diff --git a/libavdevice/pulse_audio_enc.c b/libavdevice/pulse_audio_enc.c
index 4955b3b884..3e2cc91f69 100644
--- a/libavdevice/pulse_audio_enc.c
+++ b/libavdevice/pulse_audio_enc.c
@@ -801,5 +801,5 @@ const FFOutputFormat ff_pulse_muxer = {
     .p.flags              = AVFMT_NOFILE,
 #endif
     .p.priv_class         = &pulse_muxer_class,
-    .flags_internal       = FF_FMT_ALLOW_FLUSH,
+    .flags_internal       = FF_OFMT_FLAG_ALLOW_FLUSH,
 };
diff --git a/libavformat/fifo.c b/libavformat/fifo.c
index 2a2673f4d8..23e4149ad6 100644
--- a/libavformat/fifo.c
+++ b/libavformat/fifo.c
@@ -728,5 +728,5 @@ const FFOutputFormat ff_fifo_muxer = {
     .write_packet   = fifo_write_packet,
     .write_trailer  = fifo_write_trailer,
     .deinit         = fifo_deinit,
-    .flags_internal = FF_FMT_ALLOW_FLUSH,
+    .flags_internal = FF_OFMT_FLAG_ALLOW_FLUSH,
 };
diff --git a/libavformat/hlsenc.c b/libavformat/hlsenc.c
index e5350323b1..2202ce64e4 100644
--- a/libavformat/hlsenc.c
+++ b/libavformat/hlsenc.c
@@ -3205,7 +3205,7 @@ const FFOutputFormat ff_hls_muxer = {
     .p.flags          = AVFMT_NOFILE | AVFMT_GLOBALHEADER | AVFMT_NODIMENSIONS,
 #endif
     .p.priv_class     = &hls_class,
-    .flags_internal   = FF_FMT_ALLOW_FLUSH,
+    .flags_internal   = FF_OFMT_FLAG_ALLOW_FLUSH,
     .priv_data_size = sizeof(HLSContext),
     .init           = hls_init,
     .write_header   = hls_write_header,
diff --git a/libavformat/matroskaenc.c b/libavformat/matroskaenc.c
index db41d3d1c2..0de4ec1dc0 100644
--- a/libavformat/matroskaenc.c
+++ b/libavformat/matroskaenc.c
@@ -3569,7 +3569,7 @@ const FFOutputFormat ff_matroska_muxer = {
     .query_codec       = mkv_query_codec,
     .check_bitstream   = mkv_check_bitstream,
     .p.priv_class      = &matroska_webm_class,
-    .flags_internal    = FF_FMT_ALLOW_FLUSH,
+    .flags_internal    = FF_OFMT_FLAG_ALLOW_FLUSH,
 };
 #endif
 
@@ -3606,7 +3606,7 @@ const FFOutputFormat ff_webm_muxer = {
                          AVFMT_TS_NONSTRICT,
 #endif
     .p.priv_class      = &matroska_webm_class,
-    .flags_internal    = FF_FMT_ALLOW_FLUSH,
+    .flags_internal    = FF_OFMT_FLAG_ALLOW_FLUSH,
 };
 #endif
 
@@ -3636,6 +3636,6 @@ const FFOutputFormat ff_matroska_audio_muxer = {
         ff_codec_wav_tags, additional_audio_tags, 0
     },
     .p.priv_class      = &matroska_webm_class,
-    .flags_internal    = FF_FMT_ALLOW_FLUSH,
+    .flags_internal    = FF_OFMT_FLAG_ALLOW_FLUSH,
 };
 #endif
diff --git a/libavformat/movenc.c b/libavformat/movenc.c
index 724a1eb673..127673a9e6 100644
--- a/libavformat/movenc.c
+++ b/libavformat/movenc.c
@@ -8239,7 +8239,7 @@ const FFOutputFormat ff_mov_muxer = {
     },
     .check_bitstream   = mov_check_bitstream,
     .p.priv_class      = &mov_isobmff_muxer_class,
-    .flags_internal    = FF_FMT_ALLOW_FLUSH,
+    .flags_internal    = FF_OFMT_FLAG_ALLOW_FLUSH,
 };
 #endif
 #if CONFIG_TGP_MUXER
@@ -8263,7 +8263,7 @@ const FFOutputFormat ff_tgp_muxer = {
     .p.codec_tag       = codec_3gp_tags_list,
     .check_bitstream   = mov_check_bitstream,
     .p.priv_class      = &mov_isobmff_muxer_class,
-    .flags_internal    = FF_FMT_ALLOW_FLUSH,
+    .flags_internal    = FF_OFMT_FLAG_ALLOW_FLUSH,
 };
 #endif
 #if CONFIG_MP4_MUXER
@@ -8289,7 +8289,7 @@ const FFOutputFormat ff_mp4_muxer = {
     .p.codec_tag       = mp4_codec_tags_list,
     .check_bitstream   = mov_check_bitstream,
     .p.priv_class      = &mov_isobmff_muxer_class,
-    .flags_internal    = FF_FMT_ALLOW_FLUSH,
+    .flags_internal    = FF_OFMT_FLAG_ALLOW_FLUSH,
 };
 #endif
 #if CONFIG_PSP_MUXER
@@ -8314,7 +8314,7 @@ const FFOutputFormat ff_psp_muxer = {
     .p.codec_tag       = mp4_codec_tags_list,
     .check_bitstream   = mov_check_bitstream,
     .p.priv_class      = &mov_isobmff_muxer_class,
-    .flags_internal    = FF_FMT_ALLOW_FLUSH,
+    .flags_internal    = FF_OFMT_FLAG_ALLOW_FLUSH,
 };
 #endif
 #if CONFIG_TG2_MUXER
@@ -8338,7 +8338,7 @@ const FFOutputFormat ff_tg2_muxer = {
     .p.codec_tag       = codec_3gp_tags_list,
     .check_bitstream   = mov_check_bitstream,
     .p.priv_class      = &mov_isobmff_muxer_class,
-    .flags_internal    = FF_FMT_ALLOW_FLUSH,
+    .flags_internal    = FF_OFMT_FLAG_ALLOW_FLUSH,
 };
 #endif
 #if CONFIG_IPOD_MUXER
@@ -8363,7 +8363,7 @@ const FFOutputFormat ff_ipod_muxer = {
     .p.codec_tag       = (const AVCodecTag* const []){ codec_ipod_tags, 0 },
     .check_bitstream   = mov_check_bitstream,
     .p.priv_class      = &mov_isobmff_muxer_class,
-    .flags_internal    = FF_FMT_ALLOW_FLUSH,
+    .flags_internal    = FF_OFMT_FLAG_ALLOW_FLUSH,
 };
 #endif
 #if CONFIG_ISMV_MUXER
@@ -8389,7 +8389,7 @@ const FFOutputFormat ff_ismv_muxer = {
         codec_mp4_tags, codec_ism_tags, 0 },
     .check_bitstream   = mov_check_bitstream,
     .p.priv_class      = &mov_isobmff_muxer_class,
-    .flags_internal    = FF_FMT_ALLOW_FLUSH,
+    .flags_internal    = FF_OFMT_FLAG_ALLOW_FLUSH,
 };
 #endif
 #if CONFIG_F4V_MUXER
@@ -8414,7 +8414,7 @@ const FFOutputFormat ff_f4v_muxer = {
     .p.codec_tag       = (const AVCodecTag* const []){ codec_f4v_tags, 0 },
     .check_bitstream   = mov_check_bitstream,
     .p.priv_class      = &mov_isobmff_muxer_class,
-    .flags_internal    = FF_FMT_ALLOW_FLUSH,
+    .flags_internal    = FF_OFMT_FLAG_ALLOW_FLUSH,
 };
 #endif
 #if CONFIG_AVIF_MUXER
@@ -8437,6 +8437,6 @@ const FFOutputFormat ff_avif_muxer = {
 #endif
     .p.codec_tag       = codec_avif_tags_list,
     .p.priv_class      = &mov_avif_muxer_class,
-    .flags_internal    = FF_FMT_ALLOW_FLUSH,
+    .flags_internal    = FF_OFMT_FLAG_ALLOW_FLUSH,
 };
 #endif
diff --git a/libavformat/mpegtsenc.c b/libavformat/mpegtsenc.c
index b8efc535a7..d8c148bd3c 100644
--- a/libavformat/mpegtsenc.c
+++ b/libavformat/mpegtsenc.c
@@ -2415,6 +2415,6 @@ const FFOutputFormat ff_mpegts_muxer = {
 #else
     .p.flags         = AVFMT_VARIABLE_FPS | AVFMT_NODIMENSIONS,
 #endif
-    .flags_internal  = FF_FMT_ALLOW_FLUSH,
+    .flags_internal  = FF_OFMT_FLAG_ALLOW_FLUSH,
     .p.priv_class   = &mpegts_muxer_class,
 };
diff --git a/libavformat/mux.c b/libavformat/mux.c
index 772f300f16..a2cae97397 100644
--- a/libavformat/mux.c
+++ b/libavformat/mux.c
@@ -1208,10 +1208,10 @@ int av_write_frame(AVFormatContext *s, AVPacket *in)
     if (!in) {
 #if FF_API_ALLOW_FLUSH || LIBAVFORMAT_VERSION_MAJOR >= 61
         // Hint: The pulse audio output device has this set,
-        // so we can't switch the check to FF_FMT_ALLOW_FLUSH immediately.
+        // so we can't switch the check to FF_OFMT_FLAG_ALLOW_FLUSH immediately.
         if (s->oformat->flags & AVFMT_ALLOW_FLUSH) {
 #else
-        if (ffofmt(s->oformat)->flags_internal & FF_FMT_ALLOW_FLUSH) {
+        if (ffofmt(s->oformat)->flags_internal & FF_OFMT_FLAG_ALLOW_FLUSH) {
 #endif
             ret = ffofmt(s->oformat)->write_packet(s, NULL);
             flush_if_needed(s);
diff --git a/libavformat/mux.h b/libavformat/mux.h
index b9ec75641d..bd3eb53380 100644
--- a/libavformat/mux.h
+++ b/libavformat/mux.h
@@ -27,7 +27,15 @@
 
 struct AVDeviceInfoList;
 
-#define FF_FMT_ALLOW_FLUSH                    (1 << 1)
+/**
+ * This flag indicates that the muxer stores data internally
+ * and supports flushing it. Flushing is signalled by sending
+ * a NULL packet to the muxer's write_packet callback;
+ * without this flag, a muxer never receives NULL packets.
+ * So the documentation of write_packet below for the semantics
+ * of the return value in case of flushing.
+ */
+#define FF_OFMT_FLAG_ALLOW_FLUSH                    (1 << 1)
 
 typedef struct FFOutputFormat {
     /**
@@ -40,13 +48,13 @@ typedef struct FFOutputFormat {
     int priv_data_size;
 
     /**
-     * Internal flags. See FF_FMT_* in internal.h and mux.h.
+     * Internal flags. See FF_OFMT_FLAG_* above and FF_FMT_FLAG_* in internal.h.
      */
     int flags_internal;
 
     int (*write_header)(AVFormatContext *);
     /**
-     * Write a packet. If FF_FMT_ALLOW_FLUSH is set in flags_internal,
+     * Write a packet. If FF_OFMT_FLAG_ALLOW_FLUSH is set in flags_internal,
      * pkt can be NULL in order to flush data buffered in the muxer.
      * When flushing, return 0 if there still is more data to flush,
      * or 1 if everything was flushed and there is no more buffered
diff --git a/libavformat/oggenc.c b/libavformat/oggenc.c
index 69a66f586d..bdd19530ce 100644
--- a/libavformat/oggenc.c
+++ b/libavformat/oggenc.c
@@ -777,7 +777,7 @@ const FFOutputFormat ff_ogg_muxer = {
     .p.flags           = AVFMT_TS_NEGATIVE | AVFMT_TS_NONSTRICT,
 #endif
     .p.priv_class      = &ogg_muxer_class,
-    .flags_internal    = FF_FMT_ALLOW_FLUSH,
+    .flags_internal    = FF_OFMT_FLAG_ALLOW_FLUSH,
 };
 #endif
 
@@ -800,7 +800,7 @@ const FFOutputFormat ff_oga_muxer = {
     .p.flags           = AVFMT_TS_NEGATIVE,
 #endif
     .p.priv_class      = &ogg_muxer_class,
-    .flags_internal    = FF_FMT_ALLOW_FLUSH,
+    .flags_internal    = FF_OFMT_FLAG_ALLOW_FLUSH,
 };
 #endif
 
@@ -826,7 +826,7 @@ const FFOutputFormat ff_ogv_muxer = {
     .p.flags           = AVFMT_TS_NEGATIVE | AVFMT_TS_NONSTRICT,
 #endif
     .p.priv_class      = &ogg_muxer_class,
-    .flags_internal    = FF_FMT_ALLOW_FLUSH,
+    .flags_internal    = FF_OFMT_FLAG_ALLOW_FLUSH,
 };
 #endif
 
@@ -849,7 +849,7 @@ const FFOutputFormat ff_spx_muxer = {
     .p.flags           = AVFMT_TS_NEGATIVE,
 #endif
     .p.priv_class      = &ogg_muxer_class,
-    .flags_internal    = FF_FMT_ALLOW_FLUSH,
+    .flags_internal    = FF_OFMT_FLAG_ALLOW_FLUSH,
 };
 #endif
 
@@ -872,6 +872,6 @@ const FFOutputFormat ff_opus_muxer = {
     .p.flags           = AVFMT_TS_NEGATIVE,
 #endif
     .p.priv_class      = &ogg_muxer_class,
-    .flags_internal    = FF_FMT_ALLOW_FLUSH,
+    .flags_internal    = FF_OFMT_FLAG_ALLOW_FLUSH,
 };
 #endif
diff --git a/libavformat/tee.c b/libavformat/tee.c
index a101fede5b..9597137ec2 100644
--- a/libavformat/tee.c
+++ b/libavformat/tee.c
@@ -614,5 +614,5 @@ const FFOutputFormat ff_tee_muxer = {
 #else
     .p.flags           = AVFMT_NOFILE | AVFMT_TS_NEGATIVE,
 #endif
-    .flags_internal    = FF_FMT_ALLOW_FLUSH,
+    .flags_internal    = FF_OFMT_FLAG_ALLOW_FLUSH,
 };
diff --git a/libavformat/tests/fifo_muxer.c b/libavformat/tests/fifo_muxer.c
index 032af07dc9..222761fed3 100644
--- a/libavformat/tests/fifo_muxer.c
+++ b/libavformat/tests/fifo_muxer.c
@@ -159,7 +159,7 @@ const FFOutputFormat ff_fifo_test_muxer = {
 #else
     .p.flags        = AVFMT_NOFILE,
 #endif
-    .flags_internal = FF_FMT_ALLOW_FLUSH,
+    .flags_internal = FF_OFMT_FLAG_ALLOW_FLUSH,
 };
 
 
