diff --git a/tools/pkt-from-core.py b/tools/pkt-from-core.py
index b6cf491594..efc252d369 100755
--- a/tools/pkt-from-core.py
+++ b/tools/pkt-from-core.py
@@ -77,6 +77,7 @@ class BackTrace:
 # Some values from wiretap; wiretap should be a shared
 # libray and a Python module should be created for it so
 # this program could just write a libpcap file directly.
+WTAP_ENCAP_NONE                       = -2
 WTAP_ENCAP_PER_PACKET                 = -1
 WTAP_ENCAP_UNKNOWN                    = 0
 WTAP_ENCAP_ETHERNET                   = 1
@@ -133,6 +134,7 @@ wtap_to_pcap_map = {
 
 
 wtap_name = {
+        WTAP_ENCAP_NONE                       : "None",
         WTAP_ENCAP_UNKNOWN                    : "Unknown",
         WTAP_ENCAP_ETHERNET                   : "Ethernet",
         WTAP_ENCAP_TOKEN_RING                 : "Token-Ring",
diff --git a/tshark.c b/tshark.c
index 93b9029011..b24942e04b 100644
--- a/tshark.c
+++ b/tshark.c
@@ -3623,24 +3623,11 @@ process_cap_file(capture_file *cf, char *save_file, int out_file_type,
     wtap_dump_params params = WTAP_DUMP_PARAMS_INIT;
     char        *shb_user_appl;
     pass_status_t first_pass_status, second_pass_status;
-    gboolean pcapng_pcapng_workaround = false;
-    wtapng_iface_descriptions_t if_tmp;
 
     if (save_file != NULL) {
         /* Set up to write to the capture file. */
         wtap_dump_params_init_no_idbs(&params, cf->provider.wth);
 
-        /* workaround for pcapng -> pcapng (e.g., when pcapng starts with a custom block) */
-        if (out_file_type == wtap_pcapng_file_type_subtype() && params.encap == WTAP_ENCAP_UNKNOWN) {
-            pcapng_pcapng_workaround = true;
-            params.encap = WTAP_ENCAP_PER_PACKET;
-            params.dont_copy_idbs = true; /* make sure this stay true */
-            if (params.idb_inf->interface_data != NULL) {
-                /* lets fake an interface, which is not copied anyway */
-                g_array_insert_val(params.idb_inf->interface_data, 0, if_tmp);
-            }
-        }
-
         /* If we don't have an application name add TShark */
         if (wtap_block_get_string_option_value(g_array_index(params.shb_hdrs, wtap_block_t, 0), OPT_SHB_USERAPPL, &shb_user_appl) != WTAP_OPTTYPE_SUCCESS) {
             /* this is free'd by wtap_block_unref() later */
@@ -3664,11 +3651,6 @@ process_cap_file(capture_file *cf, char *save_file, int out_file_type,
                     &err, &err_info);
         }
 
-        if (pcapng_pcapng_workaround) {
-            /* remove the fake interface before it will be used */
-            g_array_remove_index((params.idb_inf->interface_data), 0);
-        }
-
         g_free(params.idb_inf);
         params.idb_inf = NULL;
 
diff --git a/wiretap/file_access.c b/wiretap/file_access.c
index 54adc1e5d3..795a1ba77e 100644
--- a/wiretap/file_access.c
+++ b/wiretap/file_access.c
@@ -2291,10 +2291,19 @@ wtap_dump_init_dumper(int file_type_subtype, wtap_compression_type compression_t
 				g_array_append_val(wdh->interface_data, descr);
 			}
 		}
-	} else {
+	} else if (params->encap != WTAP_ENCAP_NONE) {
 		int snaplen;
 
-		// XXX IDBs should be optional.
+		// Generate a fake IDB if we don't have one, unless the
+		// file encapsulation is none. (WTAP_ENCAP_NONE either
+		// means that there are no interfaces, or they will be
+		// provided later when reading the file in single-pass mode.)
+		//
+		// XXX File types should provide their own IDBs (possibly
+		// fake ones generated by wtap_add_generated_idb()), in
+		// order to support being used as inputs for mergecap where
+		// pcapng is the output. This doesn't work for files with
+		// WTAP_ENCAP_PER_PACKET.
 		descr = wtap_block_create(WTAP_BLOCK_IF_ID_AND_INFO);
 		descr_mand = (wtapng_if_descr_mandatory_t*)wtap_block_get_mandatory_data(descr);
 		descr_mand->wtap_encap = params->encap;
diff --git a/wiretap/introspection-enums.c b/wiretap/introspection-enums.c
index f030f7738b..6fe474605a 100644
--- a/wiretap/introspection-enums.c
+++ b/wiretap/introspection-enums.c
@@ -269,6 +269,7 @@ static ws_enum_t all_enums[] = {
     ENUM(WTAP_ENCAP_ATM_PDUS),
     ENUM(WTAP_ENCAP_ATM_PDUS_UNTRUNCATED),
     ENUM(WTAP_ENCAP_ATM_RFC1483),
+    ENUM(WTAP_ENCAP_ATSC_ALP),
     ENUM(WTAP_ENCAP_AUERSWALD_LOG),
     ENUM(WTAP_ENCAP_AUTOSAR_DLT),
     ENUM(WTAP_ENCAP_AX25),
@@ -408,6 +409,7 @@ static ws_enum_t all_enums[] = {
     ENUM(WTAP_ENCAP_NETTL_X25),
     ENUM(WTAP_ENCAP_NFC_LLCP),
     ENUM(WTAP_ENCAP_NFLOG),
+    ENUM(WTAP_ENCAP_NONE),
     ENUM(WTAP_ENCAP_NORDIC_BLE),
     ENUM(WTAP_ENCAP_NSTRACE_1_0),
     ENUM(WTAP_ENCAP_NSTRACE_2_0),
diff --git a/wiretap/pcapng.c b/wiretap/pcapng.c
index 6cd40f2564..4ed6c5a23c 100644
--- a/wiretap/pcapng.c
+++ b/wiretap/pcapng.c
@@ -1621,7 +1621,7 @@ pcapng_read_if_descr_block(wtap *wth, FILE_T fh, pcapng_block_header_t *bh,
      * so it probably doesn't have a single encapsulation for all
      * packets in the file.
      */
-    if (wth->file_encap == WTAP_ENCAP_UNKNOWN) {
+    if (wth->file_encap == WTAP_ENCAP_NONE) {
         wth->file_encap = if_descr_mand->wtap_encap;
     } else {
         if (wth->file_encap != if_descr_mand->wtap_encap) {
@@ -3097,7 +3097,7 @@ pcapng_read_systemd_journal_export_block(wtap *wth, FILE_T fh, pcapng_block_head
      */
     wblock->internal = FALSE;
 
-    if (wth->file_encap == WTAP_ENCAP_UNKNOWN) {
+    if (wth->file_encap == WTAP_ENCAP_NONE) {
         /*
          * Nothing (most notably an IDB) has set a file encap at this point.
          * Do so here.
@@ -3666,7 +3666,7 @@ pcapng_open(wtap *wth, int *err, gchar **err_info)
     wtap_block_unref(wblock.block);
     wblock.block = NULL;
 
-    wth->file_encap = WTAP_ENCAP_UNKNOWN;
+    wth->file_encap = WTAP_ENCAP_NONE;
     wth->snapshot_length = 0;
     wth->file_tsprec = WTAP_TSPREC_UNKNOWN;
     pcapng = g_new(pcapng_t, 1);
@@ -6323,6 +6323,10 @@ static int pcapng_dump_can_write_encap(int wtap_encap)
     if (wtap_encap == WTAP_ENCAP_PER_PACKET)
         return 0;
 
+    /* No encapsulation type (yet) is supported. */
+    if (wtap_encap == WTAP_ENCAP_NONE)
+        return 0;
+
     /* Is it a filetype-specific encapsulation that we support? */
     if (pcapng_encap_is_ft_specific(wtap_encap)) {
         return 0;
diff --git a/wiretap/wtap.c b/wiretap/wtap.c
index d18ff3dcad..7e485cc4a5 100644
--- a/wiretap/wtap.c
+++ b/wiretap/wtap.c
@@ -212,7 +212,8 @@ wtap_add_generated_idb(wtap *wth)
 	int snaplen;
 
 	ws_assert(wth->file_encap != WTAP_ENCAP_UNKNOWN &&
-	    wth->file_encap != WTAP_ENCAP_PER_PACKET);
+	    wth->file_encap != WTAP_ENCAP_PER_PACKET &&
+	    wth->file_encap != WTAP_ENCAP_NONE);
 	ws_assert(wth->file_tsprec != WTAP_TSPREC_UNKNOWN &&
 	    wth->file_tsprec != WTAP_TSPREC_PER_PACKET);
 
@@ -1249,8 +1250,10 @@ wtap_register_encap_type(const char *description, const char *name)
 const char *
 wtap_encap_name(int encap)
 {
-	if (encap < WTAP_ENCAP_PER_PACKET || encap >= WTAP_NUM_ENCAP_TYPES)
+	if (encap < WTAP_ENCAP_NONE || encap >= WTAP_NUM_ENCAP_TYPES)
 		return "illegal";
+	else if (encap == WTAP_ENCAP_NONE)
+		return "none";
 	else if (encap == WTAP_ENCAP_PER_PACKET)
 		return "per-packet";
 	else
@@ -1261,8 +1264,10 @@ wtap_encap_name(int encap)
 const char *
 wtap_encap_description(int encap)
 {
-	if (encap < WTAP_ENCAP_PER_PACKET || encap >= WTAP_NUM_ENCAP_TYPES)
+	if (encap < WTAP_ENCAP_NONE || encap >= WTAP_NUM_ENCAP_TYPES)
 		return "Illegal";
+	else if (encap == WTAP_ENCAP_NONE)
+		return "None";
 	else if (encap == WTAP_ENCAP_PER_PACKET)
 		return "Per packet";
 	else
@@ -1665,6 +1670,7 @@ wtap_read(wtap *wth, wtap_rec *rec, Buffer *buf, int *err,
 		 * encapsulation type.
 		 */
 		ws_assert(rec->rec_header.packet_header.pkt_encap != WTAP_ENCAP_PER_PACKET);
+		ws_assert(rec->rec_header.packet_header.pkt_encap != WTAP_ENCAP_NONE);
 	}
 
 	return TRUE;	/* success */
@@ -1821,6 +1827,7 @@ wtap_seek_read(wtap *wth, gint64 seek_off, wtap_rec *rec, Buffer *buf,
 		 * encapsulation type.
 		 */
 		ws_assert(rec->rec_header.packet_header.pkt_encap != WTAP_ENCAP_PER_PACKET);
+		ws_assert(rec->rec_header.packet_header.pkt_encap != WTAP_ENCAP_NONE);
 	}
 
 	return TRUE;
diff --git a/wiretap/wtap.h b/wiretap/wtap.h
index d2e911e60b..6fa47a5cd0 100644
--- a/wiretap/wtap.h
+++ b/wiretap/wtap.h
@@ -31,7 +31,17 @@ extern "C" {
  * don't have a single encapsulation type for all packets in the file.
  *
  * WTAP_ENCAP_UNKNOWN is returned by "wtap_pcap_encap_to_wtap_encap()"
- * if it's handed an unknown encapsulation.
+ * if it's handed an unknown encapsulation. It is also used by file
+ * types for encapsulations which are unsupported by libwiretap.
+ *
+ * WTAP_ENCAP_NONE is an initial value used by file types like pcapng
+ * that do not have a single file level encapsulation type. If and when
+ * something that indicate encapsulation is read, the encapsulation will
+ * change (possibly to WTAP_ENCAP_PER_PACKET) and appropriate IDBs will
+ * be generated. If a file type uses this value, it MUST provide IDBs
+ * (possibly fake) when the encapsulation changes; otherwise, it should
+ * return WTAP_ENCAP_UNKNOWN so that attempts to write an output file
+ * without reading the entire input file first fail gracefully.
  *
  * WTAP_ENCAP_FDDI_BITSWAPPED is for FDDI captures on systems where the
  * MAC addresses you get from the hardware are bit-swapped.  Ideally,
@@ -74,6 +84,7 @@ extern "C" {
  *     what older versions of "libpcap" on Linux turn the Ethernet
  *     header for loopback interfaces into (0.6.0 and later versions
  *     leave the Ethernet header alone and make it DLT_EN10MB). */
+#define WTAP_ENCAP_NONE                         -2
 #define WTAP_ENCAP_PER_PACKET                   -1
 #define WTAP_ENCAP_UNKNOWN                        0
 #define WTAP_ENCAP_ETHERNET                       1