avcodec/cbs_av1: don't abort when splitting Temporal Units containing OBUs with no obu_size field

The ISOBMFF and Matroska specs allow the last OBU in a Sample/Block to have
obu_has_size_field equal to 0.

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

libavcodec/cbs_av1.c

@@ -788,13 +788,6 @@ static int cbs_av1_split_fragment(CodedBitstreamContext *ctx,
         if (err < 0)
             goto fail;
 
-        if (!header.obu_has_size_field) {
-            av_log(ctx->log_ctx, AV_LOG_ERROR, "Invalid OBU for raw "
-                   "stream: size field must be present.\n");
-            err = AVERROR_INVALIDDATA;
-            goto fail;
-        }
-
         if (get_bits_left(&gbc) < 8) {
             av_log(ctx->log_ctx, AV_LOG_ERROR, "Invalid OBU: fragment "
                    "too short (%zu bytes).\n", size);
@@ -802,9 +795,12 @@ static int cbs_av1_split_fragment(CodedBitstreamContext *ctx,
             goto fail;
         }
 
-        err = cbs_av1_read_leb128(ctx, &gbc, "obu_size", &obu_size);
-        if (err < 0)
-            goto fail;
+        if (header.obu_has_size_field) {
+            err = cbs_av1_read_leb128(ctx, &gbc, "obu_size", &obu_size);
+            if (err < 0)
+                goto fail;
+        } else
+            obu_size = size - 1 - header.obu_extension_flag;
 
         pos = get_bits_count(&gbc);
         av_assert0(pos % 8 == 0 && pos / 8 <= size);