FFmpeg/libavformat/imfdec.c

/*
 * 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
 */

/*
 *
 * Copyright (c) Sandflow Consulting LLC
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * * Redistributions of source code must retain the above copyright notice, this
 *   list of conditions and the following disclaimer.
 * * Redistributions in binary form must reproduce the above copyright notice,
 *   this list of conditions and the following disclaimer in the documentation
 *   and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */

/**
 * Demuxes an IMF Composition
 *
 * References
 * OV 2067-0:2018 - SMPTE Overview Document - Interoperable Master Format
 * ST 2067-2:2020 - SMPTE Standard - Interoperable Master Format — Core Constraints
 * ST 2067-3:2020 - SMPTE Standard - Interoperable Master Format — Composition Playlist
 * ST 2067-5:2020 - SMPTE Standard - Interoperable Master Format — Essence Component
 * ST 2067-20:2016 - SMPTE Standard - Interoperable Master Format — Application #2
 * ST 2067-21:2020 - SMPTE Standard - Interoperable Master Format — Application #2 Extended
 * ST 2067-102:2017 - SMPTE Standard - Interoperable Master Format — Common Image Pixel Color Schemes
 * ST 429-9:2007 - SMPTE Standard - D-Cinema Packaging — Asset Mapping and File Segmentation
 *
 * @author Marc-Antoine Arnaud
 * @author Valentin Noel
 * @author Nicholas Vanderzwet
 * @file
 * @ingroup lavu_imf
 */

#include "avio_internal.h"
#include "demux.h"
#include "imf.h"
#include "internal.h"
#include "libavcodec/packet.h"
#include "libavutil/avstring.h"
#include "libavutil/bprint.h"
#include "libavutil/intreadwrite.h"
#include "libavutil/opt.h"
#include "mxf.h"
#include <inttypes.h>
#include <libxml/parser.h>

#define AVRATIONAL_FORMAT "%d/%d"
#define AVRATIONAL_ARG(rational) rational.num, rational.den

/**
 * IMF Asset locator
 */
typedef struct IMFAssetLocator {
    FFIMFUUID uuid;
    char *absolute_uri;
} IMFAssetLocator;

/**
 * IMF Asset locator map
 * Results from the parsing of one or more ASSETMAP XML files
 */
typedef struct IMFAssetLocatorMap {
    uint32_t asset_count;
    IMFAssetLocator *assets;
} IMFAssetLocatorMap;

typedef struct IMFVirtualTrackResourcePlaybackCtx {
    IMFAssetLocator *locator;          /**< Location of the resource */
    FFIMFTrackFileResource *resource;  /**< Underlying IMF CPL resource */
    AVFormatContext *ctx;              /**< Context associated with the resource */
    AVRational start_time;             /**< inclusive start time of the resource on the CPL timeline (s) */
    AVRational end_time;               /**< exclusive end time of the resource on the CPL timeline (s) */
    AVRational ts_offset;              /**< start_time minus the entry point into the resource (s) */
} IMFVirtualTrackResourcePlaybackCtx;

typedef struct IMFVirtualTrackPlaybackCtx {
    int32_t index;                                 /**< Track index in playlist */
    AVRational current_timestamp;                  /**< Current temporal position */
    AVRational duration;                           /**< Overall duration */
    uint32_t resource_count;                       /**< Number of resources (<= INT32_MAX) */
    unsigned int resources_alloc_sz;               /**< Size of the buffer holding the resource */
    IMFVirtualTrackResourcePlaybackCtx *resources; /**< Buffer holding the resources */
    int32_t current_resource_index;                /**< Index of the current resource in resources,
                                                        or < 0 if a current resource has yet to be selected */
} IMFVirtualTrackPlaybackCtx;

typedef struct IMFContext {
    const AVClass *class;
    const char *base_url;
    char *asset_map_paths;
    AVIOInterruptCB *interrupt_callback;
    AVDictionary *avio_opts;
    FFIMFCPL *cpl;
    IMFAssetLocatorMap asset_locator_map;
    uint32_t track_count;
    IMFVirtualTrackPlaybackCtx **tracks;
} IMFContext;

static int imf_uri_is_url(const char *string)
{
    return strstr(string, "://") != NULL;
}

static int imf_uri_is_unix_abs_path(const char *string)
{
    return string[0] == '/';
}

static int imf_uri_is_dos_abs_path(const char *string)
{
    /* Absolute path case: `C:\path\to\somwhere` */
    if (string[1] == ':' && string[2] == '\\')
        return 1;

    /* Absolute path case: `C:/path/to/somwhere` */
    if (string[1] == ':' && string[2] == '/')
        return 1;

    /* Network path case: `\\path\to\somwhere` */
    if (string[0] == '\\' && string[1] == '\\')
        return 1;

    return 0;
}

static int imf_time_to_ts(int64_t *ts, AVRational t, AVRational time_base)
{
    int dst_num;
    int dst_den;
    AVRational r;

    r = av_div_q(t, time_base);

    if ((av_reduce(&dst_num, &dst_den, r.num, r.den, INT64_MAX) != 1))
        return 1;

    if (dst_den != 1)
        return 1;

    *ts = dst_num;

    return 0;
}

/**
 * Parse a ASSETMAP XML file to extract the UUID-URI mapping of assets.
 * @param s the current format context, if any (can be NULL).
 * @param doc the XML document to be parsed.
 * @param asset_map pointer on the IMFAssetLocatorMap to fill.
 * @param base_url the url of the asset map XML file, if any (can be NULL).
 * @return a negative value in case of error, 0 otherwise.
 */
static int parse_imf_asset_map_from_xml_dom(AVFormatContext *s,
                                            xmlDocPtr doc,
                                            IMFAssetLocatorMap *asset_map,
                                            const char *base_url)
{
    xmlNodePtr asset_map_element = NULL;
    xmlNodePtr node = NULL;
    xmlNodePtr asset_element = NULL;
    unsigned long elem_count;
    char *uri;
    int ret = 0;
    IMFAssetLocator *asset = NULL;
    void *tmp;

    asset_map_element = xmlDocGetRootElement(doc);

    if (!asset_map_element) {
        av_log(s, AV_LOG_ERROR, "Unable to parse asset map XML - missing root node\n");
        return AVERROR_INVALIDDATA;
    }

    if (asset_map_element->type != XML_ELEMENT_NODE || av_strcasecmp(asset_map_element->name, "AssetMap")) {
        av_log(s, AV_LOG_ERROR, "Unable to parse asset map XML - wrong root node name[%s] type[%d]\n",
               asset_map_element->name, (int)asset_map_element->type);
        return AVERROR_INVALIDDATA;
    }

    /* parse asset locators */
    if (!(node = ff_imf_xml_get_child_element_by_name(asset_map_element, "AssetList"))) {
        av_log(s, AV_LOG_ERROR, "Unable to parse asset map XML - missing AssetList node\n");
        return AVERROR_INVALIDDATA;
    }
    elem_count = xmlChildElementCount(node);
    if (elem_count > UINT32_MAX
        || asset_map->asset_count > UINT32_MAX - elem_count)
        return AVERROR(ENOMEM);
    tmp = av_realloc_array(asset_map->assets,
                           elem_count + asset_map->asset_count,
                           sizeof(IMFAssetLocator));
    if (!tmp) {
        av_log(s, AV_LOG_ERROR, "Cannot allocate IMF asset locators\n");
        return AVERROR(ENOMEM);
    }
    asset_map->assets = tmp;

    asset_element = xmlFirstElementChild(node);
    while (asset_element) {
        if (av_strcasecmp(asset_element->name, "Asset") != 0)
            continue;

        asset = &(asset_map->assets[asset_map->asset_count]);

        if (ff_imf_xml_read_uuid(ff_imf_xml_get_child_element_by_name(asset_element, "Id"), asset->uuid)) {
            av_log(s, AV_LOG_ERROR, "Could not parse UUID from asset in asset map.\n");
            return AVERROR_INVALIDDATA;
        }

        av_log(s, AV_LOG_DEBUG, "Found asset id: " FF_IMF_UUID_FORMAT "\n", UID_ARG(asset->uuid));

        if (!(node = ff_imf_xml_get_child_element_by_name(asset_element, "ChunkList"))) {
            av_log(s, AV_LOG_ERROR, "Unable to parse asset map XML - missing ChunkList node\n");
            return AVERROR_INVALIDDATA;
        }

        if (!(node = ff_imf_xml_get_child_element_by_name(node, "Chunk"))) {
            av_log(s, AV_LOG_ERROR, "Unable to parse asset map XML - missing Chunk node\n");
            return AVERROR_INVALIDDATA;
        }

        uri = xmlNodeGetContent(ff_imf_xml_get_child_element_by_name(node, "Path"));
        if (!imf_uri_is_url(uri) && !imf_uri_is_unix_abs_path(uri) && !imf_uri_is_dos_abs_path(uri))
            asset->absolute_uri = av_append_path_component(base_url, uri);
        else
            asset->absolute_uri = av_strdup(uri);
        xmlFree(uri);
        if (!asset->absolute_uri)
            return AVERROR(ENOMEM);

        av_log(s, AV_LOG_DEBUG, "Found asset absolute URI: %s\n", asset->absolute_uri);

        asset_map->asset_count++;
        asset_element = xmlNextElementSibling(asset_element);
    }

    return ret;
}

/**
 * Initializes an IMFAssetLocatorMap structure.
 */
static void imf_asset_locator_map_init(IMFAssetLocatorMap *asset_map)
{
    asset_map->assets = NULL;
    asset_map->asset_count = 0;
}

/**
 * Free a IMFAssetLocatorMap pointer.
 */
static void imf_asset_locator_map_deinit(IMFAssetLocatorMap *asset_map)
{
    for (uint32_t i = 0; i < asset_map->asset_count; i++)
        av_freep(&asset_map->assets[i].absolute_uri);

    av_freep(&asset_map->assets);
}

static int parse_assetmap(AVFormatContext *s, const char *url)
{
    IMFContext *c = s->priv_data;
    AVIOContext *in = NULL;
    struct AVBPrint buf;
    AVDictionary *opts = NULL;
    xmlDoc *doc = NULL;
    const char *base_url;
    char *tmp_str = NULL;
    int ret;

    av_log(s, AV_LOG_DEBUG, "Asset Map URL: %s\n", url);

    av_dict_copy(&opts, c->avio_opts, 0);
    ret = s->io_open(s, &in, url, AVIO_FLAG_READ, &opts);
    av_dict_free(&opts);
    if (ret < 0)
        return ret;

    av_bprint_init(&buf, 0, INT_MAX); // xmlReadMemory uses integer length

    ret = avio_read_to_bprint(in, &buf, SIZE_MAX);
    if (ret < 0 || !avio_feof(in)) {
        av_log(s, AV_LOG_ERROR, "Unable to read to asset map '%s'\n", url);
        if (ret == 0)
            ret = AVERROR_INVALIDDATA;
        goto clean_up;
    }

    LIBXML_TEST_VERSION

    tmp_str = av_strdup(url);
    if (!tmp_str) {
        ret = AVERROR(ENOMEM);
        goto clean_up;
    }
    base_url = av_dirname(tmp_str);

    doc = xmlReadMemory(buf.str, buf.len, url, NULL, 0);

    ret = parse_imf_asset_map_from_xml_dom(s, doc, &c->asset_locator_map, base_url);
    if (!ret)
        av_log(s, AV_LOG_DEBUG, "Found %d assets from %s\n",
               c->asset_locator_map.asset_count, url);

    xmlFreeDoc(doc);

clean_up:
    if (tmp_str)
        av_freep(&tmp_str);
    ff_format_io_close(s, &in);
    av_bprint_finalize(&buf, NULL);
    return ret;
}

static IMFAssetLocator *find_asset_map_locator(IMFAssetLocatorMap *asset_map, FFIMFUUID uuid)
{
    for (uint32_t i = 0; i < asset_map->asset_count; i++) {
        if (memcmp(asset_map->assets[i].uuid, uuid, 16) == 0)
            return &(asset_map->assets[i]);
    }
    return NULL;
}

static int open_track_resource_context(AVFormatContext *s,
                                       IMFVirtualTrackPlaybackCtx *track,
                                       int32_t resource_index)
{
    IMFContext *c = s->priv_data;
    int ret = 0;
    int64_t seek_offset = 0;
    AVDictionary *opts = NULL;
    AVStream *st;
    IMFVirtualTrackResourcePlaybackCtx *track_resource = track->resources + resource_index;

    if (track_resource->ctx) {
        av_log(s, AV_LOG_DEBUG, "Input context already opened for %s.\n",
               track_resource->locator->absolute_uri);
        return 0;
    }

    track_resource->ctx = avformat_alloc_context();
    if (!track_resource->ctx)
        return AVERROR(ENOMEM);

    track_resource->ctx->io_open = s->io_open;
    track_resource->ctx->io_close = s->io_close;
    track_resource->ctx->io_close2 = s->io_close2;
    track_resource->ctx->flags |= s->flags & ~AVFMT_FLAG_CUSTOM_IO;

    if ((ret = ff_copy_whiteblacklists(track_resource->ctx, s)) < 0)
        goto cleanup;

    if ((ret = av_opt_set(track_resource->ctx, "format_whitelist", "mxf", 0)))
        goto cleanup;

    if ((ret = av_dict_copy(&opts, c->avio_opts, 0)) < 0)
        goto cleanup;

    ret = avformat_open_input(&track_resource->ctx,
                              track_resource->locator->absolute_uri,
                              NULL,
                              &opts);
    if (ret < 0) {
        av_log(s, AV_LOG_ERROR, "Could not open %s input context: %s\n",
               track_resource->locator->absolute_uri, av_err2str(ret));
        goto cleanup;
    }
    av_dict_free(&opts);

    /* make sure there is only one stream in the file */

    if (track_resource->ctx->nb_streams != 1) {
        ret = AVERROR_INVALIDDATA;
        goto cleanup;
    }

    st = track_resource->ctx->streams[0];

    /* Determine the seek offset into the Track File, taking into account:
     * - the current timestamp within the virtual track
     * - the entry point of the resource
     */
    if (imf_time_to_ts(&seek_offset,
                       av_sub_q(track->current_timestamp, track_resource->ts_offset),
                       st->time_base))
        av_log(s, AV_LOG_WARNING, "Incoherent stream timebase " AVRATIONAL_FORMAT
               "and composition timeline position: " AVRATIONAL_FORMAT "\n",
               AVRATIONAL_ARG(st->time_base), AVRATIONAL_ARG(track->current_timestamp));

    if (seek_offset) {
        av_log(s, AV_LOG_DEBUG, "Seek at resource %s entry point: %" PRIi64 "\n",
               track_resource->locator->absolute_uri, seek_offset);
        ret = avformat_seek_file(track_resource->ctx, 0, seek_offset, seek_offset, seek_offset, 0);
        if (ret < 0) {
            av_log(s,
                   AV_LOG_ERROR,
                   "Could not seek at %" PRId64 "on %s: %s\n",
                   seek_offset,
                   track_resource->locator->absolute_uri,
                   av_err2str(ret));
            avformat_close_input(&track_resource->ctx);
            return ret;
        }
    }

    return 0;

cleanup:
    av_dict_free(&opts);
    avformat_free_context(track_resource->ctx);
    track_resource->ctx = NULL;
    return ret;
}

static int open_track_file_resource(AVFormatContext *s,
                                    FFIMFTrackFileResource *track_file_resource,
                                    IMFVirtualTrackPlaybackCtx *track)
{
    IMFContext *c = s->priv_data;
    IMFAssetLocator *asset_locator;
    void *tmp;

    asset_locator = find_asset_map_locator(&c->asset_locator_map, track_file_resource->track_file_uuid);
    if (!asset_locator) {
        av_log(s, AV_LOG_ERROR, "Could not find asset locator for UUID: " FF_IMF_UUID_FORMAT "\n",
               UID_ARG(track_file_resource->track_file_uuid));
        return AVERROR_INVALIDDATA;
    }

    av_log(s,
           AV_LOG_DEBUG,
           "Found locator for " FF_IMF_UUID_FORMAT ": %s\n",
           UID_ARG(asset_locator->uuid),
           asset_locator->absolute_uri);

    if (track->resource_count > INT32_MAX - track_file_resource->base.repeat_count
        || (track->resource_count + track_file_resource->base.repeat_count)
            > INT_MAX / sizeof(IMFVirtualTrackResourcePlaybackCtx))
        return AVERROR(ENOMEM);
    tmp = av_fast_realloc(track->resources,
                          &track->resources_alloc_sz,
                          (track->resource_count + track_file_resource->base.repeat_count)
                              * sizeof(IMFVirtualTrackResourcePlaybackCtx));
    if (!tmp)
        return AVERROR(ENOMEM);
    track->resources = tmp;

    for (uint32_t i = 0; i < track_file_resource->base.repeat_count; i++) {
        IMFVirtualTrackResourcePlaybackCtx vt_ctx;

        vt_ctx.locator = asset_locator;
        vt_ctx.resource = track_file_resource;
        vt_ctx.ctx = NULL;
        vt_ctx.start_time = track->duration;
        vt_ctx.ts_offset = av_sub_q(vt_ctx.start_time,
                                    av_div_q(av_make_q((int)track_file_resource->base.entry_point, 1),
                                             track_file_resource->base.edit_rate));
        vt_ctx.end_time = av_add_q(track->duration,
                                   av_make_q((int)track_file_resource->base.duration
                                                 * track_file_resource->base.edit_rate.den,
                                             track_file_resource->base.edit_rate.num));
        track->resources[track->resource_count++] = vt_ctx;
        track->duration = vt_ctx.end_time;
    }

    return 0;
}

static void imf_virtual_track_playback_context_deinit(IMFVirtualTrackPlaybackCtx *track)
{
    for (uint32_t i = 0; i < track->resource_count; i++)
        avformat_close_input(&track->resources[i].ctx);

    av_freep(&track->resources);
}

static int open_virtual_track(AVFormatContext *s,
                              FFIMFTrackFileVirtualTrack *virtual_track,
                              int32_t track_index)
{
    IMFContext *c = s->priv_data;
    IMFVirtualTrackPlaybackCtx *track = NULL;
    void *tmp;
    int ret = 0;

    if (!(track = av_mallocz(sizeof(IMFVirtualTrackPlaybackCtx))))
        return AVERROR(ENOMEM);
    track->current_resource_index = -1;
    track->index = track_index;
    track->duration = av_make_q(0, 1);

    for (uint32_t i = 0; i < virtual_track->resource_count; i++) {
        av_log(s,
               AV_LOG_DEBUG,
               "Open stream from file " FF_IMF_UUID_FORMAT ", stream %d\n",
               UID_ARG(virtual_track->resources[i].track_file_uuid),
               i);
        if ((ret = open_track_file_resource(s, &virtual_track->resources[i], track)) != 0) {
            av_log(s,
                   AV_LOG_ERROR,
                   "Could not open image track resource " FF_IMF_UUID_FORMAT "\n",
                   UID_ARG(virtual_track->resources[i].track_file_uuid));
            goto clean_up;
        }
    }

    track->current_timestamp = av_make_q(0, track->duration.den);

    if (c->track_count == UINT32_MAX) {
        ret = AVERROR(ENOMEM);
        goto clean_up;
    }
    tmp = av_realloc_array(c->tracks, c->track_count + 1, sizeof(IMFVirtualTrackPlaybackCtx *));
    if (!tmp) {
        ret = AVERROR(ENOMEM);
        goto clean_up;
    }
    c->tracks = tmp;
    c->tracks[c->track_count++] = track;

    return 0;

clean_up:
    imf_virtual_track_playback_context_deinit(track);
    av_free(track);
    return ret;
}

static int set_context_streams_from_tracks(AVFormatContext *s)
{
    IMFContext *c = s->priv_data;
    int ret = 0;

    for (uint32_t i = 0; i < c->track_count; i++) {
        AVStream *asset_stream;
        AVStream *first_resource_stream;

        /* Open the first resource of the track to get stream information */
        ret = open_track_resource_context(s, c->tracks[i], 0);
        if (ret)
            return ret;
        first_resource_stream = c->tracks[i]->resources[0].ctx->streams[0];
        av_log(s, AV_LOG_DEBUG, "Open the first resource of track %d\n", c->tracks[i]->index);

        /* Copy stream information */
        asset_stream = avformat_new_stream(s, NULL);
        if (!asset_stream) {
            av_log(s, AV_LOG_ERROR, "Could not create stream\n");
            return AVERROR(ENOMEM);
        }
        asset_stream->id = i;
        ret = avcodec_parameters_copy(asset_stream->codecpar, first_resource_stream->codecpar);
        if (ret < 0) {
            av_log(s, AV_LOG_ERROR, "Could not copy stream parameters\n");
            return ret;
        }
        avpriv_set_pts_info(asset_stream,
                            first_resource_stream->pts_wrap_bits,
                            first_resource_stream->time_base.num,
                            first_resource_stream->time_base.den);
        asset_stream->duration = (int64_t)av_q2d(av_mul_q(c->tracks[i]->duration,
                                                          av_inv_q(asset_stream->time_base)));
    }

    return 0;
}

static int open_cpl_tracks(AVFormatContext *s)
{
    IMFContext *c = s->priv_data;
    int32_t track_index = 0;
    int ret;

    if (c->cpl->main_image_2d_track) {
        if ((ret = open_virtual_track(s, c->cpl->main_image_2d_track, track_index++)) != 0) {
            av_log(s, AV_LOG_ERROR, "Could not open image track " FF_IMF_UUID_FORMAT "\n",
                   UID_ARG(c->cpl->main_image_2d_track->base.id_uuid));
            return ret;
        }
    }

    for (uint32_t i = 0; i < c->cpl->main_audio_track_count; i++) {
        if ((ret = open_virtual_track(s, &c->cpl->main_audio_tracks[i], track_index++)) != 0) {
            av_log(s, AV_LOG_ERROR, "Could not open audio track " FF_IMF_UUID_FORMAT "\n",
                   UID_ARG(c->cpl->main_audio_tracks[i].base.id_uuid));
            return ret;
        }
    }

    return set_context_streams_from_tracks(s);
}

static int imf_read_header(AVFormatContext *s)
{
    IMFContext *c = s->priv_data;
    char *asset_map_path;
    char *tmp_str;
    int ret = 0;

    c->interrupt_callback = &s->interrupt_callback;
    tmp_str = av_strdup(s->url);
    if (!tmp_str)
        return AVERROR(ENOMEM);
    c->base_url = av_strdup(av_dirname(tmp_str));
    av_freep(&tmp_str);
    if (!c->base_url)
        return AVERROR(ENOMEM);

    if ((ret = ffio_copy_url_options(s->pb, &c->avio_opts)) < 0)
        return ret;

    av_log(s, AV_LOG_DEBUG, "start parsing IMF CPL: %s\n", s->url);

    if ((ret = ff_imf_parse_cpl(s->pb, &c->cpl)) < 0)
        return ret;

    av_log(s,
           AV_LOG_DEBUG,
           "parsed IMF CPL: " FF_IMF_UUID_FORMAT "\n",
           UID_ARG(c->cpl->id_uuid));

    if (!c->asset_map_paths) {
        c->asset_map_paths = av_append_path_component(c->base_url, "ASSETMAP.xml");
        if (!c->asset_map_paths) {
            ret = AVERROR(ENOMEM);
            return ret;
        }
        av_log(s, AV_LOG_DEBUG, "No asset maps provided, using the default ASSETMAP.xml\n");
    }

    /* Parse each asset map XML file */
    imf_asset_locator_map_init(&c->asset_locator_map);
    asset_map_path = av_strtok(c->asset_map_paths, ",", &tmp_str);
    while (asset_map_path != NULL) {
        av_log(s, AV_LOG_DEBUG, "start parsing IMF Asset Map: %s\n", asset_map_path);

        if ((ret = parse_assetmap(s, asset_map_path)))
            return ret;

        asset_map_path = av_strtok(NULL, ",", &tmp_str);
    }

    av_log(s, AV_LOG_DEBUG, "parsed IMF Asset Maps\n");

    if ((ret = open_cpl_tracks(s)))
        return ret;

    av_log(s, AV_LOG_DEBUG, "parsed IMF package\n");

    return 0;
}

static IMFVirtualTrackPlaybackCtx *get_next_track_with_minimum_timestamp(AVFormatContext *s)
{
    IMFContext *c = s->priv_data;
    IMFVirtualTrackPlaybackCtx *track;

    AVRational minimum_timestamp = av_make_q(INT32_MAX, 1);
    for (uint32_t i = c->track_count; i > 0; i--) {
        av_log(s, AV_LOG_TRACE, "Compare track %d timestamp " AVRATIONAL_FORMAT
               " to minimum " AVRATIONAL_FORMAT
               " (over duration: " AVRATIONAL_FORMAT ")\n", i,
               AVRATIONAL_ARG(c->tracks[i - 1]->current_timestamp),
               AVRATIONAL_ARG(minimum_timestamp),
               AVRATIONAL_ARG(c->tracks[i - 1]->duration));

        if (av_cmp_q(c->tracks[i - 1]->current_timestamp, minimum_timestamp) <= 0) {
            track = c->tracks[i - 1];
            minimum_timestamp = track->current_timestamp;
        }
    }

    av_log(s, AV_LOG_DEBUG, "Found next track to read: %d (timestamp: %lf / %lf)\n",
           track->index, av_q2d(track->current_timestamp), av_q2d(minimum_timestamp));
    return track;
}

static int get_resource_context_for_timestamp(AVFormatContext *s, IMFVirtualTrackPlaybackCtx *track, IMFVirtualTrackResourcePlaybackCtx **resource)
{
    *resource = NULL;

    if (av_cmp_q(track->current_timestamp, track->duration) >= 0) {
        av_log(s, AV_LOG_DEBUG, "Reached the end of the virtual track\n");
        return AVERROR_EOF;
    }

    av_log(s,
           AV_LOG_TRACE,
           "Looking for track %d resource for timestamp = %lf / %lf\n",
           track->index,
           av_q2d(track->current_timestamp),
           av_q2d(track->duration));
    for (uint32_t i = 0; i < track->resource_count; i++) {

        if (av_cmp_q(track->resources[i].end_time, track->current_timestamp) > 0) {
            av_log(s, AV_LOG_DEBUG, "Found resource %d in track %d to read at timestamp %lf: "
                   "entry=%" PRIu32 ", duration=%" PRIu32 ", editrate=" AVRATIONAL_FORMAT "\n",
                   i, track->index, av_q2d(track->current_timestamp),
                   track->resources[i].resource->base.entry_point,
                   track->resources[i].resource->base.duration,
                   AVRATIONAL_ARG(track->resources[i].resource->base.edit_rate));

            if (track->current_resource_index != i) {
                int ret;

                av_log(s, AV_LOG_TRACE, "Switch resource on track %d: re-open context\n",
                       track->index);

                ret = open_track_resource_context(s, track, i);
                if (ret != 0)
                    return ret;
                if (track->current_resource_index > 0)
                    avformat_close_input(&track->resources[track->current_resource_index].ctx);
                track->current_resource_index = i;
            }

            *resource = track->resources + track->current_resource_index;
            return 0;
        }
    }

    av_log(s, AV_LOG_ERROR, "Could not find IMF track resource to read\n");
    return AVERROR_STREAM_NOT_FOUND;
}

static int imf_read_packet(AVFormatContext *s, AVPacket *pkt)
{
    IMFVirtualTrackResourcePlaybackCtx *resource = NULL;
    int ret = 0;
    IMFVirtualTrackPlaybackCtx *track;
    int64_t delta_ts;
    AVStream *st;
    AVRational next_timestamp;

    track = get_next_track_with_minimum_timestamp(s);

    ret = get_resource_context_for_timestamp(s, track, &resource);
    if (ret)
        return ret;

    ret = av_read_frame(resource->ctx, pkt);
    if (ret)
        return ret;

    av_log(s, AV_LOG_DEBUG, "Got packet: pts=%" PRId64 ", dts=%" PRId64
            ", duration=%" PRId64 ", stream_index=%d, pos=%" PRId64
            ", time_base=" AVRATIONAL_FORMAT "\n", pkt->pts, pkt->dts, pkt->duration,
            pkt->stream_index, pkt->pos, AVRATIONAL_ARG(pkt->time_base));

    /* IMF resources contain only one stream */

    if (pkt->stream_index != 0)
        return AVERROR_INVALIDDATA;
    st = resource->ctx->streams[0];

    pkt->stream_index = track->index;

    /* adjust the packet PTS and DTS based on the temporal position of the resource within the timeline */

    ret = imf_time_to_ts(&delta_ts, resource->ts_offset, st->time_base);

    if (!ret) {
        if (pkt->pts != AV_NOPTS_VALUE)
            pkt->pts += delta_ts;
        if (pkt->dts != AV_NOPTS_VALUE)
            pkt->dts += delta_ts;
    } else {
        av_log(s, AV_LOG_WARNING, "Incoherent time stamp " AVRATIONAL_FORMAT
               " for time base " AVRATIONAL_FORMAT,
               AVRATIONAL_ARG(resource->ts_offset),
               AVRATIONAL_ARG(pkt->time_base));
    }

    /* advance the track timestamp by the packet duration */

    next_timestamp = av_add_q(track->current_timestamp,
                              av_mul_q(av_make_q((int)pkt->duration, 1), st->time_base));

    /* if necessary, clamp the next timestamp to the end of the current resource */

    if (av_cmp_q(next_timestamp, resource->end_time) > 0) {

        int64_t new_pkt_dur;

        /* shrink the packet duration */

        ret = imf_time_to_ts(&new_pkt_dur,
                             av_sub_q(resource->end_time, track->current_timestamp),
                             st->time_base);

        if (!ret)
            pkt->duration = new_pkt_dur;
        else
            av_log(s, AV_LOG_WARNING, "Incoherent time base in packet duration calculation\n");

        /* shrink the packet itself for audio essence */

        if (st->codecpar->codec_type == AVMEDIA_TYPE_AUDIO) {

            if (st->codecpar->codec_id == AV_CODEC_ID_PCM_S24LE) {
                /* AV_CODEC_ID_PCM_S24LE is the only PCM format supported in IMF */
                /* in this case, explicitly shrink the packet */

                int bytes_per_sample = av_get_exact_bits_per_sample(st->codecpar->codec_id) >> 3;
                int64_t nbsamples = av_rescale_q(pkt->duration,
                                                 st->time_base,
                                                 av_make_q(1, st->codecpar->sample_rate));
                av_shrink_packet(pkt, nbsamples * st->codecpar->ch_layout.nb_channels * bytes_per_sample);

            } else {
                /* in all other cases, use side data to skip samples */
                int64_t skip_samples;

                ret = imf_time_to_ts(&skip_samples,
                                     av_sub_q(next_timestamp, resource->end_time),
                                     av_make_q(1, st->codecpar->sample_rate));

                if (ret || skip_samples < 0 || skip_samples > UINT32_MAX) {
                    av_log(s, AV_LOG_WARNING, "Cannot skip audio samples\n");
                } else {
                    uint8_t *side_data = av_packet_new_side_data(pkt, AV_PKT_DATA_SKIP_SAMPLES, 10);
                    if (!side_data)
                        return AVERROR(ENOMEM);

                    AV_WL32(side_data + 4, skip_samples); /* skip from end of this packet */
                    side_data[6] = 1;                     /* reason for end is convergence */
                }
            }

            next_timestamp = resource->end_time;

        } else {
            av_log(s, AV_LOG_WARNING, "Non-audio packet duration reduced\n");
        }
    }

    track->current_timestamp = next_timestamp;

    return 0;
}

static int imf_close(AVFormatContext *s)
{
    IMFContext *c = s->priv_data;

    av_log(s, AV_LOG_DEBUG, "Close IMF package\n");
    av_dict_free(&c->avio_opts);
    av_freep(&c->base_url);
    imf_asset_locator_map_deinit(&c->asset_locator_map);
    ff_imf_cpl_free(c->cpl);

    for (uint32_t i = 0; i < c->track_count; i++) {
        imf_virtual_track_playback_context_deinit(c->tracks[i]);
        av_freep(&c->tracks[i]);
    }

    av_freep(&c->tracks);

    return 0;
}

static int imf_probe(const AVProbeData *p)
{
    if (!strstr(p->buf, "<CompositionPlaylist"))
        return 0;

    /* check for a ContentTitle element without including ContentTitleText,
     * which is used by the D-Cinema CPL.
     */
    if (!strstr(p->buf, "ContentTitle>"))
        return 0;

    return AVPROBE_SCORE_MAX;
}

static int coherent_ts(int64_t ts, AVRational in_tb, AVRational out_tb)
{
    int dst_num;
    int dst_den;
    int ret;

    ret = av_reduce(&dst_num, &dst_den, ts * in_tb.num * out_tb.den,
                    in_tb.den * out_tb.num, INT64_MAX);
    if (!ret || dst_den != 1)
        return 0;

    return 1;
}

static int imf_seek(AVFormatContext *s, int stream_index, int64_t min_ts,
                    int64_t ts, int64_t max_ts, int flags)
{
    IMFContext *c = s->priv_data;
    uint32_t i;

    if (flags & (AVSEEK_FLAG_BYTE | AVSEEK_FLAG_FRAME))
        return AVERROR(ENOSYS);

    /* rescale timestamps to Composition edit units */
    if (stream_index < 0)
        ff_rescale_interval(AV_TIME_BASE_Q,
                            av_make_q(c->cpl->edit_rate.den, c->cpl->edit_rate.num),
                            &min_ts, &ts, &max_ts);
    else
        ff_rescale_interval(s->streams[stream_index]->time_base,
                            av_make_q(c->cpl->edit_rate.den, c->cpl->edit_rate.num),
                            &min_ts, &ts, &max_ts);

    /* requested timestamp bounds are too close */
    if (max_ts < min_ts)
        return -1;

    /* clamp requested timestamp to provided bounds */
    ts = FFMAX(FFMIN(ts, max_ts), min_ts);

    av_log(s, AV_LOG_DEBUG, "Seeking to Composition Playlist edit unit %" PRIi64 "\n", ts);

    /* set the dts of each stream and temporal offset of each track */
    for (i = 0; i < c->track_count; i++) {
        AVStream *st = s->streams[i];
        IMFVirtualTrackPlaybackCtx *t = c->tracks[i];
        int64_t dts;

        if (!coherent_ts(ts, av_make_q(c->cpl->edit_rate.den, c->cpl->edit_rate.num),
                         st->time_base))
            av_log(s, AV_LOG_WARNING, "Seek position is not coherent across tracks\n");

        dts = av_rescale(ts,
                         st->time_base.den * c->cpl->edit_rate.den,
                         st->time_base.num * c->cpl->edit_rate.num);

        av_log(s, AV_LOG_DEBUG, "Seeking to dts=%" PRId64 " on stream_index=%d\n",
               dts, i);

        t->current_timestamp = av_mul_q(av_make_q(dts, 1), st->time_base);
        if (t->current_resource_index >= 0) {
            avformat_close_input(&t->resources[t->current_resource_index].ctx);
            t->current_resource_index = -1;
        }
    }

    return 0;
}

static const AVOption imf_options[] = {
    {
        .name        = "assetmaps",
        .help        = "Comma-separated paths to ASSETMAP files."
                       "If not specified, the `ASSETMAP.xml` file in the same "
                       "directory as the CPL is used.",
        .offset      = offsetof(IMFContext, asset_map_paths),
        .type        = AV_OPT_TYPE_STRING,
        .default_val = {.str = NULL},
        .flags       = AV_OPT_FLAG_DECODING_PARAM,
    },
    {NULL},
};

static const AVClass imf_class = {
    .class_name = "imf",
    .item_name  = av_default_item_name,
    .option     = imf_options,
    .version    = LIBAVUTIL_VERSION_INT,
};

const AVInputFormat ff_imf_demuxer = {
    .name           = "imf",
    .long_name      = NULL_IF_CONFIG_SMALL("IMF (Interoperable Master Format)"),
    .flags          = AVFMT_EXPERIMENTAL | AVFMT_NO_BYTE_SEEK,
    .flags_internal = FF_FMT_INIT_CLEANUP,
    .priv_class     = &imf_class,
    .priv_data_size = sizeof(IMFContext),
    .read_probe     = imf_probe,
    .read_header    = imf_read_header,
    .read_packet    = imf_read_packet,
    .read_close     = imf_close,
    .read_seek2     = imf_seek,
};