matroskadec.c

ffmpeg的完整源代码和作者自己写的文档。不但有在Linux的工程哦

/*
 * Matroska file demuxer (no muxer yet)
 * Copyright (c) 2003-2004 The ffmpeg Project
 *
 * This file is part of FFmpeg.
 *
 * FFmpeg is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * FFmpeg is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with FFmpeg; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 */

/**
 * @file matroskadec.c
 * Matroska file demuxer
 * by Ronald Bultje <[e-mail]>
 * with a little help from Moritz Bunkus <[e-mail]>
 * Specs available on the matroska project page:
 * http://www.matroska.org/.
 */

#include "avformat.h"
/* For codec_get_id(). */
#include "riff.h"
#include "intfloat_readwrite.h"
#include "matroska.h"

typedef struct Track {
    MatroskaTrackType type;

    /* Unique track number and track ID. stream_index is the index that
     * the calling app uses for this track. */
    uint32_t num;
    uint32_t uid;
    int stream_index;

    char *name;
    char language[4];

    char *codec_id;
    char *codec_name;

    unsigned char *codec_priv;
    int codec_priv_size;

    uint64_t default_duration;
    MatroskaTrackFlags flags;
} MatroskaTrack;

typedef struct MatroskaVideoTrack {
    MatroskaTrack track;

    int pixel_width;
    int pixel_height;
    int display_width;
    int display_height;

    uint32_t fourcc;

    MatroskaAspectRatioMode ar_mode;
    MatroskaEyeMode eye_mode;

    //..
} MatroskaVideoTrack;

typedef struct MatroskaAudioTrack {
    MatroskaTrack track;

    int channels;
    int bitdepth;
    int internal_samplerate;
    int samplerate;
    int block_align;

    /* real audio header */
    int coded_framesize;
    int sub_packet_h;
    int frame_size;
    int sub_packet_size;
    int sub_packet_cnt;
    int pkt_cnt;
    uint8_t *buf;
    //..
} MatroskaAudioTrack;

typedef struct MatroskaSubtitleTrack {
    MatroskaTrack track;

    int ass;
    //..
} MatroskaSubtitleTrack;

#define MAX_TRACK_SIZE (FFMAX(FFMAX(sizeof(MatroskaVideoTrack), \
                                    sizeof(MatroskaAudioTrack)), \
                                    sizeof(MatroskaSubtitleTrack)))

typedef struct MatroskaLevel {
    uint64_t start;
    uint64_t length;
} MatroskaLevel;

typedef struct MatroskaDemuxIndex {
  uint64_t        pos;   /* of the corresponding *cluster*! */
  uint16_t        track; /* reference to 'num' */
  uint64_t        time;  /* in nanoseconds */
} MatroskaDemuxIndex;

typedef struct MatroskaDemuxContext {
    AVFormatContext *ctx;

    /* ebml stuff */
    int num_levels;
    MatroskaLevel levels[EBML_MAX_DEPTH];
    int level_up;

    /* matroska stuff */
    char *writing_app;
    char *muxing_app;
    int64_t created;

    /* timescale in the file */
    int64_t time_scale;

    /* num_streams is the number of streams that av_new_stream() was called
     * for ( = that are available to the calling program). */
    int num_tracks;
    int num_streams;
    MatroskaTrack *tracks[MAX_STREAMS];

    /* cache for ID peeking */
    uint32_t peek_id;

    /* byte position of the segment inside the stream */
    offset_t segment_start;

    /* The packet queue. */
    AVPacket **packets;
    int num_packets;

    /* have we already parse metadata/cues/clusters? */
    int metadata_parsed;
    int index_parsed;
    int done;

    /* The index for seeking. */
    int num_indexes;
    MatroskaDemuxIndex *index;

    /* What to skip before effectively reading a packet. */
    int skip_to_keyframe;
    AVStream *skip_to_stream;
} MatroskaDemuxContext;

/*
 * The first few functions handle EBML file parsing. The rest
 * is the document interpretation. Matroska really just is a
 * EBML file.
 */

/*
 * Return: the amount of levels in the hierarchy that the
 * current element lies higher than the previous one.
 * The opposite isn't done - that's auto-done using master
 * element reading.
 */

static int
ebml_read_element_level_up (MatroskaDemuxContext *matroska)
{
    ByteIOContext *pb = &matroska->ctx->pb;
    offset_t pos = url_ftell(pb);
    int num = 0;

    while (matroska->num_levels > 0) {
        MatroskaLevel *level = &matroska->levels[matroska->num_levels - 1];

        if (pos >= level->start + level->length) {
            matroska->num_levels--;
            num++;
        } else {
            break;
        }
    }

    return num;
}

/*
 * Read: an "EBML number", which is defined as a variable-length
 * array of bytes. The first byte indicates the length by giving a
 * number of 0-bits followed by a one. The position of the first
 * "one" bit inside the first byte indicates the length of this
 * number.
 * Returns: num. of bytes read. < 0 on error.
 */

static int
ebml_read_num (MatroskaDemuxContext *matroska,
               int                   max_size,
               uint64_t             *number)
{
    ByteIOContext *pb = &matroska->ctx->pb;
    int len_mask = 0x80, read = 1, n = 1;
    int64_t total = 0;

    /* the first byte tells us the length in bytes - get_byte() can normally
     * return 0, but since that's not a valid first ebmlID byte, we can
     * use it safely here to catch EOS. */
    if (!(total = get_byte(pb))) {
        /* we might encounter EOS here */
        if (!url_feof(pb)) {
            offset_t pos = url_ftell(pb);
            av_log(matroska->ctx, AV_LOG_ERROR,
                   "Read error at pos. %"PRIu64" (0x%"PRIx64")\n",
                   pos, pos);
        }
        return AVERROR(EIO); /* EOS or actual I/O error */
    }

    /* get the length of the EBML number */
    while (read <= max_size && !(total & len_mask)) {
        read++;
        len_mask >>= 1;
    }
    if (read > max_size) {
        offset_t pos = url_ftell(pb) - 1;
        av_log(matroska->ctx, AV_LOG_ERROR,
               "Invalid EBML number size tag 0x%02x at pos %"PRIu64" (0x%"PRIx64")\n",
               (uint8_t) total, pos, pos);
        return AVERROR_INVALIDDATA;
    }

    /* read out length */
    total &= ~len_mask;
    while (n++ < read)
        total = (total << 8) | get_byte(pb);

    *number = total;

    return read;
}

/*
 * Read: the element content data ID.
 * Return: the number of bytes read or < 0 on error.
 */

static int
ebml_read_element_id (MatroskaDemuxContext *matroska,
                      uint32_t             *id,
                      int                  *level_up)
{
    int read;
    uint64_t total;

    /* if we re-call this, use our cached ID */
    if (matroska->peek_id != 0) {
        if (level_up)
            *level_up = 0;
        *id = matroska->peek_id;
        return 0;
    }

    /* read out the "EBML number", include tag in ID */
    if ((read = ebml_read_num(matroska, 4, &total)) < 0)
        return read;
    *id = matroska->peek_id  = total | (1 << (read * 7));

    /* level tracking */
    if (level_up)
        *level_up = ebml_read_element_level_up(matroska);

    return read;
}

/*
 * Read: element content length.
 * Return: the number of bytes read or < 0 on error.
 */

static int
ebml_read_element_length (MatroskaDemuxContext *matroska,
                          uint64_t             *length)
{
    /* clear cache since we're now beyond that data point */
    matroska->peek_id = 0;

    /* read out the "EBML number", include tag in ID */
    return ebml_read_num(matroska, 8, length);
}

/*
 * Return: the ID of the next element, or 0 on error.
 * Level_up contains the amount of levels that this
 * next element lies higher than the previous one.
 */

static uint32_t
ebml_peek_id (MatroskaDemuxContext *matroska,
              int                  *level_up)
{
    uint32_t id;

    if (ebml_read_element_id(matroska, &id, level_up) < 0)
        return 0;

    return id;
}

/*
 * Seek to a given offset.
 * 0 is success, -1 is failure.
 */

static int
ebml_read_seek (MatroskaDemuxContext *matroska,
                offset_t              offset)
{
    ByteIOContext *pb = &matroska->ctx->pb;

    /* clear ID cache, if any */
    matroska->peek_id = 0;

    return (url_fseek(pb, offset, SEEK_SET) == offset) ? 0 : -1;
}

/*
 * Skip the next element.
 * 0 is success, -1 is failure.
 */

static int
ebml_read_skip (MatroskaDemuxContext *matroska)
{
    ByteIOContext *pb = &matroska->ctx->pb;
    uint32_t id;
    uint64_t length;
    int res;

    if ((res = ebml_read_element_id(matroska, &id, NULL)) < 0 ||
        (res = ebml_read_element_length(matroska, &length)) < 0)
        return res;

    url_fskip(pb, length);

    return 0;
}

/*
 * Read the next element as an unsigned int.
 * 0 is success, < 0 is failure.
 */

static int
ebml_read_uint (MatroskaDemuxContext *matroska,
                uint32_t             *id,
                uint64_t             *num)
{
    ByteIOContext *pb = &matroska->ctx->pb;
    int n = 0, size, res;
    uint64_t rlength;

    if ((res = ebml_read_element_id(matroska, id, NULL)) < 0 ||
        (res = ebml_read_element_length(matroska, &rlength)) < 0)
        return res;
    size = rlength;
    if (size < 1 || size > 8) {
        offset_t pos = url_ftell(pb);
        av_log(matroska->ctx, AV_LOG_ERROR,
               "Invalid uint element size %d at position %"PRId64" (0x%"PRIx64")\n",
                size, pos, pos);
        return AVERROR_INVALIDDATA;
    }

    /* big-endian ordening; build up number */
    *num = 0;
    while (n++ < size)
        *num = (*num << 8) | get_byte(pb);

    return 0;
}

/*
 * Read the next element as a signed int.
 * 0 is success, < 0 is failure.
 */

static int
ebml_read_sint (MatroskaDemuxContext *matroska,
                uint32_t             *id,
                int64_t              *num)
{