diff --git a/MAINTAINERS b/MAINTAINERS
index e49cb0fb3a..d811548f4c 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -191,6 +191,7 @@ Muxers/Demuxers:
   flic.c                                Mike Melanson
   flvdec.c, flvenc.c                    Michael Niedermayer
   gxf.c                                 Reimar Doeffinger
+  gxfenc.c                              Baptiste Coudurier
   idcin.c                               Mike Melanson
   idroq.c                               Mike Melanson
   ipmovie.c                             Mike Melanson
diff --git a/libavformat/Makefile b/libavformat/Makefile
index 00141e818e..fb660fd973 100644
--- a/libavformat/Makefile
+++ b/libavformat/Makefile
@@ -183,6 +183,10 @@ ifeq ($(CONFIG_LIBOGG),yes)
 OBJS-$(CONFIG_OGG_MUXER)                 += ogg.o
 endif
 
+ifeq ($(CONFIG_GPL),yes)
+OBJS-$(CONFIG_GXF_MUXER)                 += gxfenc.o
+endif
+
 OBJS += $(OBJS-yes)
 
 NAME=avformat
diff --git a/libavformat/allformats.c b/libavformat/allformats.c
index 3ce379313e..3ff29fe5b6 100644
--- a/libavformat/allformats.c
+++ b/libavformat/allformats.c
@@ -138,6 +138,9 @@ void av_register_all(void)
 #ifdef CONFIG_GXF_DEMUXER
     av_register_input_format(&gxf_demuxer);
 #endif
+#if defined(CONFIG_GXF_MUXER) && defined(CONFIG_GPL)
+    av_register_output_format(&gxf_muxer);
+#endif
 #ifdef CONFIG_IDCIN_DEMUXER
     av_register_input_format(&idcin_demuxer);
 #endif
diff --git a/libavformat/allformats.h b/libavformat/allformats.h
index 18b2832857..f26375451c 100644
--- a/libavformat/allformats.h
+++ b/libavformat/allformats.h
@@ -35,6 +35,7 @@ extern AVInputFormat gif_demuxer;
 extern AVInputFormat video_grab_device_demuxer;
 extern AVInputFormat video_grab_device_demuxer;
 extern AVInputFormat gxf_demuxer;
+extern AVOutputFormat gxf_muxer;
 extern AVInputFormat idcin_demuxer;
 extern AVInputFormat roq_demuxer;
 extern AVInputFormat image2_demuxer;
diff --git a/libavformat/gxf.h b/libavformat/gxf.h
new file mode 100644
index 0000000000..b23dfd86a0
--- /dev/null
+++ b/libavformat/gxf.h
@@ -0,0 +1,13 @@
+#ifndef FFMPEG_GXF_H
+#define FFMPEG_GXF_H
+
+/* gxf.c */
+typedef enum {
+    PKT_MAP = 0xbc,
+    PKT_MEDIA = 0xbf,
+    PKT_EOS = 0xfb,
+    PKT_FLT = 0xfc,
+    PKT_UMF = 0xfd
+} pkt_type_t;
+
+#endif /* FFMPEG_GXF_H */
diff --git a/libavformat/gxfenc.c b/libavformat/gxfenc.c
new file mode 100644
index 0000000000..480821b3ef
--- /dev/null
+++ b/libavformat/gxfenc.c
@@ -0,0 +1,823 @@
+/*
+ * GXF muxer.
+ * Copyright (c) 2006 SmartJog S.A., Baptiste Coudurier <baptiste dot coudurier at smartjog dot com>.
+ *
+ * This library is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This library 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
+ */
+
+#include "avformat.h"
+#include "gxf.h"
+#include "riff.h"
+
+#define GXF_AUDIO_PACKET_SIZE 65536
+
+typedef struct GXFStreamContext {
+    AVCodecContext *codec;
+    FifoBuffer audio_buffer;
+    uint32_t track_type;
+    uint32_t sample_size;
+    uint32_t sample_rate;
+    uint16_t media_type;
+    uint16_t media_info;
+    uint8_t index;
+    int frame_rate_index;
+    int lines_index;
+    int fields;
+    int iframes;
+    int pframes;
+    int bframes;
+    int p_per_gop;
+    int b_per_gop;
+} GXFStreamContext;
+
+typedef struct GXFContext {
+    uint32_t nb_frames;
+    uint32_t material_flags;
+    uint16_t audio_tracks;
+    uint16_t mpeg_tracks;
+    int64_t creation_time;
+    uint32_t umf_start_offset;
+    uint32_t umf_track_offset;
+    uint32_t umf_media_offset;
+    uint32_t umf_user_data_offset;
+    uint32_t umf_user_data_size;
+    uint32_t umf_length;
+    uint16_t umf_track_size;
+    uint16_t umf_media_size;
+    int audio_written;
+    int sample_rate;
+    int field_number;
+    int flags;
+    AVFormatContext *fc;
+    GXFStreamContext streams[48];
+} GXFContext;
+
+typedef struct GXF_Lines {
+    int height;
+    int index;
+} GXF_Lines;
+
+
+/* FIXME check if it is relevant */
+static const GXF_Lines gxf_lines_tab[] = {
+    { 480,  1 }, /* NTSC */
+    { 512,  1 }, /* NTSC + VBI */
+    { 576,  2 }, /* PAL */
+    { 608,  2 }, /* PAL + VBI */
+    { 1080, 4 },
+    { 720,  6 },
+};
+
+static const CodecTag gxf_media_types[] = {
+    { CODEC_ID_MJPEG     ,   3 }, /* NTSC */
+    { CODEC_ID_MJPEG     ,   4 }, /* PAL */
+    { CODEC_ID_PCM_S24LE ,   9 },
+    { CODEC_ID_PCM_S16LE ,  10 },
+    { CODEC_ID_MPEG2VIDEO,  11 }, /* NTSC */
+    { CODEC_ID_MPEG2VIDEO,  12 }, /* PAL */
+    { CODEC_ID_DVVIDEO   ,  13 }, /* NTSC */
+    { CODEC_ID_DVVIDEO   ,  14 }, /* PAL */
+    { CODEC_ID_DVVIDEO   ,  15 }, /* 50M NTSC */
+    { CODEC_ID_DVVIDEO   ,  16 }, /* 50M PAL */
+    { CODEC_ID_AC3       ,  17 },
+    //{ CODEC_ID_NONE,  ,   18 }, /* Non compressed 24 bit audio */
+    { CODEC_ID_MPEG2VIDEO,  20 }, /* MPEG HD */
+    { CODEC_ID_MPEG1VIDEO,  22 }, /* NTSC */
+    { CODEC_ID_MPEG1VIDEO,  23 }, /* PAL */
+    { 0, 0 },
+};
+
+#define SERVER_PATH "/space/"
+#define ES_NAME_PATTERN "ES."
+
+static int gxf_find_lines_index(GXFStreamContext *ctx)
+{
+    int i;
+
+    for (i = 0; i < 6; ++i) {
+        if (ctx->codec->height == gxf_lines_tab[i].height) {
+            ctx->lines_index = gxf_lines_tab[i].index;
+            return 0;
+        }
+    }
+    return -1;
+}
+
+static void gxf_write_padding(ByteIOContext *pb, offset_t to_pad)
+{
+    while (to_pad--) {
+        put_byte(pb, 0);
+    }
+}
+
+static offset_t updatePacketSize(ByteIOContext *pb, offset_t pos)
+{
+    offset_t curpos;
+    int size;
+
+    size = url_ftell(pb) - pos;
+    if (size % 4) {
+        gxf_write_padding(pb, 4 - size % 4);
+        size = url_ftell(pb) - pos;
+    }
+    curpos = url_ftell(pb);
+    url_fseek(pb, pos + 6, SEEK_SET);
+    put_be32(pb, size);
+    url_fseek(pb, curpos, SEEK_SET);
+    return curpos - pos;
+}
+
+static offset_t updateSize(ByteIOContext *pb, offset_t pos)
+{
+    offset_t curpos;
+
+    curpos = url_ftell(pb);
+    url_fseek(pb, pos, SEEK_SET);
+    put_be16(pb, curpos - pos - 2);
+    url_fseek(pb, curpos, SEEK_SET);
+    return curpos - pos;
+}
+
+static void gxf_write_packet_header(ByteIOContext *pb, pkt_type_t type)
+{
+    put_be32(pb, 0); /* packet leader for synchro */
+    put_byte(pb, 1);
+    put_byte(pb, type); /* map packet */
+    put_be32(pb, 0); /* size */
+    put_be32(pb, 0); /* reserved */
+    put_byte(pb, 0xE1); /* trailer 1 */
+    put_byte(pb, 0xE2); /* trailer 2 */
+}
+
+static int gxf_write_mpeg_auxiliary(ByteIOContext *pb, GXFStreamContext *ctx)
+{
+    char buffer[1024];
+    int size;
+
+    if (ctx->iframes) {
+        ctx->p_per_gop = ctx->pframes / ctx->iframes;
+        if (ctx->pframes % ctx->iframes)
+            ctx->p_per_gop++;
+        if (ctx->pframes)
+            ctx->b_per_gop = ctx->bframes / ctx->pframes;
+        if (ctx->p_per_gop > 9)
+            ctx->p_per_gop = 9; /* ensure value won't take more than one char */
+        if (ctx->b_per_gop > 9)
+            ctx->b_per_gop = 9; /* ensure value won't take more than one char */
+    }
+    size = snprintf(buffer, 1024, "Ver 1\nBr %.6f\nIpg 1\nPpi %d\nBpiop %d\n"
+                    "Pix 0\nCf %d\nCg 1\nSl 7\nnl16 %d\nVi 1\nf1 1\n",
+                    (float)ctx->codec->bit_rate, ctx->p_per_gop, ctx->b_per_gop,
+                    ctx->codec->pix_fmt == PIX_FMT_YUV422P ? 2 : 1,
+                    ctx->codec->height / 16);
+    put_byte(pb, 0x4F);
+    put_byte(pb, size + 1);
+    put_buffer(pb, (uint8_t *)buffer, size + 1);
+    return size + 3;
+}
+
+static int gxf_write_timecode_auxiliary(ByteIOContext *pb, GXFStreamContext *ctx)
+{
+    /* FIXME implement that */
+    put_byte(pb, 0); /* fields */
+    put_byte(pb, 0);  /* seconds */
+    put_byte(pb, 0); /* minutes */
+    put_byte(pb, 0); /* flags + hours */
+    /* reserved */
+    put_be32(pb, 0);
+    return 8;
+}
+
+static int gxf_write_track_description(ByteIOContext *pb, GXFStreamContext *stream)
+{
+    offset_t pos;
+
+    /* track description section */
+    put_byte(pb, stream->media_type + 0x80);
+    put_byte(pb, stream->index + 0xC0);
+
+    pos = url_ftell(pb);
+    put_be16(pb, 0); /* size */
+
+    /* media file name */
+    put_byte(pb, 0x4C);
+    put_byte(pb, strlen(ES_NAME_PATTERN) + 3);
+    put_tag(pb, ES_NAME_PATTERN);
+    put_be16(pb, stream->media_info);
+    put_byte(pb, 0);
+
+    if (stream->codec->codec_id != CODEC_ID_MPEG2VIDEO) {
+        /* auxiliary information */
+        put_byte(pb, 0x4D);
+        put_byte(pb, 8);
+        if (stream->codec->codec_id == CODEC_ID_NONE)
+            gxf_write_timecode_auxiliary(pb, stream);
+        else
+            put_le64(pb, 0);
+    }
+
+    /* file system version */
+    put_byte(pb, 0x4E);
+    put_byte(pb, 4);
+    put_be32(pb, 0);
+
+    if (stream->codec->codec_id == CODEC_ID_MPEG2VIDEO)
+        gxf_write_mpeg_auxiliary(pb, stream);
+
+    /* frame rate */
+    put_byte(pb, 0x50);
+    put_byte(pb, 4);
+    put_be32(pb, stream->frame_rate_index);
+
+    /* lines per frame */
+    put_byte(pb, 0x51);
+    put_byte(pb, 4);
+    put_be32(pb, stream->lines_index);
+
+    /* fields per frame */
+    put_byte(pb, 0x52);
+    put_byte(pb, 4);
+    put_be32(pb, stream->fields);
+
+    return updateSize(pb, pos);
+}
+
+static int gxf_write_material_data_section(ByteIOContext *pb, GXFContext *ctx)
+{
+    offset_t pos;
+    const char *filename = strrchr(ctx->fc->filename, '/');
+
+    pos = url_ftell(pb);
+    put_be16(pb, 0); /* size */
+
+    /* name */
+    if (filename)
+        filename++;
+    else
+        filename = ctx->fc->filename;
+    put_byte(pb, 0x40);
+    put_byte(pb, strlen(SERVER_PATH) + strlen(filename) + 1);
+    put_tag(pb, SERVER_PATH);
+    put_tag(pb, filename);
+    put_byte(pb, 0);
+
+    /* first field */
+    put_byte(pb, 0x41);
+    put_byte(pb, 4);
+    put_be32(pb, 0);
+
+    /* last field */
+    put_byte(pb, 0x42);
+    put_byte(pb, 4);
+    put_be32(pb, ctx->nb_frames);
+
+    /* reserved */
+    put_byte(pb, 0x43);
+    put_byte(pb, 4);
+    put_be32(pb, 0);
+
+    put_byte(pb, 0x44);
+    put_byte(pb, 4);
+    put_be32(pb, ctx->nb_frames);
+
+    /* estimated size */
+    put_byte(pb, 0x45);
+    put_byte(pb, 4);
+    put_be32(pb, url_fsize(pb) / 1024);
+
+    return updateSize(pb, pos);
+}
+
+static int gxf_write_track_description_section(ByteIOContext *pb, GXFContext *ctx)
+{
+    offset_t pos;
+    int i;
+
+    pos = url_ftell(pb);
+    put_be16(pb, 0); /* size */
+    for (i = 0; i < ctx->fc->nb_streams; ++i)
+        gxf_write_track_description(pb, &ctx->streams[i]);
+    return updateSize(pb, pos);
+}
+
+static int gxf_write_map_packet(ByteIOContext *pb, GXFContext *ctx)
+{
+    offset_t pos = url_ftell(pb);
+
+    gxf_write_packet_header(pb, PKT_MAP);
+
+    /* preamble */
+    put_byte(pb, 0xE0); /* version */
+    put_byte(pb, 0xFF); /* reserved */
+
+    gxf_write_material_data_section(pb, ctx);
+    gxf_write_track_description_section(pb, ctx);
+
+    return updatePacketSize(pb, pos);
+}
+
+#if 0
+static int gxf_write_flt_packet(ByteIOContext *pb, GXFContext *ctx)
+{
+    offset_t pos = url_ftell(pb);
+    int i;
+
+    gxf_write_packet_header(pb, PKT_FLT);
+
+    put_le32(pb, 1000); /* number of fields */
+    put_le32(pb, 0); /* number of active flt entries */
+
+    for (i = 0; i < 1000; ++i) {
+        put_le32(pb, 0);
+    }
+    return updatePacketSize(pb, pos);
+}
+#endif
+
+static int gxf_write_umf_material_description(ByteIOContext *pb, GXFContext *ctx)
+{
+    put_le32(pb, ctx->flags);
+    put_le32(pb, ctx->nb_frames); /* length of the longest track */
+    put_le32(pb, ctx->nb_frames); /* length of the shortest track */
+    put_le32(pb, 0); /* mark in */
+    put_le32(pb, ctx->nb_frames); /* mark out */
+    put_le32(pb, 0); /* timecode mark in */
+    put_le32(pb, ctx->nb_frames); /* timecode mark out */
+    put_le64(pb, ctx->fc->timestamp); /* modification time */
+    put_le64(pb, ctx->fc->timestamp); /* creation time */
+    put_le16(pb, 0); /* reserved */
+    put_le16(pb, 0); /* reserved */
+    put_le16(pb, ctx->audio_tracks);
+    put_le16(pb, 0); /* timecode track count */
+    put_le16(pb, 0); /* reserved */
+    put_le16(pb, ctx->mpeg_tracks);
+    return 48;
+}
+
+static int gxf_write_umf_payload(ByteIOContext *pb, GXFContext *ctx)
+{
+    put_le32(pb, ctx->umf_length); /* total length of the umf data */
+    put_le32(pb, 3); /* version */
+    put_le32(pb, ctx->fc->nb_streams);
+    put_le32(pb, ctx->umf_track_offset); /* umf track section offset */
+    put_le32(pb, ctx->umf_track_size);
+    put_le32(pb, ctx->fc->nb_streams);
+    put_le32(pb, ctx->umf_media_offset);
+    put_le32(pb, ctx->umf_media_size);
+    put_le32(pb, ctx->umf_user_data_offset); /* user data offset */
+    put_le32(pb, ctx->umf_user_data_size); /* user data size */
+    put_le32(pb, 0); /* reserved */
+    put_le32(pb, 0); /* reserved */
+    return 48;
+}
+
+static int gxf_write_umf_track_description(ByteIOContext *pb, GXFContext *ctx)
+{
+    offset_t pos = url_ftell(pb);
+    int tracks[255]={0};
+    int i;
+
+    ctx->umf_track_offset = pos - ctx->umf_start_offset;
+    for (i = 0; i < ctx->fc->nb_streams; ++i) {
+        AVStream *st = ctx->fc->streams[i];
+        GXFStreamContext *sc = &ctx->streams[i];
+        int id = 0;
+
+        switch (st->codec->codec_id) {
+        case CODEC_ID_MPEG1VIDEO: id= 'L'; break;
+        case CODEC_ID_MPEG2VIDEO: id= 'M'; break;
+        case CODEC_ID_PCM_S16LE:  id= 'A'; break;
+        case CODEC_ID_DVVIDEO:    id= sc->track_type == 6 ? 'E' : 'D'; break;
+        case CODEC_ID_MJPEG:      id= 'V'; break;
+        }
+        sc->media_info= id << 8;
+        /* FIXME first 10 audio tracks are 0 to 9 next 22 are A to V */
+        sc->media_info |= '0' + (tracks[id]++);
+        put_le16(pb, sc->media_info);
+        put_le16(pb, 1);
+    }
+    return url_ftell(pb) - pos;
+}
+
+static int gxf_write_umf_media_mpeg(ByteIOContext *pb, GXFStreamContext *stream)
+{
+    if (stream->codec->pix_fmt == PIX_FMT_YUV422P)
+        put_le32(pb, 2);
+    else
+        put_le32(pb, 1); /* default to 420 */
+    put_le32(pb, 1); /* closed = 1, open = 0, unknown = 255 */
+    put_le32(pb, 3); /* top = 1, bottom = 2, frame = 3, unknown = 0 */
+    put_le32(pb, 1); /* I picture per GOP */
+    put_le32(pb, stream->p_per_gop);
+    put_le32(pb, stream->b_per_gop);
+    if (stream->codec->codec_id == CODEC_ID_MPEG2VIDEO)
+        put_le32(pb, 2);
+    else if (stream->codec->codec_id == CODEC_ID_MPEG1VIDEO)
+        put_le32(pb, 1);
+    else
+        put_le32(pb, 0);
+    put_le32(pb, 0); /* reserved */
+    return 32;
+}
+
+static int gxf_write_umf_media_timecode(ByteIOContext *pb, GXFStreamContext *track)
+{
+    /* FIXME implement */
+    put_be32(pb, 0); /* drop frame flag */
+    put_be32(pb, 0); /* reserved */
+    put_be32(pb, 0); /* reserved */
+    put_be32(pb, 0); /* reserved */
+    put_be32(pb, 0); /* reserved */
+    put_be32(pb, 0); /* reserved */
+    put_be32(pb, 0); /* reserved */
+    put_be32(pb, 0); /* reserved */
+    return 32;
+}
+
+static int gxf_write_umf_media_dv(ByteIOContext *pb, GXFStreamContext *track)
+{
+    int i;
+
+    for (i = 0; i < 8; i++) {
+        put_be32(pb, 0);
+    }
+    return 32;
+}
+
+static int gxf_write_umf_media_audio(ByteIOContext *pb, GXFStreamContext *track)
+{
+    put_le64(pb, av_dbl2int(1)); /* sound level to begin to */
+    put_le64(pb, av_dbl2int(1)); /* sound level to begin to */
+    put_le32(pb, 0); /* number of fields over which to ramp up sound level */
+    put_le32(pb, 0); /* number of fields over which to ramp down sound level */
+    put_le32(pb, 0); /* reserved */
+    put_le32(pb, 0); /* reserved */
+    return 32;
+}
+
+#if 0
+static int gxf_write_umf_media_mjpeg(ByteIOContext *pb, GXFStreamContext *track)
+{
+    put_be64(pb, 0); /* FIXME FLOAT max chroma quant level */
+    put_be64(pb, 0); /* FIXME FLOAT max luma quant level */
+    put_be64(pb, 0); /* FIXME FLOAT min chroma quant level */
+    put_be64(pb, 0); /* FIXME FLOAT min luma quant level */
+    return 32;
+}
+#endif
+
+static int gxf_write_umf_media_description(ByteIOContext *pb, GXFContext *ctx)
+{
+    offset_t pos;
+    int i;
+
+    pos = url_ftell(pb);
+    ctx->umf_media_offset = pos - ctx->umf_start_offset;
+    for (i = 0; i < ctx->fc->nb_streams; ++i) {
+        GXFStreamContext *sc = &ctx->streams[i];
+        char buffer[88];
+        offset_t startpos, curpos;
+        int path_size = strlen(ES_NAME_PATTERN);
+
+        startpos = url_ftell(pb);
+        put_le16(pb, 0); /* length */
+        put_le16(pb, sc->media_info);
+        put_le16(pb, 0); /* reserved */
+        put_le16(pb, 0); /* reserved */
+        put_le32(pb, ctx->nb_frames);
+        put_le32(pb, 0); /* attributes rw, ro */
+        put_le32(pb, 0); /* mark in */
+        put_le32(pb, ctx->nb_frames); /* mark out */
+        strncpy(buffer, ES_NAME_PATTERN, path_size);
+        put_buffer(pb, (uint8_t *)buffer, path_size);
+        put_be16(pb, sc->media_info);
+        put_buffer(pb, (uint8_t *)buffer + path_size + 2, 88 - path_size - 2);
+        put_le32(pb, sc->track_type);
+        put_le32(pb, sc->sample_rate);
+        put_le32(pb, sc->sample_size);
+        put_le32(pb, 0); /* reserved */
+        switch (sc->codec->codec_id) {
+        case CODEC_ID_MPEG2VIDEO:
+            gxf_write_umf_media_mpeg(pb, sc);
+            break;
+        case CODEC_ID_PCM_S16LE:
+            gxf_write_umf_media_audio(pb, sc);
+            break;
+        case CODEC_ID_DVVIDEO:
+            gxf_write_umf_media_dv(pb, sc);
+            break;
+        default:
+            gxf_write_umf_media_timecode(pb, sc); /* 8 0bytes */
+        }
+        curpos = url_ftell(pb);
+        url_fseek(pb, startpos, SEEK_SET);
+        put_le16(pb, curpos - startpos);
+        url_fseek(pb, curpos, SEEK_SET);
+    }
+    return url_ftell(pb) - pos;
+}
+
+static int gxf_write_umf_user_data(ByteIOContext *pb, GXFContext *ctx)
+{
+    offset_t pos = url_ftell(pb);
+    ctx->umf_user_data_offset = pos - ctx->umf_start_offset;
+    put_le32(pb, 20);
+    put_le32(pb,  0);
+    put_le16(pb,  0);
+    put_le16(pb,  0);
+    put_le32(pb,  0);
+    put_byte(pb,  0);
+    put_byte(pb,  0);
+    put_byte(pb,  0);
+    put_byte(pb,  0);
+    return 20;
+}
+
+static int gxf_write_umf_packet(ByteIOContext *pb, GXFContext *ctx)
+{
+    offset_t pos = url_ftell(pb);
+
+    gxf_write_packet_header(pb, PKT_UMF);
+
+    /* preamble */
+    put_byte(pb, 3); /* first and last (only) packet */
+    put_be32(pb, ctx->umf_length); /* data length */
+
+    ctx->umf_start_offset = url_ftell(pb);
+    gxf_write_umf_payload(pb, ctx);
+    gxf_write_umf_material_description(pb, ctx);
+    ctx->umf_track_size = gxf_write_umf_track_description(pb, ctx);
+    ctx->umf_media_size = gxf_write_umf_media_description(pb, ctx);
+    ctx->umf_user_data_size = gxf_write_umf_user_data(pb, ctx);
+    ctx->umf_length = url_ftell(pb) - ctx->umf_start_offset;
+    return updatePacketSize(pb, pos);
+}
+
+static int gxf_write_header(AVFormatContext *s)
+{
+    ByteIOContext *pb = &s->pb;
+    GXFContext *gxf = s->priv_data;
+    int i;
+
+    gxf->fc = s;
+    gxf->flags |= 0x00080000; /* material is simple clip */
+    for (i = 0; i < s->nb_streams; ++i) {
+        AVStream *st = s->streams[i];
+        GXFStreamContext *sc = &gxf->streams[i];
+
+        sc->codec = st->codec;
+        sc->index = i;
+        sc->media_type = codec_get_tag(gxf_media_types, sc->codec->codec_id);
+        if (st->codec->codec_type == CODEC_TYPE_AUDIO) {
+            if (st->codec->codec_id != CODEC_ID_PCM_S16LE) {
+                av_log(s, AV_LOG_ERROR, "only 16 BIT PCM LE allowed for now\n");
+                return -1;
+            }
+            if (st->codec->sample_rate != 48000) {
+                av_log(s, AV_LOG_ERROR, "only 48000hz sampling rate is allowed\n");
+                return -1;
+            }
+            if (st->codec->channels != 1) {
+                av_log(s, AV_LOG_ERROR, "only mono tracks are allowed\n");
+                return -1;
+            }
+            sc->track_type = 2;
+            sc->sample_rate = st->codec->sample_rate;
+            sc->sample_size = 16;
+            sc->frame_rate_index = -2;
+            sc->lines_index = -2;
+            sc->fields = -2;
+            gxf->audio_tracks++;
+            gxf->flags |= 0x04000000; /* audio is 16 bit pcm */
+            fifo_init(&sc->audio_buffer, 3*GXF_AUDIO_PACKET_SIZE);
+        } else if (sc->codec->codec_type == CODEC_TYPE_VIDEO) {
+            /* FIXME check from time_base ? */
+            if (sc->codec->height == 480 || sc->codec->height == 512) { /* NTSC or NTSC+VBI */
+                sc->frame_rate_index = 5;
+                sc->sample_rate = 60;
+                gxf->flags |= 0x00000080;
+            } else { /* assume PAL */
+                sc->frame_rate_index = 6;
+                sc->media_type++;
+                sc->sample_rate = 50;
+                gxf->flags |= 0x00000040;
+            }
+            gxf->sample_rate = sc->sample_rate;
+            if (gxf_find_lines_index(sc) < 0)
+                sc->lines_index = -1;
+            sc->sample_size = st->codec->bit_rate;
+            sc->fields = 2; /* interlaced */
+            switch (sc->codec->codec_id) {
+            case CODEC_ID_MPEG2VIDEO:
+                sc->track_type = 4;
+                gxf->mpeg_tracks++;
+                gxf->flags |= 0x00008000;
+                break;
+            case CODEC_ID_DVVIDEO:
+                if (sc->codec->pix_fmt == PIX_FMT_YUV422P) {
+                    sc->media_type += 2;
+                    sc->track_type = 6;
+                    gxf->flags |= 0x00002000;
+                } else {
+                    sc->track_type = 5;
+                    gxf->flags |= 0x00001000;
+                }
+                break;
+            default:
+                av_log(NULL, AV_LOG_ERROR, "video codec not supported\n");
+                return -1;
+            }
+        }
+    }
+    gxf_write_map_packet(pb, gxf);
+    //gxf_write_flt_packet(pb, gxf);
+    gxf_write_umf_packet(pb, gxf);
+    put_flush_packet(pb);
+    return 0;
+}
+
+static int gxf_write_eos_packet(ByteIOContext *pb, GXFContext *ctx)
+{
+    offset_t pos = url_ftell(pb);
+
+    gxf_write_packet_header(pb, PKT_EOS);
+    return updatePacketSize(pb, pos);
+}
+
+static int gxf_write_trailer(AVFormatContext *s)
+{
+    ByteIOContext *pb = &s->pb;
+    GXFContext *gxf = s->priv_data;
+    offset_t end;
+    int i;
+
+    for (i = 0; i < s->nb_streams; ++i) {
+        if (s->streams[i]->codec->codec_type == CODEC_TYPE_AUDIO) {
+            fifo_free(&gxf->streams[i].audio_buffer);
+        }
+        if (s->streams[i]->codec->frame_number > gxf->nb_frames)
+            gxf->nb_frames = 2 * s->streams[i]->codec->frame_number;
+    }
+
+    gxf_write_eos_packet(pb, gxf);
+    end = url_ftell(pb);
+    url_fseek(pb, 0, SEEK_SET);
+    /* overwrite map and umf packets with new values */
+    gxf_write_map_packet(pb, gxf);
+    //gxf_write_flt_packet(pb, gxf);
+    gxf_write_umf_packet(pb, gxf);
+    url_fseek(pb, end, SEEK_SET);
+    return 0;
+}
+
+static int gxf_write_media_preamble(ByteIOContext *pb, GXFContext *ctx, AVPacket *pkt, int size)
+{
+    GXFStreamContext *sc = &ctx->streams[pkt->stream_index];
+
+    put_byte(pb, sc->media_type);
+    put_byte(pb, sc->index);
+    put_be32(pb, ctx->field_number);
+    if (sc->codec->codec_type == CODEC_TYPE_AUDIO) {
+        put_be16(pb, 0);
+        put_be16(pb, size / 2);
+    } else if (sc->codec->codec_id == CODEC_ID_MPEG2VIDEO) {
+        if (pkt->flags & PKT_FLAG_KEY) {
+            put_byte(pb, 0x0d);
+            sc->iframes++;
+        } else if (pkt->pts != pkt->dts) {
+            put_byte(pb, 0x0f);
+            sc->bframes++;
+        } else {
+            put_byte(pb, 0x0e);
+            sc->pframes++;
+        }
+        put_be24(pb, size);
+    } else if (sc->codec->codec_id == CODEC_ID_DVVIDEO) {
+        put_byte(pb, size / 4096);
+        put_be24(pb, 0);
+    } else
+        put_be32(pb, size);
+    put_be32(pb, ctx->field_number);
+    put_byte(pb, 1); /* flags */
+    put_byte(pb, 0); /* reserved */
+    return 16;
+}
+
+static int gxf_write_media_packet(ByteIOContext *pb, GXFContext *ctx, AVPacket *pkt)
+{
+    GXFStreamContext *sc = &ctx->streams[pkt->stream_index];
+    offset_t pos = url_ftell(pb);
+    int padding = 0;
+
+    gxf_write_packet_header(pb, PKT_MEDIA);
+    if (sc->codec->codec_id == CODEC_ID_MPEG2VIDEO && pkt->size % 4) /* MPEG-2 frames must be padded */
+        padding = 4 - pkt->size % 4;
+    gxf_write_media_preamble(pb, ctx, pkt, pkt->size + padding);
+    if (sc->codec->codec_type == CODEC_TYPE_AUDIO)
+        put_buffer(pb, pkt->data, GXF_AUDIO_PACKET_SIZE);
+    else {
+        ctx->field_number += 2;
+        put_buffer(pb, pkt->data, pkt->size);
+    }
+    gxf_write_padding(pb, padding);
+    return updatePacketSize(pb, pos);
+}
+
+static int gxf_write_packet(AVFormatContext *s, AVPacket *pkt)
+{
+    GXFContext *gxf = s->priv_data;
+
+    gxf_write_media_packet(&s->pb, gxf, pkt);
+    put_flush_packet(&s->pb);
+    return 0;
+}
+
+static int gxf_interleave_packet(AVFormatContext *s, AVPacket *out, AVPacket *pkt, int flush)
+{
+    AVPacketList *pktl, **next_point, *this_pktl;
+    GXFContext *gxf = s->priv_data;
+    GXFStreamContext *sc;
+    int i;
+
+    if (pkt) {
+        sc = &gxf->streams[pkt->stream_index];
+        if (sc->codec->codec_type == CODEC_TYPE_AUDIO) {
+            fifo_write(&sc->audio_buffer, pkt->data, pkt->size, NULL);
+        } else {
+            this_pktl = av_mallocz(sizeof(AVPacketList));
+            this_pktl->pkt = *pkt;
+            if(pkt->destruct == av_destruct_packet)
+                pkt->destruct = NULL; // non shared -> must keep original from being freed
+            else
+                av_dup_packet(&this_pktl->pkt); //shared -> must dup
+            next_point = &s->packet_buffer;
+            while(*next_point){
+                AVStream *st= s->streams[ pkt->stream_index];
+                AVStream *st2= s->streams[ (*next_point)->pkt.stream_index];
+                int64_t left=  st2->time_base.num * (int64_t)st ->time_base.den;
+                int64_t right= st ->time_base.num * (int64_t)st2->time_base.den;
+                if((*next_point)->pkt.dts * left > pkt->dts * right) //FIXME this can overflow
+                    break;
+                next_point= &(*next_point)->next;
+            }
+            this_pktl->next = *next_point;
+            *next_point = this_pktl;
+        }
+    }
+
+    if (gxf->audio_written == gxf->audio_tracks) {
+        if (!s->packet_buffer) {
+            gxf->audio_written = 0;
+            return 0;
+        }
+        pktl = s->packet_buffer;
+        *out = pktl->pkt;
+        s->packet_buffer = pktl->next;
+        av_freep(&pktl);
+        return 1;
+    } else {
+        for (i = 0; i < s->nb_streams; i++) {
+            sc = &gxf->streams[i];
+            if (sc->codec->codec_type == CODEC_TYPE_AUDIO &&
+                (flush || fifo_size(&sc->audio_buffer, NULL) >= GXF_AUDIO_PACKET_SIZE)) {
+                int size = flush ? fifo_size(&sc->audio_buffer, NULL) : GXF_AUDIO_PACKET_SIZE;
+                av_new_packet(out, GXF_AUDIO_PACKET_SIZE);
+                fifo_read(&sc->audio_buffer, out->data, size, NULL);
+                gxf->audio_written++;
+                out->stream_index = i;
+                out->size = size;
+                return 1;
+            }
+        }
+    }
+    av_init_packet(out);
+    return 0;
+}
+
+AVOutputFormat gxf_muxer = {
+    "gxf",
+    "GXF format",
+    NULL,
+    "gxf",
+    sizeof(GXFContext),
+    CODEC_ID_PCM_S16LE,
+    CODEC_ID_MPEG2VIDEO,
+    gxf_write_header,
+    gxf_write_packet,
+    gxf_write_trailer,
+    0,
+    NULL,
+    gxf_interleave_packet,
+};