diff --git a/Changelog b/Changelog
index 30a8978db4..0ff62ff69d 100644
--- a/Changelog
+++ b/Changelog
@@ -48,6 +48,7 @@ version <next>:
 - drmeter audio filter
 - hapqa_extract bitstream filter
 - filter_units bitstream filter
+- segafilm muxer
 
 
 version 3.4:
diff --git a/libavformat/Makefile b/libavformat/Makefile
index 39ec68c28b..4abb992b14 100644
--- a/libavformat/Makefile
+++ b/libavformat/Makefile
@@ -462,6 +462,7 @@ OBJS-$(CONFIG_SDR2_DEMUXER)              += sdr2.o
 OBJS-$(CONFIG_SDS_DEMUXER)               += sdsdec.o
 OBJS-$(CONFIG_SDX_DEMUXER)               += sdxdec.o
 OBJS-$(CONFIG_SEGAFILM_DEMUXER)          += segafilm.o
+OBJS-$(CONFIG_SEGAFILM_MUXER)            += segafilmenc.o
 OBJS-$(CONFIG_SEGMENT_MUXER)             += segment.o
 OBJS-$(CONFIG_SHORTEN_DEMUXER)           += shortendec.o rawdec.o
 OBJS-$(CONFIG_SIFF_DEMUXER)              += siff.o
diff --git a/libavformat/allformats.c b/libavformat/allformats.c
index 9dc5ce8a76..dfd964f07a 100644
--- a/libavformat/allformats.c
+++ b/libavformat/allformats.c
@@ -364,6 +364,7 @@ extern AVInputFormat  ff_sdr2_demuxer;
 extern AVInputFormat  ff_sds_demuxer;
 extern AVInputFormat  ff_sdx_demuxer;
 extern AVInputFormat  ff_segafilm_demuxer;
+extern AVOutputFormat ff_segafilm_muxer;
 extern AVOutputFormat ff_segment_muxer;
 extern AVOutputFormat ff_stream_segment_muxer;
 extern AVInputFormat  ff_shorten_demuxer;
diff --git a/libavformat/segafilmenc.c b/libavformat/segafilmenc.c
new file mode 100644
index 0000000000..cc0e21d4d3
--- /dev/null
+++ b/libavformat/segafilmenc.c
@@ -0,0 +1,380 @@
+/*
+ * Cinepak Video Decoder
+ * Copyright (C) 2003 The FFmpeg project
+ *
+ * This file is part of FFmpeg.
+ *
+ * FFmpeg is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * FFmpeg is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with FFmpeg; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+/**
+ * @file
+ * Sega FILM (.cpk) file muxer
+ * @author Misty De Meo <misty@brew.sh>
+ *
+ * @see For more information regarding the Sega FILM file format, visit:
+ *   http://wiki.multimedia.cx/index.php?title=Sega_FILM
+ */
+
+#include "libavutil/intreadwrite.h"
+#include "avformat.h"
+#include "internal.h"
+#include "avio_internal.h"
+
+typedef struct FILMPacket {
+    int audio;
+    int keyframe;
+    int32_t pts;
+    int32_t duration;
+    int32_t size;
+    int32_t index;
+    struct FILMPacket *next;
+} FILMPacket;
+
+typedef struct FILMOutputContext {
+    const AVClass *class;
+    int audio_index;
+    int video_index;
+    int64_t stab_pos;
+    FILMPacket *start;
+    FILMPacket *last;
+    int64_t packet_count;
+} FILMOutputContext;
+
+static int film_write_packet_to_header(AVFormatContext *format_context, FILMPacket *pkt)
+{
+    AVIOContext *pb = format_context->pb;
+    // The bits in these two 32-bit integers contain info about the contents of this sample
+    int32_t info1 = 0;
+    int32_t info2 = 0;
+
+    if (pkt->audio) {
+        // Always the same, carries no more information than "this is audio"
+        info1 = 0xFFFFFFFF;
+        info2 = 1;
+    } else {
+        info1 = pkt->pts;
+        info2 = pkt->duration;
+        // The top bit being set indicates a key frame
+        if (pkt->keyframe)
+            info1 |= (1 << 31);
+    }
+
+    // Write the 16-byte sample info packet to the STAB chunk in the header
+    avio_wb32(pb, pkt->index);
+    avio_wb32(pb, pkt->size);
+    avio_wb32(pb, info1);
+    avio_wb32(pb, info2);
+
+    return 0;
+}
+
+static int film_write_packet(AVFormatContext *format_context, AVPacket *pkt)
+{
+    FILMPacket *metadata = av_mallocz(sizeof(FILMPacket));
+    if (!metadata)
+        return AVERROR(ENOMEM);
+    AVIOContext *pb = format_context->pb;
+    FILMOutputContext *film = format_context->priv_data;
+    int encoded_buf_size = 0;
+
+    // Track the metadata used to write the header and add it to the linked list
+    metadata->audio = pkt->stream_index == film->audio_index;
+    metadata->keyframe = pkt->flags & AV_PKT_FLAG_KEY;
+    metadata->pts = pkt->pts;
+    metadata->duration = pkt->duration;
+    metadata->size = pkt->size;
+    if (film->last == NULL) {
+        metadata->index = 0;
+    } else {
+        metadata->index = film->last->index + film->last->size;
+        film->last->next = metadata;
+    }
+    metadata->next = NULL;
+    if (film->start == NULL)
+        film->start = metadata;
+    film->packet_count++;
+    film->last = metadata;
+
+    /* Sega Cinepak has an extra two-byte header; write dummy data there,
+     * then adjust the cvid header to accommodate for the extra size */
+    if (!metadata->audio) {
+        encoded_buf_size = AV_RB24(&pkt->data[1]);
+        // Already Sega Cinepak, so no need to reformat the packets
+        if (encoded_buf_size != pkt->size && (pkt->size % encoded_buf_size) != 0) {
+            avio_write(pb, pkt->data, pkt->size);
+        } else {
+            /* In Sega Cinepak, the reported size in the Cinepak header is
+             * 8 bytes too short. However, the size in the STAB section of the header
+             * is correct, taking into account the extra two bytes. */
+            AV_WB24(&pkt->data[1], pkt->size - 8 + 2);
+            metadata->size += 2;
+            uint8_t padding[2] = {0, 0};
+
+            avio_write(pb, pkt->data, 10);
+            avio_write(pb, padding, 2);
+            avio_write(pb, &pkt->data[10], pkt->size - 10);
+        }
+    } else {
+        // Audio can just be written as-is
+        avio_write(pb, pkt->data, pkt->size);
+    }
+
+    return 0;
+}
+
+static int get_audio_codec_id(enum AVCodecID codec_id)
+{
+    // 0 (PCM) and 2 (ADX) are the only known values
+    switch (codec_id) {
+    case AV_CODEC_ID_PCM_S8:
+    case AV_CODEC_ID_PCM_S8_PLANAR:
+    case AV_CODEC_ID_PCM_S16BE_PLANAR:
+        return 0;
+        break;
+    case AV_CODEC_ID_ADPCM_ADX:
+        return 2;
+        break;
+    default:
+        return -1;
+    }
+}
+
+static int film_init(AVFormatContext *format_context)
+{
+    FILMOutputContext *film = format_context->priv_data;
+    film->audio_index = -1;
+    film->video_index = -1;
+    film->stab_pos = 0;
+    film->packet_count = 0;
+    film->start = NULL;
+    film->last = NULL;
+
+    AVStream *audio = NULL;
+
+    for (int i = 0; i < format_context->nb_streams; i++) {
+        AVStream *st = format_context->streams[i];
+        if (st->codecpar->codec_type == AVMEDIA_TYPE_AUDIO) {
+            if (film->audio_index > -1) {
+                av_log(format_context, AV_LOG_ERROR, "Sega FILM allows a maximum of one audio stream.\n");
+                return AVERROR(EINVAL);
+            }
+            film->audio_index = i;
+            audio = st;
+        }
+
+        if (st->codecpar->codec_type == AVMEDIA_TYPE_VIDEO) {
+            if (film->video_index > -1) {
+                av_log(format_context, AV_LOG_ERROR, "Sega FILM allows a maximum of one video stream.\n");
+                return AVERROR(EINVAL);
+            }
+            film->video_index = i;
+        }
+
+        if (film->video_index == -1) {
+            av_log(format_context, AV_LOG_ERROR, "No video stream present.\n");
+            return AVERROR(EINVAL);
+        }
+    }
+
+    if (audio != NULL && get_audio_codec_id(audio->codecpar->codec_id) < 0) {
+        av_log(format_context, AV_LOG_ERROR, "Incompatible audio stream format.\n");
+        return AVERROR(EINVAL);
+    }
+
+    return 0;
+}
+
+static int shift_data(AVFormatContext *format_context, int64_t shift_size)
+{
+    int ret = 0;
+    int64_t pos, pos_end = avio_tell(format_context->pb);
+    uint8_t *buf, *read_buf[2];
+    int read_buf_id = 0;
+    int read_size[2];
+    AVIOContext *read_pb;
+
+    buf = av_malloc(shift_size * 2);
+    if (!buf)
+        return AVERROR(ENOMEM);
+    read_buf[0] = buf;
+    read_buf[1] = buf + shift_size;
+
+    /* Write the header at the beginning of the file, shifting all content as necessary;
+     * based on the approach used by MOV faststart. */
+    avio_flush(format_context->pb);
+    ret = format_context->io_open(format_context, &read_pb, format_context->url, AVIO_FLAG_READ, NULL);
+    if (ret < 0) {
+        av_log(format_context, AV_LOG_ERROR, "Unable to re-open %s output file to "
+               "write the header\n", format_context->url);
+        av_free(buf);
+        return ret;
+    }
+
+    /* mark the end of the shift to up to the last data we wrote, and get ready
+     * for writing */
+    pos_end = avio_tell(format_context->pb);
+    avio_seek(format_context->pb, shift_size, SEEK_SET);
+
+    /* start reading at where the new header will be placed */
+    avio_seek(read_pb, 0, SEEK_SET);
+    pos = avio_tell(read_pb);
+
+#define READ_BLOCK do {                                                             \
+    read_size[read_buf_id] = avio_read(read_pb, read_buf[read_buf_id], shift_size);  \
+    read_buf_id ^= 1;                                                               \
+} while (0)
+
+    /* shift data by chunk of at most shift_size */
+    READ_BLOCK;
+    do {
+        int n;
+        READ_BLOCK;
+        n = read_size[read_buf_id];
+        if (n <= 0)
+            break;
+        avio_write(format_context->pb, read_buf[read_buf_id], n);
+        pos += n;
+    } while (pos < pos_end);
+    ff_format_io_close(format_context, &read_pb);
+
+    av_free(buf);
+    return 0;
+}
+
+static int film_write_header(AVFormatContext *format_context)
+{
+    int ret = 0;
+    int64_t stabstart_pos, sample_table_size, stabsize, headersize;
+    int8_t audio_codec;
+    AVIOContext *pb = format_context->pb;
+    FILMOutputContext *film = format_context->priv_data;
+    FILMPacket *prev, *packet;
+    AVStream *audio = NULL;
+    AVStream *video = NULL;
+
+    /* Calculate how much we need to reserve for the header;
+     * this is the amount the rest of the data will be shifted up by. */
+    sample_table_size = film->packet_count * 16;
+    stabsize = 16 + sample_table_size;
+    headersize = 16 + // FILM header base
+                 32 + // FDSC chunk
+                 stabsize;
+
+    ret = shift_data(format_context, headersize);
+    if (ret < 0)
+        return ret;
+    // Seek back to the beginning to start writing the header now
+    avio_seek(pb, 0, SEEK_SET);
+
+    if (film->audio_index > -1)
+        audio = format_context->streams[film->audio_index];
+    if (film->video_index > -1)
+        video = format_context->streams[film->video_index];
+
+    if (audio != NULL) {
+        audio_codec = get_audio_codec_id(audio->codecpar->codec_id);
+        if (audio_codec < 0) {
+            av_log(format_context, AV_LOG_ERROR, "Incompatible audio stream format.\n");
+            return AVERROR(EINVAL);
+        }
+    }
+
+    // First, write the FILM header; this is very simple
+
+    ffio_wfourcc(pb, "FILM");
+    avio_wb32(pb, 48 + stabsize);
+    /* This seems to be okay to hardcode, since this muxer targets 1.09 features;
+     * videos produced by this muxer are readable by 1.08 and lower players. */
+    ffio_wfourcc(pb, "1.09");
+    // I have no idea what this field does, might be reserved
+    avio_wb32(pb, 0);
+
+    // Next write the FDSC (file description) chunk
+    ffio_wfourcc(pb, "FDSC");
+    avio_wb32(pb, 0x20); // Size of FDSC chunk
+    // TODO stop hardcoding this if support for another codec is added
+    ffio_wfourcc(pb, "cvid");
+    avio_wb32(pb, video->codecpar->height);
+    avio_wb32(pb, video->codecpar->width);
+    avio_w8(pb, 24); // Bits per pixel - observed to always be 24
+
+    if (audio != NULL) {
+        avio_w8(pb, audio->codecpar->channels); // Audio channels
+        avio_w8(pb, audio->codecpar->bits_per_coded_sample); // Audio bit depth
+        avio_w8(pb, audio_codec); // Compression - 0 is PCM, 2 is ADX
+        avio_wb16(pb, audio->codecpar->sample_rate); // Audio sampling rate
+    } else {
+        // Set all these fields to 0 if there's no audio
+        avio_w8(pb, 0);
+        avio_w8(pb, 0);
+        avio_w8(pb, 0);
+        avio_wb16(pb, 0);
+    }
+
+    // I have no idea what this pair of fields does either, might be reserved
+    avio_wb32(pb, 0);
+    avio_wb16(pb, 0);
+
+    // Finally, write the STAB (sample table) chunk
+    stabstart_pos = avio_tell(pb);
+    ffio_wfourcc(pb, "STAB");
+    avio_wb32(pb, 16 + (film->packet_count * 16));
+    /* Framerate base frequency. Here we're assuming that the frame rate is even.
+     * In real world Sega FILM files, there are usually a couple of approaches:
+     * a) framerate base frequency is the same as the framerate, and ticks
+     *    increment by 1 every frame, or
+     * b) framerate base frequency is a much larger number, and ticks
+     *    increment by larger steps every frame.
+     * The latter occurs even in cases where the frame rate is even; for example, in
+     * Lunar: Silver Star Story, the base frequency is 600 and each frame, the ticks
+     * are incremented by 25 for an evenly spaced framerate of 24fps. */
+    avio_wb32(pb, av_q2d(av_inv_q(video->time_base)));
+
+    avio_wb32(pb, film->packet_count);
+
+    avio_flush(pb);
+
+    // Finally, write out each packet's data to the header
+    packet = film->start;
+    while (packet != NULL)
+    {
+        film_write_packet_to_header(format_context, packet);
+        prev = packet;
+        packet = packet->next;
+        av_freep(&prev);
+    }
+
+    return 0;
+}
+
+static const AVClass film_muxer_class = {
+    .class_name     = "Sega FILM muxer",
+    .item_name      = av_default_item_name,
+    .version        = LIBAVUTIL_VERSION_INT,
+};
+
+AVOutputFormat ff_segafilm_muxer = {
+    .name           = "film_cpk",
+    .long_name      = NULL_IF_CONFIG_SMALL("Sega FILM / CPK"),
+    .extensions     = "cpk",
+    .priv_data_size = sizeof(FILMOutputContext),
+    .audio_codec    = AV_CODEC_ID_PCM_S16BE_PLANAR,
+    .video_codec    = AV_CODEC_ID_CINEPAK,
+    .init           = film_init,
+    .write_trailer  = film_write_header,
+    .write_packet   = film_write_packet,
+    .priv_class     = &film_muxer_class,
+};
