avformat: AviSynth demuxer rewrite

Directly loads AviSynth through LoadLibrary instead of relying on
Video for Windows, and supports using AvxSynth (via dlopen) to
open scripts on Linux and OS X.

Error messages from AviSynth/AvxSynth are now reported through
av_log and exit, rather than the traditional behavior of generating
an error video that the user would need to watch to diagnose.

The main rewrite was authored by d s <avxsynth.testing@gmail.com>
from the AvxSynth team, with additional contributions by

Oka Motofumi <chikuzen.mo@gmail.com>
Stephen Hutchinson <qyot27@gmail.com>
Diego Biurrun <diego@biurrun.de>
Anton Khirnov <anton@khirnov.net>

Signed-off-by: Anton Khirnov <anton@khirnov.net>

1 files changed, 625 insertions, 166 deletions

diff --git a/libavformat/avisynth.c b/libavformat/avisynth.c
index e411d359b7..10a07401b9 100644
--- a/libavformat/avisynth.c
+++ b/libavformat/avisynth.c
@@ -1,6 +1,6 @@
 /*
- * AviSynth support
- * Copyright (c) 2006 DivX, Inc.
+ * AviSynth/AvxSynth support
+ * Copyright (c) 2012 AvxSynth Team.
  *
  * This file is part of Libav.
  *
@@ -19,211 +19,670 @@
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */
 
-#include <windows.h>
-#include <vfw.h>
-
 #include "libavutil/internal.h"
+#include "libavcodec/internal.h"
 #include "avformat.h"
 #include "internal.h"
-#include "riff.h"
-
-typedef struct {
-    PAVISTREAM handle;
-    AVISTREAMINFO info;
-    DWORD read;
-    LONG chunck_size;
-    LONG chunck_samples;
-} AviSynthStream;
-
-typedef struct {
-    PAVIFILE file;
-    AviSynthStream *streams;
-    int nb_streams;
-    int next_stream;
+
+/* Enable function pointer definitions for runtime loading. */
+#define AVSC_NO_DECLSPEC
+
+/* Platform-specific directives for AviSynth vs AvxSynth.
+ *
+ * avisynth_c.h needs to be the one provided with x264, as
+ * the one in AviSynth's CVS hasn't been updated to support
+ * 2.6's extra colorspaces. A temporary source of that header,
+ * installable from a GNU-style Makefile is available from
+ * github.com/qyot27/avisynth_headers -- AvxSynth doesn't
+ * require this kind of special treatment because like any
+ * standard *nix application, it installs its headers
+ * alongside its libs. */
+#ifdef _WIN32
+  #include <windows.h>
+  #undef EXTERN_C
+  #include <avisynth/avisynth_c.h>
+  #define AVISYNTH_LIB "avisynth"
+  #define USING_AVISYNTH
+#else
+  #include <dlfcn.h>
+  #include <avxsynth/avxsynth_c.h>
+    #if defined (__APPLE__)
+      #define AVISYNTH_LIB "libavxsynth.dylib"
+    #else
+      #define AVISYNTH_LIB "libavxsynth.so"
+    #endif
+
+  #define LoadLibrary(x) dlopen(x, RTLD_NOW | RTLD_GLOBAL)
+  #define GetProcAddress dlsym
+  #define FreeLibrary dlclose
+#endif
+
+typedef struct AviSynthLibrary {
+    void *library;
+#define AVSC_DECLARE_FUNC(name) name ## _func name
+    AVSC_DECLARE_FUNC(avs_bit_blt);
+    AVSC_DECLARE_FUNC(avs_clip_get_error);
+    AVSC_DECLARE_FUNC(avs_create_script_environment);
+    AVSC_DECLARE_FUNC(avs_delete_script_environment);
+    AVSC_DECLARE_FUNC(avs_get_audio);
+    AVSC_DECLARE_FUNC(avs_get_error);
+    AVSC_DECLARE_FUNC(avs_get_frame);
+    AVSC_DECLARE_FUNC(avs_get_version);
+    AVSC_DECLARE_FUNC(avs_get_video_info);
+    AVSC_DECLARE_FUNC(avs_invoke);
+    AVSC_DECLARE_FUNC(avs_release_clip);
+    AVSC_DECLARE_FUNC(avs_release_value);
+    AVSC_DECLARE_FUNC(avs_release_video_frame);
+    AVSC_DECLARE_FUNC(avs_take_clip);
+#undef AVSC_DECLARE_FUNC
+} AviSynthLibrary;
+
+typedef struct AviSynthContext {
+    AVS_ScriptEnvironment *env;
+    AVS_Clip *clip;
+    const AVS_VideoInfo *vi;
+
+    /* avisynth_read_packet_video() iterates over this. */
+    int n_planes;
+    const int *planes;
+
+    int curr_stream;
+    int curr_frame;
+    int64_t curr_sample;
+
+    int error;
+
+    /* Linked list pointers. */
+    struct AviSynthContext *next;
 } AviSynthContext;
 
-static int avisynth_read_header(AVFormatContext *s)
+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;
+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.library = LoadLibrary(AVISYNTH_LIB);
+    if (!avs_library.library)
+        return AVERROR_UNKNOWN;
+
+#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_bit_blt, 0);
+    LOAD_AVS_FUNC(avs_clip_get_error, 0);
+    LOAD_AVS_FUNC(avs_create_script_environment, 0);
+    LOAD_AVS_FUNC(avs_delete_script_environment, 0);
+    LOAD_AVS_FUNC(avs_get_audio, 0);
+    LOAD_AVS_FUNC(avs_get_error, 1); // New to AviSynth 2.6
+    LOAD_AVS_FUNC(avs_get_frame, 0);
+    LOAD_AVS_FUNC(avs_get_version, 0);
+    LOAD_AVS_FUNC(avs_get_video_info, 0);
+    LOAD_AVS_FUNC(avs_invoke, 0);
+    LOAD_AVS_FUNC(avs_release_clip, 0);
+    LOAD_AVS_FUNC(avs_release_value, 0);
+    LOAD_AVS_FUNC(avs_release_video_frame, 0);
+    LOAD_AVS_FUNC(avs_take_clip, 0);
+#undef LOAD_AVS_FUNC
+
+    atexit(avisynth_atexit_handler);
+    return 0;
+
+fail:
+    FreeLibrary(avs_library.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 = 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 cannot accept UTF-8 file names. */
-    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", 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", 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 &&
-            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;
-
-                st->codec->width  = imgfmt.bmiHeader.biWidth;
-                st->codec->height = imgfmt.bmiHeader.biHeight;
-
-                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);
-
-                st->duration = stream->info.dwLength;
-            } else {
-                AVIStreamRelease(stream->handle);
-                continue;
-            }
-
-            avs->nb_streams++;
-
-            st->codec->stream_codec_tag = stream->info.fccHandler;
-
-            avpriv_set_pts_info(st, 64, info.dwScale, info.dwRate);
-            st->start_time = stream->info.dwStart;
+    int ret;
+
+    if (!avs_library.library)
+        if (ret = avisynth_load_library())
+            return ret;
+
+    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);
+            return AVERROR_UNKNOWN;
         }
     }
 
+    if (!avs_ctx_list) {
+        avs_ctx_list = avs;
+    } else {
+        avs->next    = avs_ctx_list;
+        avs_ctx_list = avs;
+    }
+
     return 0;
 }
 
-static int avisynth_read_packet(AVFormatContext *s, AVPacket *pkt)
+static av_cold void avisynth_context_destroy(AviSynthContext *avs)
+{
+    if (avs_atexit_called)
+        return;
+
+    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;
+    }
+
+    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 av_cold void avisynth_atexit_handler(void)
+{
+    AviSynthContext *avs = avs_ctx_list;
+
+    while (avs) {
+        AviSynthContext *next = avs->next;
+        avisynth_context_destroy(avs);
+        avs = next;
+    }
+    FreeLibrary(avs_library.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   = AV_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 USING_AVISYNTH
+    case AVS_CS_YV24:
+        st->codec->pix_fmt = AV_PIX_FMT_YUV444P;
+        planar             = 1;
+        break;
+    case AVS_CS_YV16:
+        st->codec->pix_fmt = AV_PIX_FMT_YUV422P;
+        planar             = 1;
+        break;
+    case AVS_CS_YV411:
+        st->codec->pix_fmt = AV_PIX_FMT_YUV411P;
+        planar             = 1;
+        break;
+    case AVS_CS_Y8:
+        st->codec->pix_fmt = AV_PIX_FMT_GRAY8;
+        planar             = 2;
+        break;
+#endif
+    case AVS_CS_BGR24:
+        st->codec->pix_fmt = AV_PIX_FMT_BGR24;
+        break;
+    case AVS_CS_BGR32:
+        st->codec->pix_fmt = AV_PIX_FMT_RGB32;
+        break;
+    case AVS_CS_YUY2:
+        st->codec->pix_fmt = AV_PIX_FMT_YUYV422;
+        break;
+    case AVS_CS_YV12:
+        st->codec->pix_fmt = AV_PIX_FMT_YUV420P;
+        planar             = 1;
+        break;
+    case AVS_CS_I420: // Is this even used anywhere?
+        st->codec->pix_fmt = AV_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;
+    }
+
+    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 = AV_CODEC_ID_PCM_U8;
+        break;
+    case AVS_SAMPLE_INT16:
+        st->codec->codec_id = AV_CODEC_ID_PCM_S16LE;
+        break;
+    case AVS_SAMPLE_INT24:
+        st->codec->codec_id = AV_CODEC_ID_PCM_S24LE;
+        break;
+    case AVS_SAMPLE_INT32:
+        st->codec->codec_id = AV_CODEC_ID_PCM_S32LE;
+        break;
+    case AVS_SAMPLE_FLOAT:
+        st->codec->codec_id = AV_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 = s->priv_data;
-    HRESULT res;
-    AviSynthStream *stream;
-    int stream_id = avs->next_stream;
-    LONG read_size;
+    AVS_Value arg, val;
+    int ret;
+#ifdef USING_AVISYNTH
+    char filename_ansi[MAX_PATH * 4];
+    wchar_t filename_wc[MAX_PATH * 4];
+#endif
+
+    if (ret = avisynth_context_create(s))
+        return ret;
+
+#ifdef USING_AVISYNTH
+    /* Convert UTF-8 to ANSI code page */
+    MultiByteToWideChar(CP_UTF8, 0, s->filename, -1, filename_wc, MAX_PATH * 4);
+    WideCharToMultiByte(CP_THREAD_ACP, 0, filename_wc, -1, filename_ansi,
+                        MAX_PATH * 4, NULL, NULL);
+    arg = avs_new_value_string(filename_ansi);
+#else
+    arg = avs_new_value_string(s->filename);
+#endif
+    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, "AviSynth script did not return a clip\n");
+        ret = AVERROR_UNKNOWN;
+        goto fail;
+    }
 
-    // handle interleaving manually...
-    stream = &avs->streams[stream_id];
+    avs->clip = avs_library.avs_take_clip(val, avs->env);
+    avs->vi   = avs_library.avs_get_video_info(avs->clip);
 
-    if (stream->read >= stream->info.dwLength)
-        return AVERROR(EIO);
+#ifdef USING_AVISYNTH
+    /* libav only supports AviSynth 2.6 on Windows. Since AvxSynth
+     * identifies itself as interface version 3 like 2.5.8, this
+     * needs to be special-cased. */
+
+    if (avs_library.avs_get_version(avs->clip) == 3) {
+        av_log(s, AV_LOG_ERROR,
+               "AviSynth 2.5.8 not supported. Please upgrade to 2.6.\n");
+        ret = AVERROR_UNKNOWN;
+        goto fail;
+    }
+#endif
 
-    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;
+    /* 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;
 
-    res = AVIStreamRead(stream->handle, stream->read, stream->chunck_samples,
-                        pkt->data, stream->chunck_size, &read_size, NULL);
+fail:
+    avisynth_context_destroy(avs);
+    return ret;
+}
 
-    pkt->pts  = stream->read;
-    pkt->size = read_size;
+static void avisynth_next_stream(AVFormatContext *s, AVStream **st,
+                                 AVPacket *pkt, int *discard)
+{
+    AviSynthContext *avs = s->priv_data;
 
-    stream->read += stream->chunck_samples;
+    pkt->stream_index = avs->curr_stream++;
+    avs->curr_stream %= s->nb_streams;
 
-    // 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);
+    *st = s->streams[pkt->stream_index];
+    if ((*st)->discard == AVDISCARD_ALL)
+        *discard = 1;
+    else
+        *discard = 0;
 
-    return (res == S_OK) ? pkt->size : -1;
+    return;
 }
 
-static int avisynth_read_close(AVFormatContext *s)
+/* Copy AviSynth clip data into an AVPacket. */
+static int avisynth_read_packet_video(AVFormatContext *s, AVPacket *pkt,
+                                      int discard)
 {
     AviSynthContext *avs = s->priv_data;
-    int i;
+    AVS_VideoFrame *frame;
+    unsigned char *dst_p;
+    const unsigned char *src_p;
+    int n, 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. */
+    n = avs->curr_frame++;
+    if (discard)
+        return 0;
+
+    pkt->pts      = n;
+    pkt->dts      = n;
+    pkt->duration = 1;
+
+#ifdef USING_AVISYNTH
+    /* Define the bpp values for the new AviSynth 2.6 colorspaces.
+     * Since AvxSynth doesn't have these functions, special-case
+     * it in order to avoid implicit declaration errors. */
+
+    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
+#endif
+        bits = avs_bits_per_pixel(avs->vi);
+
+    /* Without the 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;
+
+    if (av_new_packet(pkt, pkt->size) < 0)
+        return AVERROR(ENOMEM);
+
+    frame = avs_library.avs_get_frame(avs->clip, n);
+    error = avs_library.avs_clip_get_error(avs->clip);
+    if (error) {
+        av_log(s, AV_LOG_ERROR, "%s\n", error);
+        avs->error = 1;
+        av_packet_unref(pkt);
+        return AVERROR_UNKNOWN;
+    }
 
-    for (i = 0; i < avs->nb_streams; i++)
-        AVIStreamRelease(avs->streams[i].handle);
+    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);
+        pitch = avs_get_pitch_p(frame, plane);
+
+        rowsize     = avs_get_row_size_p(frame, plane);
+        planeheight = avs_get_height_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;
+        }
 
-    av_free(avs->streams);
-    AVIFileRelease(avs->file);
-    AVIFileExit();
+        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_seek(AVFormatContext *s, int stream_index,
-                              int64_t pts, int flags)
+static int avisynth_read_packet_audio(AVFormatContext *s, AVPacket *pkt,
+                                      int discard)
 {
     AviSynthContext *avs = s->priv_data;
-    int stream_id;
+    AVRational fps, samplerate;
+    int samples;
+    int64_t n;
+    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. */
+    n                 = avs->curr_sample;
+    avs->curr_sample += samples;
+    if (discard)
+        return 0;
+
+    pkt->pts      = n;
+    pkt->dts      = n;
+    pkt->duration = samples;
+
+    pkt->size = avs_bytes_per_channel_sample(avs->vi) *
+                samples * avs->vi->nchannels;
+    if (!pkt->size)
+        return AVERROR_UNKNOWN;
+
+    if (av_new_packet(pkt, pkt->size) < 0)
+        return AVERROR(ENOMEM);
+
+    avs_library.avs_get_audio(avs->clip, pkt->data, n, 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_packet_unref(pkt);
+        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;
 
-    for (stream_id = 0; stream_id < avs->nb_streams; stream_id++)
-        avs->streams[stream_id].read =
-            pts * avs->streams[stream_id].chunck_samples;
+    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;
+
+    /* 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);
+        }
+    } 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"),
+    .long_name      = NULL_IF_CONFIG_SMALL("AviSynth script"),
     .priv_data_size = sizeof(AviSynthContext),
     .read_header    = avisynth_read_header,
     .read_packet    = avisynth_read_packet,