avcodec/cbs_av1: add a function to strip trailing zeroes from a buffer size

Factor it out from cbs_av1_read_metadata_itut_t35()

Reviewed-by: Mark Thompson <sw@jkqxz.net>
Signed-off-by: James Almer <jamrial@gmail.com>

libavcodec/cbs_av1.c

@@ -574,6 +574,17 @@ static int cbs_av1_get_relative_dist(const AV1RawSequenceHeader *seq,
     return diff;
 }
 
+static size_t cbs_av1_get_payload_bytes_left(GetBitContext *gbc)
+{
+    GetBitContext tmp = *gbc;
+    size_t size = 0;
+    for (int i = 0; get_bits_left(&tmp) >= 8; i++) {
+        if (get_bits(&tmp, 8))
+            size = i;
+    }
+    return size;
+}
+
 
 #define HEADER(name) do { \
         ff_cbs_trace_header(ctx, name); \

libavcodec/cbs_av1_syntax_template.c

@@ -1674,15 +1674,7 @@ static int FUNC(metadata_itut_t35)(CodedBitstreamContext *ctx, RWContext *rw,
 #ifdef READ
     // The payload runs up to the start of the trailing bits, but there might
     // be arbitrarily many trailing zeroes so we need to read through twice.
-    {
-        GetBitContext tmp = *rw;
-        current->payload_size = 0;
-        for (i = 0; get_bits_left(rw) >= 8; i++) {
-            if (get_bits(rw, 8))
-                current->payload_size = i;
-        }
-        *rw = tmp;
-    }
+    current->payload_size = cbs_av1_get_payload_bytes_left(rw);
 
     current->payload_ref = av_buffer_alloc(current->payload_size);
     if (!current->payload_ref)