diff --git a/libavformat/aacdec.c b/libavformat/aacdec.c
index a476640904..41c9a36239 100644
--- a/libavformat/aacdec.c
+++ b/libavformat/aacdec.c
@@ -146,7 +146,7 @@ static int handle_id3(AVFormatContext *s, AVPacket *pkt)
         return ret;
     }
 
-    ffio_init_context(&pb, pkt->data, pkt->size, 0, NULL, NULL, NULL, NULL);
+    ffio_init_read_context(&pb, pkt->data, pkt->size);
     ff_id3v2_read_dict(&pb.pub, &metadata, ID3v2_DEFAULT_MAGIC, &id3v2_extra_meta);
     if ((ret = ff_id3v2_parse_priv_dict(&metadata, id3v2_extra_meta)) < 0)
         goto error;
diff --git a/libavformat/asfenc.c b/libavformat/asfenc.c
index 244c7e7a27..2f2d9b1bab 100644
--- a/libavformat/asfenc.c
+++ b/libavformat/asfenc.c
@@ -773,8 +773,7 @@ static int asf_write_header(AVFormatContext *s)
     asf->packet_nb_payloads     = 0;
     asf->packet_timestamp_start = -1;
     asf->packet_timestamp_end   = -1;
-    ffio_init_context(&asf->pb, asf->packet_buf, s->packet_size, 1,
-                      NULL, NULL, NULL, NULL);
+    ffio_init_write_context(&asf->pb, asf->packet_buf, s->packet_size);
 
     if (s->avoid_negative_ts < 0)
         s->avoid_negative_ts = 1;
@@ -866,8 +865,7 @@ static void flush_packet(AVFormatContext *s)
     asf->packet_nb_payloads     = 0;
     asf->packet_timestamp_start = -1;
     asf->packet_timestamp_end   = -1;
-    ffio_init_context(&asf->pb, asf->packet_buf, s->packet_size, 1,
-                      NULL, NULL, NULL, NULL);
+    ffio_init_write_context(&asf->pb, asf->packet_buf, s->packet_size);
 }
 
 static void put_payload_header(AVFormatContext *s, ASFStream *stream,
diff --git a/libavformat/av1.c b/libavformat/av1.c
index 4455ec0504..cb86e66d09 100644
--- a/libavformat/av1.c
+++ b/libavformat/av1.c
@@ -107,7 +107,7 @@ int ff_av1_filter_obus_buf(const uint8_t *in, uint8_t **out,
     if (!buf)
         return AVERROR(ENOMEM);
 
-    ffio_init_context(&pb, buf, len, 1, NULL, NULL, NULL, NULL);
+    ffio_init_write_context(&pb, buf, len);
 
     ret = av1_filter_obus(&pb.pub, in, *size, NULL);
     av_assert1(ret == len);
diff --git a/libavformat/av1dec.c b/libavformat/av1dec.c
index 2883b320a1..8a06445958 100644
--- a/libavformat/av1dec.c
+++ b/libavformat/av1dec.c
@@ -167,8 +167,7 @@ static int annexb_probe(const AVProbeData *p)
     int seq = 0;
     int ret, type, cnt = 0;
 
-    ffio_init_context(&ctx, p->buf, p->buf_size, 0,
-                      NULL, NULL, NULL, NULL);
+    ffio_init_read_context(&ctx, p->buf, p->buf_size);
 
     ret = leb(pb, &temporal_unit_size, 1);
     if (ret < 0)
diff --git a/libavformat/avio_internal.h b/libavformat/avio_internal.h
index 1f5e3d474b..57796ade03 100644
--- a/libavformat/avio_internal.h
+++ b/libavformat/avio_internal.h
@@ -93,6 +93,15 @@ void ffio_init_context(FFIOContext *s,
                   int (*write_packet)(void *opaque, uint8_t *buf, int buf_size),
                   int64_t (*seek)(void *opaque, int64_t offset, int whence));
 
+/**
+ * Wrap a buffer in an AVIOContext for reading.
+ */
+void ffio_init_read_context(FFIOContext *s, const uint8_t *buffer, int buffer_size);
+
+/**
+ * Wrap a buffer in an AVIOContext for writing.
+ */
+void ffio_init_write_context(FFIOContext *s, uint8_t *buffer, int buffer_size);
 
 /**
  * Read size bytes from AVIOContext, returning a pointer.
diff --git a/libavformat/aviobuf.c b/libavformat/aviobuf.c
index 4ad734a3c3..029a9e966b 100644
--- a/libavformat/aviobuf.c
+++ b/libavformat/aviobuf.c
@@ -127,6 +127,16 @@ void ffio_init_context(FFIOContext *ctx,
     ctx->short_seek_get      = NULL;
 }
 
+void ffio_init_read_context(FFIOContext *s, const uint8_t *buffer, int buffer_size)
+{
+    ffio_init_context(s, (unsigned char*)buffer, buffer_size, 0, NULL, NULL, NULL, NULL);
+}
+
+void ffio_init_write_context(FFIOContext *s, uint8_t *buffer, int buffer_size)
+{
+    ffio_init_context(s, buffer, buffer_size, 1, NULL, NULL, NULL, NULL);
+}
+
 AVIOContext *avio_alloc_context(
                   unsigned char *buffer,
                   int buffer_size,
diff --git a/libavformat/hls.c b/libavformat/hls.c
index c625e30291..276e4ee333 100644
--- a/libavformat/hls.c
+++ b/libavformat/hls.c
@@ -1265,7 +1265,7 @@ static void intercept_id3(struct playlist *pls, uint8_t *buf,
     if (pls->id3_buf) {
         /* Now parse all the ID3 tags */
         FFIOContext id3ioctx;
-        ffio_init_context(&id3ioctx, pls->id3_buf, id3_buf_pos, 0, NULL, NULL, NULL, NULL);
+        ffio_init_read_context(&id3ioctx, pls->id3_buf, id3_buf_pos);
         handle_id3(&id3ioctx.pub, pls);
     }
 
diff --git a/libavformat/id3v2.c b/libavformat/id3v2.c
index 69193933e0..d83716dcf4 100644
--- a/libavformat/id3v2.c
+++ b/libavformat/id3v2.c
@@ -1001,8 +1001,7 @@ static void id3v2_parse(AVIOContext *pb, AVDictionary **metadata,
                         t++;
                 }
 
-                ffio_init_context(&pb_local, buffer, b - buffer, 0, NULL, NULL, NULL,
-                                  NULL);
+                ffio_init_read_context(&pb_local, buffer, b - buffer);
                 tlen = b - buffer;
                 pbx  = &pb_local.pub; // read from sync buffer
             }
@@ -1038,7 +1037,7 @@ static void id3v2_parse(AVIOContext *pb, AVDictionary **metadata,
                         av_log(s, AV_LOG_ERROR, "Failed to uncompress tag: %d\n", err);
                         goto seek;
                     }
-                    ffio_init_context(&pb_local, uncompressed_buffer, dlen, 0, NULL, NULL, NULL, NULL);
+                    ffio_init_read_context(&pb_local, uncompressed_buffer, dlen);
                     tlen = dlen;
                     pbx = &pb_local.pub; // read from sync buffer
                 }
diff --git a/libavformat/matroskadec.c b/libavformat/matroskadec.c
index 638e07c13d..941c0bcdc9 100644
--- a/libavformat/matroskadec.c
+++ b/libavformat/matroskadec.c
@@ -2599,9 +2599,8 @@ static int mka_parse_audio_codec(MatroskaTrack *track, AVCodecParameters *par,
     if (!strcmp(track->codec_id, "A_MS/ACM") &&
         track->codec_priv.size >= 14) {
         FFIOContext b;
-        ffio_init_context(&b, track->codec_priv.data,
-                            track->codec_priv.size,
-                            0, NULL, NULL, NULL, NULL);
+        ffio_init_read_context(&b, track->codec_priv.data,
+                               track->codec_priv.size);
         ret = ff_get_wav_header(s, &b.pub, par,
                                 track->codec_priv.size, 0);
         if (ret < 0)
@@ -2887,9 +2886,8 @@ static int mkv_parse_video_codec(MatroskaTrack *track, AVCodecParameters *par,
         if (track->codec_priv.size >= 86) {
             FFIOContext b;
             unsigned bit_depth = AV_RB16(track->codec_priv.data + 82);
-            ffio_init_context(&b, track->codec_priv.data,
-                              track->codec_priv.size,
-                              0, NULL, NULL, NULL, NULL);
+            ffio_init_read_context(&b, track->codec_priv.data,
+                                   track->codec_priv.size);
             if (ff_get_qtpalette(codec_id, &b.pub, track->palette)) {
                 bit_depth         &= 0x1F;
                 track->has_palette = 1;
@@ -4057,7 +4055,7 @@ static int matroska_parse_block(MatroskaDemuxContext *matroska, AVBufferRef *buf
 
     av_assert1(buf);
 
-    ffio_init_context(&pb, data, size, 0, NULL, NULL, NULL, NULL);
+    ffio_init_read_context(&pb, data, size);
 
     if ((n = ebml_read_num(matroska, &pb.pub, 8, &num, 1)) < 0)
         return n;
diff --git a/libavformat/mmst.c b/libavformat/mmst.c
index 20b04b12aa..d7f71304e5 100644
--- a/libavformat/mmst.c
+++ b/libavformat/mmst.c
@@ -157,8 +157,8 @@ static int mms_put_utf16(MMSContext *mms, const uint8_t *src)
     FFIOContext bic;
     int size = mms->write_out_ptr - mms->out_buffer;
     int len;
-    ffio_init_context(&bic, mms->write_out_ptr,
-            sizeof(mms->out_buffer) - size, 1, NULL, NULL, NULL, NULL);
+    ffio_init_write_context(&bic, mms->write_out_ptr,
+                            sizeof(mms->out_buffer) - size);
 
     len = avio_put_str16le(&bic.pub, src);
     if (len < 0)
diff --git a/libavformat/mov.c b/libavformat/mov.c
index be9975f297..aa1d9e4ccc 100644
--- a/libavformat/mov.c
+++ b/libavformat/mov.c
@@ -5727,7 +5727,7 @@ static int mov_read_cmov(MOVContext *c, AVIOContext *pb, MOVAtom atom)
     ret = AVERROR_INVALIDDATA;
     if (uncompress (moov_data, (uLongf *) &moov_len, (const Bytef *)cmov_data, cmov_len) != Z_OK)
         goto free_and_return;
-    ffio_init_context(&ctx, moov_data, moov_len, 0, NULL, NULL, NULL, NULL);
+    ffio_init_read_context(&ctx, moov_data, moov_len);
     ctx.pub.seekable = AVIO_SEEKABLE_NORMAL;
     atom.type = MKTAG('m','o','o','v');
     atom.size = moov_len;
diff --git a/libavformat/mpegts.c b/libavformat/mpegts.c
index 8fd1524a8a..d825bf0b5d 100644
--- a/libavformat/mpegts.c
+++ b/libavformat/mpegts.c
@@ -1471,8 +1471,7 @@ static int init_MP4DescrParseContext(MP4DescrParseContext *d, AVFormatContext *s
     if (size > (1 << 30))
         return AVERROR_INVALIDDATA;
 
-    ffio_init_context(&d->pb, (unsigned char *)buf, size,
-                      0, NULL, NULL, NULL, NULL);
+    ffio_init_read_context(&d->pb, buf, size);
 
     d->s               = s;
     d->level           = 0;
@@ -1743,9 +1742,8 @@ static void m4sl_cb(MpegTSFilter *filter, const uint8_t *section,
 
             pes->sl = mp4_descr[i].sl;
 
-            ffio_init_context(&pb, mp4_descr[i].dec_config_descr,
-                              mp4_descr[i].dec_config_descr_len, 0,
-                              NULL, NULL, NULL, NULL);
+            ffio_init_read_context(&pb, mp4_descr[i].dec_config_descr,
+                                   mp4_descr[i].dec_config_descr_len);
             ff_mp4_read_dec_config_descr(s, st, &pb.pub);
             if (st->codecpar->codec_id == AV_CODEC_ID_AAC &&
                 st->codecpar->extradata_size > 0)
@@ -1853,9 +1851,8 @@ int ff_parse_mpeg2_descriptor(AVFormatContext *fc, AVStream *st, int stream_type
             if (mp4_descr[i].dec_config_descr_len &&
                 mp4_descr[i].es_id == desc_es_id) {
                 FFIOContext pb;
-                ffio_init_context(&pb, mp4_descr[i].dec_config_descr,
-                                  mp4_descr[i].dec_config_descr_len, 0,
-                                  NULL, NULL, NULL, NULL);
+                ffio_init_read_context(&pb, mp4_descr[i].dec_config_descr,
+                                       mp4_descr[i].dec_config_descr_len);
                 ff_mp4_read_dec_config_descr(fc, st, &pb.pub);
                 if (st->codecpar->codec_id == AV_CODEC_ID_AAC &&
                     st->codecpar->extradata_size > 0) {
@@ -1875,9 +1872,8 @@ int ff_parse_mpeg2_descriptor(AVFormatContext *fc, AVStream *st, int stream_type
              sti->request_probe > 0) &&
             mp4_descr->dec_config_descr_len && mp4_descr->es_id == pid) {
             FFIOContext pb;
-            ffio_init_context(&pb, mp4_descr->dec_config_descr,
-                              mp4_descr->dec_config_descr_len, 0,
-                              NULL, NULL, NULL, NULL);
+            ffio_init_read_context(&pb, mp4_descr->dec_config_descr,
+                                   mp4_descr->dec_config_descr_len);
             ff_mp4_read_dec_config_descr(fc, st, &pb.pub);
             if (st->codecpar->codec_id == AV_CODEC_ID_AAC &&
                 st->codecpar->extradata_size > 0) {
diff --git a/libavformat/mpjpegdec.c b/libavformat/mpjpegdec.c
index 559a375d8d..f1d2d34689 100644
--- a/libavformat/mpjpegdec.c
+++ b/libavformat/mpjpegdec.c
@@ -120,7 +120,7 @@ static int mpjpeg_read_probe(const AVProbeData *p)
     if (p->buf_size < 2 || p->buf[0] != '-' || p->buf[1] != '-')
         return 0;
 
-    ffio_init_context(&pb, p->buf, p->buf_size, 0, NULL, NULL, NULL, NULL);
+    ffio_init_read_context(&pb, p->buf, p->buf_size);
 
     ret = (parse_multipart_header(&pb.pub, &size, "--", NULL) >= 0) ? AVPROBE_SCORE_MAX : 0;
 
diff --git a/libavformat/oggenc.c b/libavformat/oggenc.c
index 2e582d0754..c669aea25a 100644
--- a/libavformat/oggenc.c
+++ b/libavformat/oggenc.c
@@ -292,7 +292,7 @@ static uint8_t *ogg_write_vorbiscomment(int64_t offset, int bitexact,
     if (!p)
         return NULL;
 
-    ffio_init_context(&pb, p + offset, size - offset, 1, NULL, NULL, NULL, NULL);
+    ffio_init_write_context(&pb, p + offset, size - offset);
     ff_vorbiscomment_write(&pb.pub, *m, vendor, chapters, nb_chapters);
     if (framing_bit)
         avio_w8(&pb.pub, 1);
diff --git a/libavformat/rdt.c b/libavformat/rdt.c
index 2fa3c2d266..b9b02a371f 100644
--- a/libavformat/rdt.c
+++ b/libavformat/rdt.c
@@ -152,8 +152,7 @@ rdt_load_mdpr (PayloadContext *rdt, AVStream *st, int rule_nr)
      */
     if (!rdt->mlti_data)
         return -1;
-    ffio_init_context(&pb0, rdt->mlti_data, rdt->mlti_data_size, 0,
-                  NULL, NULL, NULL, NULL);
+    ffio_init_read_context(&pb0, rdt->mlti_data, rdt->mlti_data_size);
     tag = avio_rl32(pb);
     if (tag == MKTAG('M', 'L', 'T', 'I')) {
         int num, chunk_nr;
@@ -302,7 +301,7 @@ rdt_parse_packet (AVFormatContext *ctx, PayloadContext *rdt, AVStream *st,
         FFIOContext pb;
         int pos, rmflags;
 
-        ffio_init_context(&pb, (uint8_t *)buf, len, 0, NULL, NULL, NULL, NULL);
+        ffio_init_read_context(&pb, buf, len);
         rmflags = (flags & RTP_FLAG_KEY) ? 2 : 0;
         res = ff_rm_parse_packet(rdt->rmctx, &pb.pub, st, rdt->rmst[st->index],
                                  len, pkt, &seq, rmflags, *timestamp);
diff --git a/libavformat/rtpdec_asf.c b/libavformat/rtpdec_asf.c
index 72ead6975a..20ca8295f9 100644
--- a/libavformat/rtpdec_asf.c
+++ b/libavformat/rtpdec_asf.c
@@ -210,7 +210,7 @@ static int asfrtp_parse_packet(AVFormatContext *s, PayloadContext *asf,
 
         av_freep(&asf->buf);
 
-        ffio_init_context(pb0, (uint8_t *)buf, len, 0, NULL, NULL, NULL, NULL);
+        ffio_init_read_context(pb0, buf, len);
 
         while (avio_tell(pb) + 4 < len) {
             int start_off = avio_tell(pb);
diff --git a/libavformat/rtpdec_qt.c b/libavformat/rtpdec_qt.c
index 495a3ec14e..b71055f8b8 100644
--- a/libavformat/rtpdec_qt.c
+++ b/libavformat/rtpdec_qt.c
@@ -85,7 +85,7 @@ static int qt_rtp_parse_packet(AVFormatContext *s, PayloadContext *qt,
     ret = init_get_bits(&gb, buf, len << 3);
     if (ret < 0)
         return ret;
-    ffio_init_context(&pb0, (uint8_t*)buf, len, 0, NULL, NULL, NULL, NULL);
+    ffio_init_read_context(&pb0, buf, len);
 
     if (len < 4)
         return AVERROR_INVALIDDATA;
diff --git a/libavformat/rtsp.c b/libavformat/rtsp.c
index cfafb4be80..c4f78f97b0 100644
--- a/libavformat/rtsp.c
+++ b/libavformat/rtsp.c
@@ -2610,7 +2610,7 @@ static int rtp_read_header(AVFormatContext *s)
         goto fail_nobuf;
     avcodec_parameters_free(&par);
 
-    ffio_init_context(&pb, sdp.str, sdp.len, 0, NULL, NULL, NULL, NULL);
+    ffio_init_read_context(&pb, sdp.str, sdp.len);
     s->pb = &pb.pub;
 
     /* if sdp_read_header() fails then following ff_network_close() cancels out */
diff --git a/libavformat/sapdec.c b/libavformat/sapdec.c
index fd0e662433..59141448f4 100644
--- a/libavformat/sapdec.c
+++ b/libavformat/sapdec.c
@@ -148,8 +148,7 @@ static int sap_read_header(AVFormatContext *s)
     }
 
     av_log(s, AV_LOG_VERBOSE, "SDP:\n%s\n", sap->sdp);
-    ffio_init_context(&sap->sdp_pb, sap->sdp, strlen(sap->sdp), 0, NULL, NULL,
-                  NULL, NULL);
+    ffio_init_read_context(&sap->sdp_pb, sap->sdp, strlen(sap->sdp));
 
     infmt = av_find_input_format("sdp");
     if (!infmt)
diff --git a/libavformat/subtitles.c b/libavformat/subtitles.c
index 6c221e4b29..3413763c7b 100644
--- a/libavformat/subtitles.c
+++ b/libavformat/subtitles.c
@@ -49,9 +49,9 @@ void ff_text_init_avio(void *s, FFTextReader *r, AVIOContext *pb)
                "UTF16 is automatically converted to UTF8, do not specify a character encoding\n");
 }
 
-void ff_text_init_buf(FFTextReader *r, void *buf, size_t size)
+void ff_text_init_buf(FFTextReader *r, const void *buf, size_t size)
 {
-    ffio_init_context(&r->buf_pb, buf, size, 0, NULL, NULL, NULL, NULL);
+    ffio_init_read_context(&r->buf_pb, buf, size);
     ff_text_init_avio(NULL, r, &r->buf_pb.pub);
 }
 
diff --git a/libavformat/subtitles.h b/libavformat/subtitles.h
index f6688b71d7..f4993fe20d 100644
--- a/libavformat/subtitles.h
+++ b/libavformat/subtitles.h
@@ -68,7 +68,7 @@ void ff_text_init_avio(void *s, FFTextReader *r, AVIOContext *pb);
  * @param buf buffer to read from (referenced as long as FFTextReader is in use)
  * @param size size of buf
  */
-void ff_text_init_buf(FFTextReader *r, void *buf, size_t size);
+void ff_text_init_buf(FFTextReader *r, const void *buf, size_t size);
 
 /**
  * Return the byte position of the next byte returned by ff_text_r8(). For
diff --git a/libavformat/vividas.c b/libavformat/vividas.c
index ed4e573df8..2f47d65c7c 100644
--- a/libavformat/vividas.c
+++ b/libavformat/vividas.c
@@ -277,7 +277,8 @@ static uint8_t *read_sb_block(AVIOContext *src, unsigned *size,
     return buf;
 }
 
-static int track_header(VividasDemuxContext *viv, AVFormatContext *s,  uint8_t *buf, int size)
+static int track_header(VividasDemuxContext *viv, AVFormatContext *s,
+                        const uint8_t *buf, int size)
 {
     int i, j, ret;
     int64_t off;
@@ -286,7 +287,7 @@ static int track_header(VividasDemuxContext *viv, AVFormatContext *s,  uint8_t *
     FFIOContext pb0;
     AVIOContext *const pb = &pb0.pub;
 
-    ffio_init_context(&pb0, buf, size, 0, NULL, NULL, NULL, NULL);
+    ffio_init_read_context(&pb0, buf, size);
 
     ffio_read_varlen(pb); // track_header_len
     avio_r8(pb); // '1'
@@ -432,7 +433,8 @@ static int track_header(VividasDemuxContext *viv, AVFormatContext *s,  uint8_t *
     return 0;
 }
 
-static int track_index(VividasDemuxContext *viv, AVFormatContext *s, uint8_t *buf, unsigned size)
+static int track_index(VividasDemuxContext *viv, AVFormatContext *s,
+                       const uint8_t *buf, unsigned size)
 {
     int64_t off;
     int64_t poff;
@@ -443,7 +445,7 @@ static int track_index(VividasDemuxContext *viv, AVFormatContext *s, uint8_t *bu
     int64_t filesize = avio_size(s->pb);
     uint64_t n_sb_blocks_tmp;
 
-    ffio_init_context(&pb0, buf, size, 0, NULL, NULL, NULL, NULL);
+    ffio_init_read_context(&pb0, buf, size);
 
     ffio_read_varlen(pb); // track_index_len
     avio_r8(pb); // 'c'