unit_type = start_code & 0xff;
 
-        if (start == buf_end) {
-            // The last four bytes form a start code which constitutes
-            // a unit of its own.  In this situation avpriv_find_start_code
-            // won't modify start_code at all so modify start_code so that
-            // the next unit will be treated as the last unit.
-            start_code = 0;
-        }
-        else {
-            end = avpriv_find_start_code(start, buf_end, &start_code, 1);
-        }
+        end = avpriv_find_start_code(start, buf_end, &start_code, 1);
         start--;
         // decrement so start points to the byte containing the start_code_identifier
         // (may be the last byte of fragment->data); end points to the byte
@@ -182,8 +173,8 @@ static int cbs_mpeg2_split_fragment(CodedBitstreamContext *ctx,
             unit_size = (end - 4) - start;
         } else {
            // We didn't find a start code, so this is the final unit.
+           // There is no start code to remove from end, hence not (end - 4).
            unit_size = end - start;
-           final     = 1;
         }
 
         err = ff_cbs_insert_unit_data(frag, ++i, unit_type,
@@ -193,7 +184,21 @@ static int cbs_mpeg2_split_fragment(CodedBitstreamContext *ctx,
             return err;
 
         start = end;
-    } while (!final);
+    } while (start < buf_end);
+
+    if (avpriv_start_code_is_valid(start_code)) {
+        // The last four bytes form a start code which constitutes
+        // a unit of its own, with size 1.
+
+        start--; // since start == buf_end because of the loop condition,
+        // decrement so start points to the byte containing the start_code_identifier
+        err = ff_cbs_insert_unit_data(frag, ++i, start_code & 0xFF,
+                                      (uint8_t*)start /* cast away the const to match parameter type */,
+                                      1, frag->data_ref);
+        if (err < 0) {
+            return err;
+        }
+    }
 
     return 0;
 }
-- 
2.32.0