diff --git a/configure b/configure
index 8443db4370..ba83376474 100755
--- a/configure
+++ b/configure
@@ -3917,7 +3917,9 @@ for func in $MATH_FUNCS; do
 done
 
 # these are off by default, so fail if requested and not available
-enabled avisynth   && require2 vfw32 "windows.h vfw.h" AVIFileInit -lavifil32
+enabled avisynth   && { { check_lib2 "windows.h" LoadLibrary; } ||
+                        { check_lib2 "dlfcn.h" dlopen -ldl; } ||
+                        die "ERROR: LoadLibrary/dlopen not found for avisynth"; }
 enabled fontconfig && require_pkg_config fontconfig "fontconfig/fontconfig.h" FcInit
 enabled frei0r     && { check_header frei0r.h || die "ERROR: frei0r.h header not found"; }
 enabled gnutls     && require_pkg_config gnutls gnutls/gnutls.h gnutls_global_init
diff --git a/libavformat/avisynth.c b/libavformat/avisynth.c
index 1e4dee1b00..d31031dd15 100644
--- a/libavformat/avisynth.c
+++ b/libavformat/avisynth.c
@@ -1,9 +1,8 @@
 /*
- * AVISynth support
- * Copyright (c) 2006 DivX, Inc.
- *
- * This file is part of FFmpeg.
+ * Avi/AvxSynth support
+ * Copyright (c) 2012 AvxSynth Team.
  *
+ * 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
@@ -21,214 +20,619 @@
 
 #include "avformat.h"
 #include "internal.h"
-#include "riff.h"
+#include "libavcodec/internal.h"
 
-#include <windows.h>
-#include <vfw.h>
+// Enable function pointer definitions for runtime loading.
+#define AVSC_NO_DECLSPEC
 
-typedef struct {
-  PAVISTREAM handle;
-  AVISTREAMINFO info;
-  DWORD read;
-  LONG chunck_size;
-  LONG chunck_samples;
-} AVISynthStream;
+// Shut up ffmpeg error messages.
+// avisynth_c.h contains inline functions that call these functions.
+#undef malloc
+#undef free
+#undef printf
 
-typedef struct {
-  PAVIFILE file;
-  AVISynthStream *streams;
-  int nb_streams;
-  int next_stream;
-} AVISynthContext;
+// Platform-specific directives for AviSynth vs AvxSynth.
+#ifdef _WIN32
+  #include <windows.h>
+  #undef EXTERN_C
+  #include "compat/avisynth/avisynth_c.h"
+  #define AVISYNTH_LIB "avisynth"
+#else
+  #include <dlfcn.h>
+  #include "compat/avisynth/avxsynth_c.h"
+   #if defined (__APPLE__)
+     #define AVISYNTH_LIB "libavxsynth.dylib"
+   #else
+     #define AVISYNTH_LIB "libavxsynth.so"
+   #endif
 
-static int avisynth_read_header(AVFormatContext *s)
-{
-  AVISynthContext *avs = s->priv_data;
-  HRESULT res;
-  AVIFILEINFO info;
-  DWORD id;
-  AVStream *st;
-  AVISynthStream *stream;
-  wchar_t filename_wchar[1024] = { 0 };
-  char filename_char[1024] = { 0 };
-
-  AVIFileInit();
-
-  /* avisynth can't accept UTF-8 filename */
-  MultiByteToWideChar(CP_UTF8, 0, s->filename, -1, filename_wchar, 1024);
-  WideCharToMultiByte(CP_THREAD_ACP, 0, filename_wchar, -1, filename_char, 1024, NULL, NULL);
-  res = AVIFileOpen(&avs->file, filename_char, OF_READ|OF_SHARE_DENY_WRITE, NULL);
-  if (res != S_OK)
-    {
-      av_log(s, AV_LOG_ERROR, "AVIFileOpen failed with error %ld\n", res);
-      AVIFileExit();
-      return -1;
-    }
-
-  res = AVIFileInfo(avs->file, &info, sizeof(info));
-  if (res != S_OK)
-    {
-      av_log(s, AV_LOG_ERROR, "AVIFileInfo failed with error %ld\n", res);
-      AVIFileExit();
-      return -1;
-    }
-
-  avs->streams = av_mallocz(info.dwStreams * sizeof(AVISynthStream));
-
-  for (id=0; id<info.dwStreams; id++)
-    {
-      stream = &avs->streams[id];
-      stream->read = 0;
-      if (AVIFileGetStream(avs->file, &stream->handle, 0, id) == S_OK)
-        {
-          if (AVIStreamInfo(stream->handle, &stream->info, sizeof(stream->info)) == S_OK)
-            {
-              if (stream->info.fccType == streamtypeAUDIO)
-                {
-                  WAVEFORMATEX wvfmt;
-                  LONG struct_size = sizeof(WAVEFORMATEX);
-                  if (AVIStreamReadFormat(stream->handle, 0, &wvfmt, &struct_size) != S_OK)
-                    continue;
-
-                  st = avformat_new_stream(s, NULL);
-                  st->id = id;
-                  st->codec->codec_type = AVMEDIA_TYPE_AUDIO;
-
-                  st->codec->block_align = wvfmt.nBlockAlign;
-                  st->codec->channels = wvfmt.nChannels;
-                  st->codec->sample_rate = wvfmt.nSamplesPerSec;
-                  st->codec->bit_rate = wvfmt.nAvgBytesPerSec * 8;
-                  st->codec->bits_per_coded_sample = wvfmt.wBitsPerSample;
-
-                  stream->chunck_samples = wvfmt.nSamplesPerSec * (uint64_t)info.dwScale / (uint64_t)info.dwRate;
-                  stream->chunck_size = stream->chunck_samples * wvfmt.nChannels * wvfmt.wBitsPerSample / 8;
-
-                  st->codec->codec_tag = wvfmt.wFormatTag;
-                  st->codec->codec_id = ff_wav_codec_get_id(wvfmt.wFormatTag, st->codec->bits_per_coded_sample);
-                }
-              else if (stream->info.fccType == streamtypeVIDEO)
-                {
-                  BITMAPINFO imgfmt;
-                  LONG struct_size = sizeof(BITMAPINFO);
-
-                  stream->chunck_size = stream->info.dwSampleSize;
-                  stream->chunck_samples = 1;
-
-                  if (AVIStreamReadFormat(stream->handle, 0, &imgfmt, &struct_size) != S_OK)
-                    continue;
-
-                  st = avformat_new_stream(s, NULL);
-                  st->id = id;
-                  st->codec->codec_type = AVMEDIA_TYPE_VIDEO;
-                  st->avg_frame_rate.num = stream->info.dwRate;
-                  st->avg_frame_rate.den = stream->info.dwScale;
-#if FF_API_R_FRAME_RATE
-                  st->r_frame_rate = st->avg_frame_rate;
+  #define LoadLibrary(x) dlopen(x, RTLD_NOW | RTLD_GLOBAL)
+  #define GetProcAddress dlsym
+  #define FreeLibrary dlclose
 #endif
 
-                  st->codec->width = imgfmt.bmiHeader.biWidth;
-                  st->codec->height = imgfmt.bmiHeader.biHeight;
+// AvxSynth doesn't have these colorspaces, so disable them
+#ifndef _WIN32
+#define avs_is_yv24(vi) 0
+#define avs_is_yv16(vi) 0
+#define avs_is_yv411(vi) 0
+#define avs_is_y8(vi) 0
+#endif
 
-                  st->codec->bits_per_coded_sample = imgfmt.bmiHeader.biBitCount;
-                  st->codec->bit_rate = (uint64_t)stream->info.dwSampleSize * (uint64_t)stream->info.dwRate * 8 / (uint64_t)stream->info.dwScale;
-                  st->codec->codec_tag = imgfmt.bmiHeader.biCompression;
-                  st->codec->codec_id = ff_codec_get_id(ff_codec_bmp_tags, imgfmt.bmiHeader.biCompression);
-                  if (st->codec->codec_id == AV_CODEC_ID_RAWVIDEO && imgfmt.bmiHeader.biCompression== BI_RGB) {
-                    st->codec->extradata = av_malloc(9 + FF_INPUT_BUFFER_PADDING_SIZE);
-                    if (st->codec->extradata) {
-                      st->codec->extradata_size = 9;
-                      memcpy(st->codec->extradata, "BottomUp", 9);
-                    }
-                  }
+typedef struct {
+    void *library;
+#define AVSC_DECLARE_FUNC(name) name##_func name
+    AVSC_DECLARE_FUNC(avs_create_script_environment);
+    AVSC_DECLARE_FUNC(avs_delete_script_environment);
+    AVSC_DECLARE_FUNC(avs_get_error);
+    AVSC_DECLARE_FUNC(avs_clip_get_error);
+    AVSC_DECLARE_FUNC(avs_invoke);
+    AVSC_DECLARE_FUNC(avs_release_value);
+    AVSC_DECLARE_FUNC(avs_get_video_info);
+    AVSC_DECLARE_FUNC(avs_take_clip);
+    AVSC_DECLARE_FUNC(avs_release_clip);
+    AVSC_DECLARE_FUNC(avs_bit_blt);
+    AVSC_DECLARE_FUNC(avs_get_audio);
+    AVSC_DECLARE_FUNC(avs_get_frame);
+    AVSC_DECLARE_FUNC(avs_release_video_frame);
+#undef AVSC_DECLARE_FUNC
+} AviSynthLibrary;
 
+struct AviSynthContext {
+    AVS_ScriptEnvironment *env;
+    AVS_Clip *clip;
+    const AVS_VideoInfo *vi;
 
-                  st->duration = stream->info.dwLength;
-                }
-              else
-                {
-                  AVIStreamRelease(stream->handle);
-                  continue;
-                }
+    // avisynth_read_packet_video() iterates over this.
+    int n_planes;
+    const int *planes;
 
-              avs->nb_streams++;
+    int curr_stream;
+    int curr_frame;
+    int64_t curr_sample;
 
-              st->codec->stream_codec_tag = stream->info.fccHandler;
+    int error;
 
-              avpriv_set_pts_info(st, 64, info.dwScale, info.dwRate);
-              st->start_time = stream->info.dwStart;
-            }
+    // Linked list pointers.
+    struct AviSynthContext *next;
+};
+typedef struct AviSynthContext AviSynthContext;
+
+static const int avs_planes_packed[1] = {0};
+static const int avs_planes_grey[1] = {AVS_PLANAR_Y};
+static const int avs_planes_yuv[3] = {AVS_PLANAR_Y, AVS_PLANAR_U, AVS_PLANAR_V};
+
+// A conflict between C++ global objects, atexit, and dynamic loading requires
+// us to register our own atexit handler to prevent double freeing.
+static AviSynthLibrary *avs_library = NULL;
+static int avs_atexit_called = 0;
+
+// Linked list of AviSynthContexts. An atexit handler destroys this list.
+static AviSynthContext *avs_ctx_list = NULL;
+
+static av_cold void avisynth_atexit_handler(void);
+
+static av_cold int avisynth_load_library(void) {
+    avs_library = av_mallocz(sizeof(AviSynthLibrary));
+    if (!avs_library)
+        return AVERROR_UNKNOWN;
+
+    avs_library->library = LoadLibrary(AVISYNTH_LIB);
+    if (!avs_library->library)
+        goto init_fail;
+
+#define LOAD_AVS_FUNC(name, continue_on_fail) \
+{ \
+    avs_library->name = (void*)GetProcAddress(avs_library->library, #name); \
+    if(!continue_on_fail && !avs_library->name) \
+        goto fail; \
+}
+    LOAD_AVS_FUNC(avs_create_script_environment, 0);
+    LOAD_AVS_FUNC(avs_delete_script_environment, 0);
+    LOAD_AVS_FUNC(avs_get_error, 1); // New to AviSynth 2.6
+    LOAD_AVS_FUNC(avs_clip_get_error, 0);
+    LOAD_AVS_FUNC(avs_invoke, 0);
+    LOAD_AVS_FUNC(avs_release_value, 0);
+    LOAD_AVS_FUNC(avs_get_video_info, 0);
+    LOAD_AVS_FUNC(avs_take_clip, 0);
+    LOAD_AVS_FUNC(avs_release_clip, 0);
+    LOAD_AVS_FUNC(avs_bit_blt, 0);
+    LOAD_AVS_FUNC(avs_get_audio, 0);
+    LOAD_AVS_FUNC(avs_get_frame, 0);
+    LOAD_AVS_FUNC(avs_release_video_frame, 0);
+#undef LOAD_AVS_FUNC
+
+    atexit(avisynth_atexit_handler);
+    return 0;
+
+fail:
+    FreeLibrary(avs_library->library);
+init_fail:
+    av_freep(&avs_library);
+    return AVERROR_UNKNOWN;
+}
+
+// Note that avisynth_context_create and avisynth_context_destroy
+// do not allocate or free the actual context! That is taken care of
+// by libavformat.
+static av_cold int avisynth_context_create(AVFormatContext *s) {
+    AviSynthContext *avs = (AviSynthContext *)s->priv_data;
+    int ret;
+
+    if (!avs_library) {
+        if (ret = avisynth_load_library())
+            return ret;
+    }
+
+    if (!avs)
+        return AVERROR_UNKNOWN;
+
+    if (!avs_ctx_list) {
+        avs_ctx_list = avs;
+    } else {
+        avs->next = avs_ctx_list;
+        avs_ctx_list = avs;
+    }
+
+    avs->env = avs_library->avs_create_script_environment(3);
+    if (avs_library->avs_get_error) {
+        const char *error = avs_library->avs_get_error(avs->env);
+        if (error) {
+            av_log(s, AV_LOG_ERROR, "%s\n", error);
+            av_free(avs);
+            return AVERROR_UNKNOWN;
         }
     }
 
-  return 0;
+    return 0;
 }
 
-static int avisynth_read_packet(AVFormatContext *s, AVPacket *pkt)
-{
-  AVISynthContext *avs = s->priv_data;
-  HRESULT res;
-  AVISynthStream *stream;
-  int stream_id = avs->next_stream;
-  LONG read_size;
+static av_cold void avisynth_context_destroy(AviSynthContext *avs) {
+    if (avs_atexit_called)
+       return;
 
-  // handle interleaving manually...
-  stream = &avs->streams[stream_id];
-
-  if (stream->read >= stream->info.dwLength)
-    return AVERROR(EIO);
-
-  if (av_new_packet(pkt, stream->chunck_size))
-    return AVERROR(EIO);
-  pkt->stream_index = stream_id;
-  pkt->pts = avs->streams[stream_id].read / avs->streams[stream_id].chunck_samples;
-
-  res = AVIStreamRead(stream->handle, stream->read, stream->chunck_samples, pkt->data, stream->chunck_size, &read_size, NULL);
-
-  pkt->size = read_size;
-
-  stream->read += stream->chunck_samples;
-
-  // prepare for the next stream to read
-  do {
-    avs->next_stream = (avs->next_stream+1) % avs->nb_streams;
-  } while (avs->next_stream != stream_id && s->streams[avs->next_stream]->discard >= AVDISCARD_ALL);
-
-  return (res == S_OK) ? pkt->size : -1;
-}
-
-static int avisynth_read_close(AVFormatContext *s)
-{
-  AVISynthContext *avs = s->priv_data;
-  int i;
-
-  for (i=0;i<avs->nb_streams;i++)
-    {
-      AVIStreamRelease(avs->streams[i].handle);
+    if (avs == avs_ctx_list) {
+        avs_ctx_list = avs->next;
+    } else {
+        AviSynthContext *prev = avs_ctx_list;
+        while (prev->next != avs)
+            prev = prev->next;
+        prev->next = avs->next;
     }
 
-  av_free(avs->streams);
-  AVIFileRelease(avs->file);
-  AVIFileExit();
-  return 0;
+    if (avs->clip) {
+        avs_library->avs_release_clip(avs->clip);
+        avs->clip = NULL;
+    }
+    if (avs->env) {
+        avs_library->avs_delete_script_environment(avs->env);
+        avs->env = NULL;
+    }
 }
 
-static int avisynth_read_seek(AVFormatContext *s, int stream_index, int64_t pts, int flags)
-{
-  AVISynthContext *avs = s->priv_data;
-  int stream_id;
+static av_cold void avisynth_atexit_handler(void) {
+    AviSynthContext *avs = avs_ctx_list;
 
-  for (stream_id = 0; stream_id < avs->nb_streams; stream_id++)
-    {
-      avs->streams[stream_id].read = pts * avs->streams[stream_id].chunck_samples;
+    while (avs) {
+        AviSynthContext *next = avs->next;
+        avisynth_context_destroy(avs);
+        avs = next;
+    }
+    FreeLibrary(avs_library->library);
+    av_freep(&avs_library);
+
+    avs_atexit_called = 1;
+}
+
+// Create AVStream from audio and video data.
+static int avisynth_create_stream_video(AVFormatContext *s, AVStream *st) {
+    AviSynthContext *avs = s->priv_data;
+    int planar = 0; // 0: packed, 1: YUV, 2: Y8
+
+    st->codec->codec_type = AVMEDIA_TYPE_VIDEO;
+    st->codec->codec_id = CODEC_ID_RAWVIDEO;
+    st->codec->width = avs->vi->width;
+    st->codec->height = avs->vi->height;
+
+    st->time_base = (AVRational) {avs->vi->fps_denominator, avs->vi->fps_numerator};
+    st->avg_frame_rate = (AVRational) {avs->vi->fps_numerator, avs->vi->fps_denominator};
+    st->start_time = 0;
+    st->duration = avs->vi->num_frames;
+    st->nb_frames = avs->vi->num_frames;
+
+    switch (avs->vi->pixel_type) {
+#ifdef _WIN32
+    case AVS_CS_YV24:
+        st->codec->pix_fmt = PIX_FMT_YUV444P;
+        planar = 1;
+        break;
+    case AVS_CS_YV16:
+        st->codec->pix_fmt = PIX_FMT_YUV422P;
+        planar = 1;
+        break;
+    case AVS_CS_YV411:
+        st->codec->pix_fmt = PIX_FMT_YUV411P;
+        planar = 1;
+        break;
+    case AVS_CS_Y8:
+        st->codec->pix_fmt = PIX_FMT_GRAY8;
+        planar = 2;
+        break;
+#endif
+    case AVS_CS_BGR24:
+        st->codec->pix_fmt = PIX_FMT_RGB24;
+        break;
+    case AVS_CS_BGR32:
+        st->codec->pix_fmt = PIX_FMT_RGB32;
+        break;
+    case AVS_CS_YUY2:
+        st->codec->pix_fmt = PIX_FMT_YUYV422;
+        break;
+    case AVS_CS_YV12:
+        st->codec->pix_fmt = PIX_FMT_YUV420P;
+        planar = 1;
+        break;
+    case AVS_CS_I420: // Is this even used anywhere?
+        st->codec->pix_fmt = PIX_FMT_YUV420P;
+        planar = 1;
+        break;
+    default:
+        av_log(s, AV_LOG_ERROR, "unknown AviSynth colorspace %d\n", avs->vi->pixel_type);
+        avs->error = 1;
+        return AVERROR_UNKNOWN;
     }
 
-  return 0;
+    switch (planar) {
+    case 2: // Y8
+        avs->n_planes = 1;
+        avs->planes = avs_planes_grey;
+        break;
+    case 1: // YUV
+        avs->n_planes = 3;
+        avs->planes = avs_planes_yuv;
+        break;
+    default:
+        avs->n_planes = 1;
+        avs->planes = avs_planes_packed;
+    }
+    return 0;
+}
+
+static int avisynth_create_stream_audio(AVFormatContext *s, AVStream *st) {
+    AviSynthContext *avs = s->priv_data;
+
+    st->codec->codec_type = AVMEDIA_TYPE_AUDIO;
+    st->codec->sample_rate = avs->vi->audio_samples_per_second;
+    st->codec->channels = avs->vi->nchannels;
+    st->time_base = (AVRational) {1, avs->vi->audio_samples_per_second};
+
+    switch (avs->vi->sample_type) {
+    case AVS_SAMPLE_INT8:
+        st->codec->codec_id = CODEC_ID_PCM_U8;
+        break;
+    case AVS_SAMPLE_INT16:
+        st->codec->codec_id = CODEC_ID_PCM_S16LE;
+        break;
+    case AVS_SAMPLE_INT24:
+        st->codec->codec_id = CODEC_ID_PCM_S24LE;
+        break;
+    case AVS_SAMPLE_INT32:
+        st->codec->codec_id = CODEC_ID_PCM_S32LE;
+        break;
+    case AVS_SAMPLE_FLOAT:
+        st->codec->codec_id = CODEC_ID_PCM_F32LE;
+        break;
+    default:
+        av_log(s, AV_LOG_ERROR, "unknown AviSynth sample type %d\n", avs->vi->sample_type);
+        avs->error = 1;
+        return AVERROR_UNKNOWN;
+    }
+    return 0;
+}
+
+static int avisynth_create_stream(AVFormatContext *s) {
+    AviSynthContext *avs = s->priv_data;
+    AVStream *st;
+    int ret;
+    int id = 0;
+
+    if (avs_has_video(avs->vi)) {
+        st = avformat_new_stream(s, NULL);
+        if (!st)
+            return AVERROR_UNKNOWN;
+        st->id = id++;
+        if (ret = avisynth_create_stream_video(s, st))
+            return ret;
+    }
+    if (avs_has_audio(avs->vi)) {
+        st = avformat_new_stream(s, NULL);
+        if (!st)
+            return AVERROR_UNKNOWN;
+        st->id = id++;
+        if (ret = avisynth_create_stream_audio(s, st))
+            return ret;
+    }
+    return 0;
+}
+
+static int avisynth_open_file(AVFormatContext *s) {
+    AviSynthContext *avs = (AviSynthContext *)s->priv_data;
+    AVS_Value arg, val;
+    int ret;
+
+    if (ret = avisynth_context_create(s))
+        return ret;
+
+    arg = avs_new_value_string(s->filename);
+    val = avs_library->avs_invoke(avs->env, "Import", arg, 0);
+    if (avs_is_error(val)) {
+        av_log(s, AV_LOG_ERROR, "%s\n", avs_as_error(val));
+        ret = AVERROR_UNKNOWN;
+        goto fail;
+    }
+    if (!avs_is_clip(val)) {
+        av_log(s, AV_LOG_ERROR, "%s\n", "AviSynth script did not return a clip");
+        ret = AVERROR_UNKNOWN;
+        goto fail;
+    }
+
+    avs->clip = avs_library->avs_take_clip(val, avs->env);
+    avs->vi = avs_library->avs_get_video_info(avs->clip);
+
+    // Release the AVS_Value as it will go out of scope.
+    avs_library->avs_release_value(val);
+
+    if (ret = avisynth_create_stream(s))
+        goto fail;
+
+    return 0;
+
+fail:
+    avisynth_context_destroy(avs);
+    return ret;
+}
+
+static void avisynth_next_stream(AVFormatContext *s, AVStream **st, AVPacket *pkt, int *discard) {
+    AviSynthContext *avs = s->priv_data;
+
+    pkt->stream_index = avs->curr_stream++;
+    avs->curr_stream %= s->nb_streams;
+
+    *st = s->streams[pkt->stream_index];
+    if ((*st)->discard == AVDISCARD_ALL)
+        *discard = 1;
+    else
+        *discard = 0;
+
+    return;
+}
+
+// Copy AviSynth clip data into an AVPacket.
+static int avisynth_read_packet_video(AVFormatContext *s, AVPacket *pkt, int discard) {
+    AviSynthContext *avs = s->priv_data;
+    AVS_VideoFrame *frame;
+    unsigned char*  dst_p;
+    const unsigned char* src_p;
+    int i, plane, rowsize, planeheight, pitch, bits;
+    const char* error;
+
+    if (avs->curr_frame >= avs->vi->num_frames)
+        return AVERROR_EOF;
+
+    // This must happen even if the stream is discarded to prevent desync.
+    avs->curr_frame++;
+    if (discard)
+        return 0;
+
+    pkt->pts = avs->curr_frame;
+    pkt->dts = avs->curr_frame;
+    pkt->duration = 1;
+
+    // Define the bpp values for the new AviSynth 2.6 colorspaces
+    if (avs_is_yv24(avs->vi)) {
+        bits = 24;
+    } else if (avs_is_yv16(avs->vi)) {
+        bits = 16;
+    } else if (avs_is_yv411(avs->vi)) {
+        bits = 12;
+    } else if (avs_is_y8(avs->vi)) {
+        bits = 8;
+    } else {
+        bits = avs_bits_per_pixel(avs->vi);
+    }
+
+    // Without cast to int64_t, calculation overflows at about 9k x 9k resolution.
+    pkt->size = (((int64_t)avs->vi->width * (int64_t)avs->vi->height) * bits) / 8;
+    if (!pkt->size)
+        return AVERROR_UNKNOWN;
+    pkt->data = av_malloc(pkt->size);
+    if (!pkt->data)
+        return AVERROR_UNKNOWN;
+
+    frame = avs_library->avs_get_frame(avs->clip, avs->curr_frame);
+    error = avs_library->avs_clip_get_error(avs->clip);
+    if (error) {
+        av_log(s, AV_LOG_ERROR, "%s\n", error);
+        avs->error = 1;
+        av_freep(&pkt->data);
+        return AVERROR_UNKNOWN;
+    }
+
+    dst_p = pkt->data;
+    for (i = 0; i < avs->n_planes; i++) {
+        plane = avs->planes[i];
+        src_p = avs_get_read_ptr_p(frame, plane);
+        rowsize = avs_get_row_size_p(frame, plane);
+        planeheight = avs_get_height_p(frame, plane);
+        pitch = avs_get_pitch_p(frame, plane);
+
+        // Flip RGB video.
+        if (avs_is_rgb24(avs->vi) || avs_is_rgb(avs->vi)) {
+            src_p = src_p + (planeheight - 1) * pitch;
+            pitch = -pitch;
+        }
+
+        avs_library->avs_bit_blt(avs->env, dst_p, rowsize, src_p, pitch, rowsize, planeheight);
+        dst_p += rowsize * planeheight;
+    }
+
+    avs_library->avs_release_video_frame(frame);
+    return 0;
+}
+
+static int avisynth_read_packet_audio(AVFormatContext *s, AVPacket *pkt, int discard) {
+    AviSynthContext *avs = s->priv_data;
+    AVRational fps, samplerate;
+    int samples;
+    const char* error;
+
+    if (avs->curr_sample >= avs->vi->num_audio_samples)
+        return AVERROR_EOF;
+
+    fps.num = avs->vi->fps_numerator;
+    fps.den = avs->vi->fps_denominator;
+    samplerate.num = avs->vi->audio_samples_per_second;
+    samplerate.den = 1;
+
+    if (avs_has_video(avs->vi)) {
+        if (avs->curr_frame < avs->vi->num_frames)
+            samples = av_rescale_q(avs->curr_frame, samplerate, fps) - avs->curr_sample;
+        else
+            samples = av_rescale_q(1, samplerate, fps);
+    } else {
+        samples = 1000;
+    }
+
+    // After seeking, audio may catch up with video.
+    if (samples <= 0) {
+        pkt->size = 0;
+        pkt->data = NULL;
+        return 0;
+    }
+
+    if (avs->curr_sample + samples > avs->vi->num_audio_samples)
+        samples = avs->vi->num_audio_samples - avs->curr_sample;
+
+    // This must happen even if the stream is discarded to prevent desync.
+    avs->curr_sample += samples;
+    if (discard)
+        return 0;
+
+    pkt->pts = avs->curr_sample;
+    pkt->dts = avs->curr_sample;
+    pkt->duration = samples;
+
+    pkt->size = avs_bytes_per_channel_sample(avs->vi) * samples * avs->vi->nchannels;
+    if (!pkt->size)
+        return AVERROR_UNKNOWN;
+    pkt->data = av_malloc(pkt->size);
+    if (!pkt->data)
+        return AVERROR_UNKNOWN;
+
+    avs_library->avs_get_audio(avs->clip, pkt->data, avs->curr_sample, samples);
+    error = avs_library->avs_clip_get_error(avs->clip);
+    if (error) {
+        av_log(s, AV_LOG_ERROR, "%s\n", error);
+        avs->error = 1;
+        av_freep(&pkt->data);
+        return AVERROR_UNKNOWN;
+    }
+    return 0;
+}
+
+static av_cold int avisynth_read_header(AVFormatContext *s) {
+    int ret;
+
+    // Calling library must implement a lock for thread-safe opens.
+    if (ret = avpriv_lock_avformat())
+        return ret;
+
+    if (ret = avisynth_open_file(s)) {
+        avpriv_unlock_avformat();
+        return ret;
+    }
+
+    avpriv_unlock_avformat();
+    return 0;
+}
+
+static int avisynth_read_packet(AVFormatContext *s, AVPacket *pkt) {
+    AviSynthContext *avs = s->priv_data;
+    AVStream *st;
+    int discard = 0;
+    int ret;
+
+    if (avs->error)
+        return AVERROR_UNKNOWN;
+
+    pkt->destruct = av_destruct_packet;
+
+    // If either stream reaches EOF, try to read the other one before giving up.
+    avisynth_next_stream(s, &st, pkt, &discard);
+    if (st->codec->codec_type == AVMEDIA_TYPE_VIDEO) {
+        ret = avisynth_read_packet_video(s, pkt, discard);
+        if (ret == AVERROR_EOF && avs_has_audio(avs->vi)) {
+            avisynth_next_stream(s, &st, pkt, &discard);
+            return avisynth_read_packet_audio(s, pkt, discard);
+        }
+        return ret;
+    } else {
+        ret = avisynth_read_packet_audio(s, pkt, discard);
+        if (ret == AVERROR_EOF && avs_has_video(avs->vi)) {
+            avisynth_next_stream(s, &st, pkt, &discard);
+            return avisynth_read_packet_video(s, pkt, discard);
+        }
+        return ret;
+    }
+}
+
+static av_cold int avisynth_read_close(AVFormatContext *s) {
+    if (avpriv_lock_avformat())
+        return AVERROR_UNKNOWN;
+
+    avisynth_context_destroy(s->priv_data);
+    avpriv_unlock_avformat();
+    return 0;
+}
+
+static int avisynth_read_seek(AVFormatContext *s, int stream_index, int64_t timestamp, int flags) {
+    AviSynthContext *avs = s->priv_data;
+    AVStream *st;
+    AVRational fps, samplerate;
+
+    if (avs->error)
+        return AVERROR_UNKNOWN;
+
+    fps = (AVRational) {avs->vi->fps_numerator, avs->vi->fps_denominator};
+    samplerate = (AVRational) {avs->vi->audio_samples_per_second, 1};
+
+    st = s->streams[stream_index];
+    if (st->codec->codec_type == AVMEDIA_TYPE_VIDEO) {
+        // AviSynth frame counts are signed int.
+        if ((timestamp >= avs->vi->num_frames) || (timestamp > INT_MAX) || (timestamp < 0))
+            return AVERROR_EOF;
+        avs->curr_frame = timestamp;
+        if (avs_has_audio(avs->vi))
+            avs->curr_sample = av_rescale_q(timestamp, samplerate, fps);
+    } else {
+        if ((timestamp >= avs->vi->num_audio_samples) || (timestamp < 0))
+            return AVERROR_EOF;
+        // Force frame granularity for seeking.
+        if (avs_has_video(avs->vi)) {
+            avs->curr_frame = av_rescale_q(timestamp, fps, samplerate);
+            avs->curr_sample = av_rescale_q(avs->curr_frame, samplerate, fps);
+        } else {
+            avs->curr_sample = timestamp;
+        }
+    }
+
+    return 0;
 }
 
 AVInputFormat ff_avisynth_demuxer = {
     .name           = "avisynth",
-    .long_name      = NULL_IF_CONFIG_SMALL("AVISynth"),
-    .priv_data_size = sizeof(AVISynthContext),
+    .long_name      = NULL_IF_CONFIG_SMALL("AviSynth script"),
+    .priv_data_size = sizeof(AviSynthContext),
     .read_header    = avisynth_read_header,
     .read_packet    = avisynth_read_packet,
     .read_close     = avisynth_read_close,