diff --git a/lib/src/includes/signed_video_sign.h b/lib/src/includes/signed_video_sign.h
index ba4f65f..f6e11a2 100644
--- a/lib/src/includes/signed_video_sign.h
+++ b/lib/src/includes/signed_video_sign.h
@@ -502,10 +502,13 @@ signed_video_set_recurrence_interval_frames(signed_video_t *self, unsigned recur
  * If this API is not used, SEI payload is written with EPBs, hence equivalent with setting
  * |sei_epb| to True.
  *
+ * NOTE: AV1 does not have emulation prevention. Therefore, this API is not supported for AV1.
+ *
  * @param self Session struct pointer
  * @param sei_epb SEI payload written with EPB (default True)
  *
  * @returns SV_OK SEI w/o EPB was successfully set,
+ *          SV_NOT_SUPPORTED if codec is AV1,
  *          SV_INVALID_PARAMETER Invalid parameter.
  */
 SignedVideoReturnCode
diff --git a/lib/src/legacy/legacy_h26x_common.c b/lib/src/legacy/legacy_h26x_common.c
index c90beb3..9b57875 100644
--- a/lib/src/legacy/legacy_h26x_common.c
+++ b/lib/src/legacy/legacy_h26x_common.c
@@ -156,7 +156,7 @@ legacy_gop_info_reset(legacy_gop_info_t *gop_info)
   gop_info->verified_signature_hash = -1;
   // If a reset is forced, the stored hashes in |hash_list| have no meaning anymore.
   gop_info->list_idx = 0;
-  gop_info->has_reference_hash = false;
+  gop_info->has_reference_hash = true;
   gop_info->global_gop_counter_is_synced = false;
 }
 
diff --git a/lib/src/signed_video_h26x_common.c b/lib/src/signed_video_h26x_common.c
index 840ba7b..b9fa320 100644
--- a/lib/src/signed_video_h26x_common.c
+++ b/lib/src/signed_video_h26x_common.c
@@ -37,7 +37,7 @@
 #include "includes/signed_video_signing_plugin.h"
 #include "signed_video_authenticity.h"  // latest_validation_init()
 #include "signed_video_defines.h"  // svrc_t
-#include "signed_video_h26x_internal.h"  // h26x_nalu_list_item_t
+#include "signed_video_h26x_internal.h"  // h26x_nalu_list_item_t, METADATA_TYPE_USER_PRIVATE
 #include "signed_video_h26x_nalu_list.h"  // h26x_nalu_list_create()
 #include "signed_video_internal.h"  // gop_info_t, gop_state_t, MAX_HASH_SIZE, DEFAULT_HASH_SIZE
 #include "signed_video_openssl_internal.h"
@@ -46,7 +46,6 @@
 #define USER_DATA_UNREGISTERED 5
 #define H264_NALU_HEADER_LEN 1  // length of forbidden_zero_bit, nal_ref_idc and nal_unit_type
 #define H265_NALU_HEADER_LEN 2  // length of nal_unit_header as per ISO/ITU spec
-#define METADATA_TYPE_USER_PRIVATE 25
 #define AV1_OBU_HEADER_LEN 1
 // The salt added to the recursive hash to get the final gop_hash
 #define GOP_HASH_SALT 1
@@ -259,7 +258,7 @@ gop_info_reset(gop_info_t *gop_info)
   gop_info->verified_signature_hash = -1;
   // If a reset is forced, the stored hashes in |hash_list| have no meaning anymore.
   gop_info->list_idx = 0;
-  gop_info->has_reference_hash = false;
+  gop_info->has_reference_hash = true;
   gop_info->global_gop_counter_is_synced = false;
 }
 
@@ -1149,11 +1148,11 @@ hash_and_add(signed_video_t *self, const h26x_nalu_t *nalu)
   svrc_t status = SV_UNKNOWN_FAILURE;
   SV_TRY()
     if (nalu->is_first_nalu_part && !nalu->is_last_nalu_part) {
-      // If this is the first part of a non-complete NALU, initialize the |crypto_handle| to enable
-      // sequentially updating the hash with more parts.
+      // If this is the first part of a non-complete NALU/OBU, initialize the |crypto_handle| to
+      // enable sequentially updating the hash with more parts.
       SV_THROW(openssl_init_hash(self->crypto_handle, false));
     }
-    // Select hash function, hash the NALU and store as 'latest hash'
+    // Select hash function, hash the NALU/OBU and store as 'latest hash'
     hash_wrapper_t hash_wrapper = get_hash_wrapper(self, nalu);
     SV_THROW(hash_wrapper(self, nalu, nalu_hash, hash_size));
 #ifdef SIGNED_VIDEO_DEBUG
@@ -1274,7 +1273,7 @@ signed_video_create(SignedVideoCodec codec)
     self->authenticity_level = DEFAULT_AUTHENTICITY_LEVEL;
     self->recurrence = RECURRENCE_ALWAYS;
     self->add_public_key_to_sei = true;
-    self->sei_epb = true;
+    self->sei_epb = codec != SV_CODEC_AV1;
     self->signing_started = false;
     self->sign_data = sign_or_verify_data_create();
     self->sign_data->hash_size = openssl_get_hash_size(self->crypto_handle);
diff --git a/lib/src/signed_video_h26x_internal.h b/lib/src/signed_video_h26x_internal.h
index 823d5d3..51e92ba 100644
--- a/lib/src/signed_video_h26x_internal.h
+++ b/lib/src/signed_video_h26x_internal.h
@@ -26,6 +26,8 @@
 #include "signed_video_defines.h"  // svrc_t
 #include "signed_video_internal.h"  // gop_info_t, gop_state_t, MAX_HASH_SIZE
 
+#define METADATA_TYPE_USER_PRIVATE 25
+
 typedef struct _h26x_nalu_list_item_t h26x_nalu_list_item_t;
 
 typedef enum {
diff --git a/lib/src/signed_video_h26x_sign.c b/lib/src/signed_video_h26x_sign.c
index 96297f8..65a7c0d 100644
--- a/lib/src/signed_video_h26x_sign.c
+++ b/lib/src/signed_video_h26x_sign.c
@@ -28,7 +28,7 @@
 #include "includes/signed_video_signing_plugin.h"
 #include "signed_video_authenticity.h"  // allocate_memory_and_copy_string
 #include "signed_video_defines.h"  // svrc_t, sv_tlv_tag_t
-#include "signed_video_h26x_internal.h"  // parse_nalu_info()
+#include "signed_video_h26x_internal.h"  // parse_nalu_info(), METADATA_TYPE_USER_PRIVATE
 #include "signed_video_internal.h"  // gop_info_t
 #include "signed_video_openssl_internal.h"
 #include "signed_video_tlv.h"  // tlv_list_encode_or_get_size()
@@ -248,9 +248,29 @@ generate_sei_nalu(signed_video_t *self, uint8_t **payload, uint8_t **payload_sig
     sei_buffer_size += payload_size / 256 + 1;  // Size field
     sei_buffer_size += payload_size;
     sei_buffer_size += 1;  // Stop bit in a separate byte
+    if (self->codec != SV_CODEC_AV1) {
+      sei_buffer_size += self->codec == SV_CODEC_H264 ? 6 : 7;  // NALU header
+      sei_buffer_size += payload_size / 256 + 1;  // Size field
+      sei_buffer_size += payload_size;
+      sei_buffer_size += 1;  // Stop bit in a separate byte
+    } else {
+      payload_size += 3;  // 2 trailing-bit bytes, 1 metadata_type byte
+      int payload_size_bytes = 0;
+      size_t tmp_payload_size = payload_size;
+      while (tmp_payload_size > 0) {
+        payload_size_bytes++;
+        tmp_payload_size >>= 7;
+      }
+      sei_buffer_size += 1;  // OBU header
+      sei_buffer_size += payload_size_bytes;  // Size field
+      sei_buffer_size += payload_size;
+    }
 
-    // Secure enough memory for emulation prevention. Worst case will add 1 extra byte per 3 bytes.
-    sei_buffer_size = sei_buffer_size * 4 / 3;
+    if (self->codec != SV_CODEC_AV1) {
+      // Secure enough memory for emulation prevention. Worst case will add 1 extra byte per 3
+      // bytes.
+      sei_buffer_size = sei_buffer_size * 4 / 3;
+    }
 
     // Allocate memory for payload + SEI header to return
     *payload = (uint8_t *)malloc(sei_buffer_size);
@@ -263,30 +283,54 @@ generate_sei_nalu(signed_video_t *self, uint8_t **payload, uint8_t **payload_sig
     // Reset last_two_bytes before writing bytes
     self->last_two_bytes = LAST_TWO_BYTES_INIT_VALUE;
     uint16_t *last_two_bytes = &self->last_two_bytes;
-    // Start code prefix
-    *payload_ptr++ = 0x00;
-    *payload_ptr++ = 0x00;
-    *payload_ptr++ = 0x00;
-    *payload_ptr++ = 0x01;
-
-    if (self->codec == SV_CODEC_H264) {
-      write_byte(last_two_bytes, &payload_ptr, 0x06, false);  // SEI NAL type
-    } else if (self->codec == SV_CODEC_H265) {
-      write_byte(last_two_bytes, &payload_ptr, 0x4E, false);  // SEI NAL type
-      // nuh_layer_id and nuh_temporal_id_plus1
-      write_byte(last_two_bytes, &payload_ptr, 0x01, false);
-    }
-    // last_payload_type_byte : user_data_unregistered
-    write_byte(last_two_bytes, &payload_ptr, 0x05, false);
-
-    // Payload size
-    size_t size_left = payload_size;
-    while (size_left >= 0xFF) {
-      write_byte(last_two_bytes, &payload_ptr, 0xFF, false);
-      size_left -= 0xFF;
+    if (self->codec != SV_CODEC_AV1) {
+      // Start code prefix
+      *payload_ptr++ = 0x00;
+      *payload_ptr++ = 0x00;
+      *payload_ptr++ = 0x00;
+      *payload_ptr++ = 0x01;
+
+      if (self->codec == SV_CODEC_H264) {
+        write_byte(last_two_bytes, &payload_ptr, 0x06, false);  // SEI NAL type
+      } else if (self->codec == SV_CODEC_H265) {
+        write_byte(last_two_bytes, &payload_ptr, 0x4E, false);  // SEI NAL type
+        // nuh_layer_id and nuh_temporal_id_plus1
+        write_byte(last_two_bytes, &payload_ptr, 0x01, false);
+      }
+      // last_payload_type_byte : user_data_unregistered
+      write_byte(last_two_bytes, &payload_ptr, 0x05, false);
+
+      // Payload size
+      size_t size_left = payload_size;
+      while (size_left >= 0xFF) {
+        write_byte(last_two_bytes, &payload_ptr, 0xFF, false);
+        size_left -= 0xFF;
+      }
+      // last_payload_size_byte - u(8)
+      write_byte(last_two_bytes, &payload_ptr, (uint8_t)size_left, false);
+    } else {
+      write_byte(last_two_bytes, &payload_ptr, 0x2A, false);  // OBU header
+      // Write payload size
+      size_t size_left = payload_size;
+      while (size_left > 0) {
+        // get first 7 bits
+        int byte = (0x7F & size_left);
+        // Check if more bytes to come
+        size_left >>= 7;
+        if (size_left > 0) {
+          // More bytes to come. Set highest bit
+          byte |= 0x80;
+        } else {
+          // No more bytes to come. Clear highest bit
+          byte &= 0x7F;
+        }
+        write_byte(last_two_bytes, &payload_ptr, byte, false);  // obu_size
+      }
+      // Write metadata_type
+      write_byte(last_two_bytes, &payload_ptr, METADATA_TYPE_USER_PRIVATE, false);  // metadata_type
+      // Intermediate trailing byte
+      write_byte(last_two_bytes, &payload_ptr, 0x80, false);  // trailing byte
     }
-    // last_payload_size_byte - u(8)
-    write_byte(last_two_bytes, &payload_ptr, (uint8_t)size_left, false);
 
     // User data unregistered UUID field
     h26x_set_nal_uuid_type(self, &payload_ptr, UUID_TYPE_SIGNED_VIDEO);
@@ -402,7 +446,7 @@ get_sign_and_complete_sei_nalu(signed_video_t *self,
       tlv_list_encode_or_get_size(self, gop_info_encoders, num_gop_encoders, payload_ptr);
   payload_ptr += written_size;
 
-  // Stop bit
+  // Stop bit (Trailing bit identical for both H.26x and AV1)
   write_byte(last_two_bytes, &payload_ptr, 0x80, false);
 
 #ifdef SIGNED_VIDEO_DEBUG
@@ -502,11 +546,6 @@ signed_video_add_nalu_part_for_signing_with_timestamp(signed_video_t *self,
     }
     nalu.hashable_data_size = nalu_data_size;
   }
-  if (self->codec == SV_CODEC_AV1) {
-    // Not yet implemented, but return SV_OK to run through tests.
-    free(nalu.nalu_data_wo_epb);
-    return prepare_for_nalus_to_prepend(self);
-  }
 
   svrc_t status = SV_UNKNOWN_FAILURE;
   SV_TRY()
@@ -884,6 +923,7 @@ SignedVideoReturnCode
 signed_video_set_sei_epb(signed_video_t *self, bool sei_epb)
 {
   if (!self) return SV_INVALID_PARAMETER;
+  if (self->codec == SV_CODEC_AV1) return SV_NOT_SUPPORTED;
   self->sei_epb = sei_epb;
   return SV_OK;
 }
diff --git a/tests/check/check_signed_video_sign.c b/tests/check/check_signed_video_sign.c
index f69358f..1149bd7 100644
--- a/tests/check/check_signed_video_sign.c
+++ b/tests/check/check_signed_video_sign.c
@@ -38,6 +38,10 @@
 #include "test_helpers.h"
 #include "test_stream.h"
 
+/* General comments to the validation tests.
+ * All tests loop through the settings in settings[NUM_SETTINGS]; See signed_video_helpers.h. The
+ * index in the loop is _i and something the check test framework provides. */
+
 static void
 setup()
 {
@@ -167,8 +171,6 @@ get_seis(signed_video_t *sv, int num_seis_to_get, int *num_seis_gotten)
  */
 START_TEST(api_inputs)
 {
-  // This test runs in a loop with loop index _i, corresponding to struct sv_setting _i in
-  // |settings|; See signed_video_helpers.h.
   SignedVideoReturnCode sv_rc;
   SignedVideoCodec codec = settings[_i].codec;
   sign_algo_t algo = SIGN_ALGO_ECDSA;
@@ -236,10 +238,15 @@ START_TEST(api_inputs)
   // Setting emulation prevention.
   sv_rc = signed_video_set_sei_epb(NULL, false);
   ck_assert_int_eq(sv_rc, SV_INVALID_PARAMETER);
-  sv_rc = signed_video_set_sei_epb(sv, false);
-  ck_assert_int_eq(sv_rc, SV_OK);
-  sv_rc = signed_video_set_sei_epb(sv, true);
-  ck_assert_int_eq(sv_rc, SV_OK);
+  if (codec != SV_CODEC_AV1) {
+    sv_rc = signed_video_set_sei_epb(sv, false);
+    ck_assert_int_eq(sv_rc, SV_OK);
+    sv_rc = signed_video_set_sei_epb(sv, true);
+    ck_assert_int_eq(sv_rc, SV_OK);
+  } else {
+    ck_assert_int_eq(signed_video_set_sei_epb(sv, false), SV_NOT_SUPPORTED);
+    ck_assert_int_eq(signed_video_set_sei_epb(sv, true), SV_NOT_SUPPORTED);
+  }
 
   // Checking signed_video_set_hash_algo().
   sv_rc = signed_video_set_hash_algo(NULL, "sha512");
@@ -359,9 +366,6 @@ END_TEST
  */
 START_TEST(incorrect_operation)
 {
-  // This test runs in a loop with loop index _i, corresponding to struct sv_setting _i in
-  // |settings|; See signed_video_helpers.h.
-
   SignedVideoCodec codec = settings[_i].codec;
 
   signed_video_t *sv = signed_video_create(codec);
@@ -420,10 +424,6 @@ END_TEST
  * pointer inputs. */
 START_TEST(vendor_axis_communications_operation)
 {
-  // This test runs in a loop with loop index _i, corresponding to struct sv_setting _i in
-  // |settings|; See signed_video_helpers.h.
-  if (settings[_i].codec == SV_CODEC_AV1) return;
-
   SignedVideoReturnCode sv_rc;
   struct sv_setting setting = settings[_i];
   signed_video_t *sv = get_initialized_signed_video(setting, false);
@@ -503,12 +503,8 @@ START_TEST(correct_nalu_sequence_without_eos)
   // |settings|; See signed_video_helpers.h.
 
   test_stream_t *list = create_signed_nalus("IPPIPPIPPIPPIPPIPP", settings[_i]);
-  if (settings[_i].codec == SV_CODEC_AV1) {
-    test_stream_check_types(list, "IPPIPPIPPIPPIPPIPP");
-  } else {
-    test_stream_check_types(list, "IPPISPPISPPISPPISPPISPP");
-    verify_seis(list, settings[_i]);
-  }
+  test_stream_check_types(list, "IPPISPPISPPISPPISPPISPP");
+  verify_seis(list, settings[_i]);
   test_stream_free(list);
 }
 END_TEST
@@ -544,8 +540,7 @@ END_TEST
 
 START_TEST(correct_multislice_nalu_sequence_without_eos)
 {
-  // This test runs in a loop with loop index _i, corresponding to struct sv_setting _i in
-  // |settings|; See signed_video_helpers.h.
+  // For AV1, multi-slices are covered in one single OBU (OBU Frame).
   if (settings[_i].codec == SV_CODEC_AV1) return;
 
   test_stream_t *list = create_signed_nalus("IiPpPpIiPpPp", settings[_i]);
@@ -569,10 +564,6 @@ END_TEST
  */
 START_TEST(sei_increase_with_gop_length)
 {
-  // This test runs in a loop with loop index _i, corresponding to struct sv_setting _i in
-  // |settings|; See signed_video_helpers.h.
-  if (settings[_i].codec == SV_CODEC_AV1) return;
-
   struct sv_setting setting = settings[_i];
   // Turn off emulation prevention
   setting.ep_before_signing = false;
@@ -600,10 +591,6 @@ END_TEST
  */
 START_TEST(fallback_to_gop_level)
 {
-  // This test runs in a loop with loop index _i, corresponding to struct sv_setting _i in
-  // |settings|; See signed_video_helpers.h.
-  if (settings[_i].codec == SV_CODEC_AV1) return;
-
   // By construction, run the test for SV_AUTHENTICITY_LEVEL_FRAME only.
   if (settings[_i].auth_level != SV_AUTHENTICITY_LEVEL_FRAME) return;
 
@@ -641,10 +628,6 @@ END_TEST
  */
 START_TEST(undefined_nalu_in_sequence)
 {
-  // This test runs in a loop with loop index _i, corresponding to struct sv_setting _i in
-  // |settings|; See signed_video_helpers.h.
-  if (settings[_i].codec == SV_CODEC_AV1) return;
-
   test_stream_t *list = create_signed_nalus("IPXPIPPIP", settings[_i]);
   test_stream_check_types(list, "IPXPISPPISP");
   verify_seis(list, settings[_i]);
@@ -662,7 +645,6 @@ END_TEST
  */
 START_TEST(two_completed_seis_pending)
 {
-  if (settings[_i].codec == SV_CODEC_AV1) return;
 #ifdef SIGNED_VIDEO_DEBUG
   // Verification the signature is not yet working for buffered signatures.
   return;
@@ -751,8 +733,6 @@ END_TEST
  */
 START_TEST(golden_sei_created)
 {
-  if (settings[_i].codec == SV_CODEC_AV1) return;
-
   SignedVideoReturnCode sv_rc;
   signed_video_t *sv = get_initialized_signed_video(settings[_i], false);
   ck_assert(sv);
@@ -789,7 +769,6 @@ END_TEST
  */
 START_TEST(two_completed_seis_pending_legacy)
 {
-  if (settings[_i].codec == SV_CODEC_AV1) return;
 #ifdef SIGNED_VIDEO_DEBUG
   // Verification the signature is not yet working for buffered signatures.
   return;
@@ -856,10 +835,6 @@ END_TEST
  */
 START_TEST(correct_timestamp)
 {
-  // This test runs in a loop with loop index _i, corresponding to struct sv_setting _i in
-  // |settings|; See signed_video_helpers.h.
-  if (settings[_i].codec == SV_CODEC_AV1) return;
-
   SignedVideoCodec codec = settings[_i].codec;
   SignedVideoReturnCode sv_rc;
 
@@ -942,10 +917,6 @@ END_TEST
  */
 START_TEST(correct_signing_nalus_in_parts)
 {
-  // This test runs in a loop with loop index _i, corresponding to struct sv_setting _i in
-  // |settings|; See signed_video_helpers.h.
-  if (settings[_i].codec == SV_CODEC_AV1) return;
-
   test_stream_t *list = create_signed_splitted_nalus("IPPIPP", settings[_i]);
   test_stream_check_types(list, "IPPISPP");
   verify_seis(list, settings[_i]);
@@ -959,8 +930,7 @@ END_TEST
 #define NUM_EPB_CASES 2
 START_TEST(w_wo_emulation_prevention_bytes)
 {
-  // This test runs in a loop with loop index _i, corresponding to struct sv_setting _i in
-  // |settings|; See signed_video_helpers.h.
+  // Emulation prevention does not apply to AV1.
   if (settings[_i].codec == SV_CODEC_AV1) return;
 
   struct sv_setting setting = settings[_i];
@@ -1034,10 +1004,6 @@ END_TEST
  * Verify the setter for maximum SEI payload size. */
 START_TEST(limited_sei_payload_size)
 {
-  // This test runs in a loop with loop index _i, corresponding to struct sv_setting _i in
-  // |settings|; See signed_video_helpers.h.
-  if (settings[_i].codec == SV_CODEC_AV1) return;
-
   // No need to run this with GOP level authentication, since only frame level
   // authentication can dynamically affect the payload size.
   if (settings[_i].auth_level != SV_AUTHENTICITY_LEVEL_FRAME) return;
diff --git a/tests/check/test_helpers.c b/tests/check/test_helpers.c
index 894df27..2bc8855 100644
--- a/tests/check/test_helpers.c
+++ b/tests/check/test_helpers.c
@@ -96,8 +96,8 @@ struct sv_setting settings[NUM_SETTINGS] = {
     {SV_CODEC_H264, SV_AUTHENTICITY_LEVEL_FRAME, true, true, false, 0, "sha512", 0, 1, false,
         false},
     // AV1 tests
-    {SV_CODEC_AV1, SV_AUTHENTICITY_LEVEL_GOP, true, true, false, 0, NULL, 0, 1, false, false},
-    {SV_CODEC_AV1, SV_AUTHENTICITY_LEVEL_FRAME, true, true, false, 0, NULL, 0, 1, false, false},
+    {SV_CODEC_AV1, SV_AUTHENTICITY_LEVEL_GOP, true, false, false, 0, NULL, 0, 1, false, false},
+    {SV_CODEC_AV1, SV_AUTHENTICITY_LEVEL_FRAME, true, false, false, 0, NULL, 0, 1, false, false},
 };
 
 static char private_key_rsa[RSA_PRIVATE_KEY_ALLOC_BYTES];
@@ -388,7 +388,9 @@ get_initialized_signed_video(struct sv_setting settings, bool new_private_key)
   ck_assert_int_eq(signed_video_set_authenticity_level(sv, settings.auth_level), SV_OK);
   ck_assert_int_eq(signed_video_set_max_sei_payload_size(sv, settings.max_sei_payload_size), SV_OK);
   ck_assert_int_eq(signed_video_set_hash_algo(sv, settings.hash_algo_name), SV_OK);
-  ck_assert_int_eq(signed_video_set_sei_epb(sv, settings.ep_before_signing), SV_OK);
+  if (settings.codec != SV_CODEC_AV1) {
+    ck_assert_int_eq(signed_video_set_sei_epb(sv, settings.ep_before_signing), SV_OK);
+  }
   ck_assert_int_eq(signed_video_set_using_golden_sei(sv, settings.with_golden_sei), SV_OK);
 
   if (settings.with_golden_sei) {