matroskaenc.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 muxer
 * Copyright (c) 2007 David Conrad
 *
 * 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
 */

#include "avformat.h"
#include "md5.h"
#include "riff.h"
#include "xiph.h"
#include "matroska.h"

typedef struct ebml_master {
    offset_t        pos;                ///< absolute offset in the file where the master's elements start
    int             sizebytes;          ///< how many bytes were reserved for the size
} ebml_master;

typedef struct mkv_seekhead_entry {
    unsigned int    elementid;
    uint64_t        segmentpos;
} mkv_seekhead_entry;

typedef struct mkv_seekhead {
    offset_t                filepos;
    offset_t                segment_offset;     ///< the file offset to the beginning of the segment
    int                     reserved_size;      ///< -1 if appending to file
    int                     max_entries;
    mkv_seekhead_entry      *entries;
    int                     num_entries;
} mkv_seekhead;

typedef struct {
    uint64_t        pts;
    int             tracknum;
    offset_t        cluster_pos;        ///< file offset of the cluster containing the block
} mkv_cuepoint;

typedef struct {
    offset_t        segment_offset;
    mkv_cuepoint    *entries;
    int             num_entries;
} mkv_cues;

typedef struct MatroskaMuxContext {
    ebml_master     segment;
    offset_t        segment_offset;
    offset_t        segment_uid;
    ebml_master     cluster;
    offset_t        cluster_pos;        ///< file offset of the current cluster
    uint64_t        cluster_pts;
    offset_t        duration_offset;
    uint64_t        duration;
    mkv_seekhead    *main_seekhead;
    mkv_seekhead    *cluster_seekhead;
    mkv_cues        *cues;

    struct AVMD5    *md5_ctx;
} MatroskaMuxContext;


/** 2 bytes * 3 for EBML IDs, 3 1-byte EBML lengths, 8 bytes for 64 bit
 * offset, 4 bytes for target EBML ID */
#define MAX_SEEKENTRY_SIZE 21

/** per-cuepoint-track - 3 1-byte EBML IDs, 3 1-byte EBML sizes, 2
 * 8-byte uint max */
#define MAX_CUETRACKPOS_SIZE 22

/** per-cuepoint - 2 1-byte EBML IDs, 2 1-byte EBML sizes, 8-byte uint max */
#define MAX_CUEPOINT_SIZE(num_tracks) 12 + MAX_CUETRACKPOS_SIZE*num_tracks


static int ebml_id_size(unsigned int id)
{
    return (av_log2(id+1)-1)/7+1;
}

static void put_ebml_id(ByteIOContext *pb, unsigned int id)
{
    int i = ebml_id_size(id);
    while (i--)
        put_byte(pb, id >> (i*8));
}

/**
 * Write an EBML size meaning "unknown size".
 *
 * @param bytes The number of bytes the size should occupy (maximum: 8).
 */
static void put_ebml_size_unknown(ByteIOContext *pb, int bytes)
{
    assert(bytes <= 8);
    put_byte(pb, 0x1ff >> bytes);
    while (--bytes)
        put_byte(pb, 0xff);
}

/**
 * Calculate how many bytes are needed to represent a given number in EBML.
 */
static int ebml_num_size(uint64_t num)
{
    int bytes = 1;
    while ((num+1) >> bytes*7) bytes++;
    return bytes;
}

/**
 * Write a number in EBML variable length format.
 *
 * @param bytes The number of bytes that need to be used to write the number.
 *              If zero, any number of bytes can be used.
 */
static void put_ebml_num(ByteIOContext *pb, uint64_t num, int bytes)
{
    int i, needed_bytes = ebml_num_size(num);

    // sizes larger than this are currently undefined in EBML
    assert(num < (1ULL<<56)-1);

    if (bytes == 0)
        // don't care how many bytes are used, so use the min
        bytes = needed_bytes;
    // the bytes needed to write the given size would exceed the bytes
    // that we need to use, so write unknown size. This shouldn't happen.
    assert(bytes >= needed_bytes);

    num |= 1ULL << bytes*7;
    for (i = bytes - 1; i >= 0; i--)
        put_byte(pb, num >> i*8);
}

static void put_ebml_uint(ByteIOContext *pb, unsigned int elementid, uint64_t val)
{
    int i, bytes = 1;
    while (val >> bytes*8) bytes++;

    put_ebml_id(pb, elementid);
    put_ebml_num(pb, bytes, 0);
    for (i = bytes - 1; i >= 0; i--)
        put_byte(pb, val >> i*8);
}

static void put_ebml_float(ByteIOContext *pb, unsigned int elementid, double val)
{
    put_ebml_id(pb, elementid);
    put_ebml_num(pb, 8, 0);
    put_be64(pb, av_dbl2int(val));
}

static void put_ebml_binary(ByteIOContext *pb, unsigned int elementid,
                            const uint8_t *buf, int size)
{
    put_ebml_id(pb, elementid);
    put_ebml_num(pb, size, 0);
    put_buffer(pb, buf, size);
}

static void put_ebml_string(ByteIOContext *pb, unsigned int elementid, const char *str)
{
    put_ebml_binary(pb, elementid, str, strlen(str));
}

/**
 * Writes a void element of a given size. Useful for reserving space in
 * the file to be written to later.
 *
 * @param size The number of bytes to reserve, which must be at least 2.
 */
static void put_ebml_void(ByteIOContext *pb, uint64_t size)
{
    offset_t currentpos = url_ftell(pb);

    assert(size >= 2);

    put_ebml_id(pb, EBML_ID_VOID);
    // we need to subtract the length needed to store the size from the
    // size we need to reserve so 2 cases, we use 8 bytes to store the
    // size if possible, 1 byte otherwise
    if (size < 10)
        put_ebml_num(pb, size-1, 0);
    else
        put_ebml_num(pb, size-9, 8);
    url_fseek(pb, currentpos + size, SEEK_SET);
}

static ebml_master start_ebml_master(ByteIOContext *pb, unsigned int elementid, uint64_t expectedsize)
{
    int bytes = expectedsize ? ebml_num_size(expectedsize) : 8;
    put_ebml_id(pb, elementid);
    put_ebml_size_unknown(pb, bytes);
    return (ebml_master){ url_ftell(pb), bytes };
}

static void end_ebml_master(ByteIOContext *pb, ebml_master master)
{
    offset_t pos = url_ftell(pb);

    // leave the unknown size for masters when streaming
    if (url_is_streamed(pb))
        return;

    url_fseek(pb, master.pos - master.sizebytes, SEEK_SET);
    put_ebml_num(pb, pos - master.pos, master.sizebytes);
    url_fseek(pb, pos, SEEK_SET);
}

static void put_xiph_size(ByteIOContext *pb, int size)
{
    int i;
    for (i = 0; i < size / 255; i++)
        put_byte(pb, 255);
    put_byte(pb, size % 255);
}

/**
 * Initialize a mkv_seekhead element to be ready to index level 1 Matroska
 * elements. If a maximum number of elements is specified, enough space
 * will be reserved at the current file location to write a seek head of
 * that size.
 *
 * @param segment_offset The absolute offset to the position in the file
 *                       where the segment begins.
 * @param numelements The maximum number of elements that will be indexed
 *                    by this seek head, 0 if unlimited.
 */
static mkv_seekhead * mkv_start_seekhead(ByteIOContext *pb, offset_t segment_offset, int numelements)
{
    mkv_seekhead *new_seekhead = av_mallocz(sizeof(mkv_seekhead));
    if (new_seekhead == NULL)
        return NULL;

    new_seekhead->segment_offset = segment_offset;

    if (numelements > 0) {
        new_seekhead->filepos = url_ftell(pb);
        // 21 bytes max for a seek entry, 10 bytes max for the SeekHead ID
        // and size, and 3 bytes to guarantee that an EBML void element
        // will fit afterwards
        new_seekhead->reserved_size = numelements * MAX_SEEKENTRY_SIZE + 13;
        new_seekhead->max_entries = numelements;
        put_ebml_void(pb, new_seekhead->reserved_size);
    }
    return new_seekhead;
}

static int mkv_add_seekhead_entry(mkv_seekhead *seekhead, unsigned int elementid, uint64_t filepos)
{
    mkv_seekhead_entry *entries = seekhead->entries;

    // don't store more elements than we reserved space for
    if (seekhead->max_entries > 0 && seekhead->max_entries <= seekhead->num_entries)
        return -1;

    entries = av_realloc(entries, (seekhead->num_entries + 1) * sizeof(mkv_seekhead_entry));
    if (entries == NULL)
        return AVERROR(ENOMEM);

    entries[seekhead->num_entries  ].elementid = elementid;
    entries[seekhead->num_entries++].segmentpos = filepos - seekhead->segment_offset;

    seekhead->entries = entries;
    return 0;
}

/**
 * Write the seek head to the file and free it. If a maximum number of
 * elements was specified to mkv_start_seekhead(), the seek head will
 * be written at the location reserved for it. Otherwise, it is written
 * at the current location in the file.
 *
 * @return The file offset where the seekhead was written.
 */
static offset_t mkv_write_seekhead(ByteIOContext *pb, mkv_seekhead *seekhead)
{
    ebml_master metaseek, seekentry;
    offset_t currentpos;
    int i;

    currentpos = url_ftell(pb);

    if (seekhead->reserved_size > 0)
        url_fseek(pb, seekhead->filepos, SEEK_SET);

    metaseek = start_ebml_master(pb, MATROSKA_ID_SEEKHEAD, seekhead->reserved_size);
    for (i = 0; i < seekhead->num_entries; i++) {
        mkv_seekhead_entry *entry = &seekhead->entries[i];

        seekentry = start_ebml_master(pb, MATROSKA_ID_SEEKENTRY, MAX_SEEKENTRY_SIZE);

        put_ebml_id(pb, MATROSKA_ID_SEEKID);
        put_ebml_num(pb, ebml_id_size(entry->elementid), 0);
        put_ebml_id(pb, entry->elementid);

        put_ebml_uint(pb, MATROSKA_ID_SEEKPOSITION, entry->segmentpos);
        end_ebml_master(pb, seekentry);
    }
    end_ebml_master(pb, metaseek);

    if (seekhead->reserved_size > 0) {
        uint64_t remaining = seekhead->filepos + seekhead->reserved_size - url_ftell(pb);
        put_ebml_void(pb, remaining);
        url_fseek(pb, currentpos, SEEK_SET);

        currentpos = seekhead->filepos;
    }
    av_free(seekhead->entries);
    av_free(seekhead);

    return currentpos;
}

static mkv_cues * mkv_start_cues(offset_t segment_offset)
{
    mkv_cues *cues = av_mallocz(sizeof(mkv_cues));
    if (cues == NULL)
        return NULL;

    cues->segment_offset = segment_offset;
    return cues;
}

static int mkv_add_cuepoint(mkv_cues *cues, AVPacket *pkt, offset_t cluster_pos)
{
    mkv_cuepoint *entries = cues->entries;

    entries = av_realloc(entries, (cues->num_entries + 1) * sizeof(mkv_cuepoint));
    if (entries == NULL)
        return AVERROR(ENOMEM);

    entries[cues->num_entries  ].pts = pkt->pts;
    entries[cues->num_entries  ].tracknum = pkt->stream_index + 1;
    entries[cues->num_entries++].cluster_pos = cluster_pos - cues->segment_offset;

    cues->entries = entries;
    return 0;
}

static offset_t mkv_write_cues(ByteIOContext *pb, mkv_cues *cues, int num_tracks)
{
    ebml_master cues_element;
    offset_t currentpos;
    int i, j;

    currentpos = url_ftell(pb);
    cues_element = start_ebml_master(pb, MATROSKA_ID_CUES, 0);

    for (i = 0; i < cues->num_entries; i++) {
        ebml_master cuepoint, track_positions;
        mkv_cuepoint *entry = &cues->entries[i];
        uint64_t pts = entry->pts;

        cuepoint = start_ebml_master(pb, MATROSKA_ID_POINTENTRY, MAX_CUEPOINT_SIZE(num_tracks));
        put_ebml_uint(pb, MATROSKA_ID_CUETIME, pts);

        // put all the entries from different tracks that have the exact same
        // timestamp into the same CuePoint
        for (j = 0; j < cues->num_entries - i && entry[j].pts == pts; j++) {
            track_positions = start_ebml_master(pb, MATROSKA_ID_CUETRACKPOSITION, MAX_CUETRACKPOS_SIZE);
            put_ebml_uint(pb, MATROSKA_ID_CUETRACK          , entry[j].tracknum   );
            put_ebml_uint(pb, MATROSKA_ID_CUECLUSTERPOSITION, entry[j].cluster_pos);
            end_ebml_master(pb, track_positions);
        }
        i += j - 1;
        end_ebml_master(pb, cuepoint);
    }
    end_ebml_master(pb, cues_element);

    av_free(cues->entries);
    av_free(cues);
    return currentpos;
}

static int put_xiph_codecpriv(AVFormatContext *s, ByteIOContext *pb, AVCodecContext *codec)
{
    uint8_t *header_start[3];
    int header_len[3];
    int first_header_size;
    int j;

    if (codec->codec_id == CODEC_ID_VORBIS)
        first_header_size = 30;
    else
        first_header_size = 42;

    if (ff_split_xiph_headers(codec->extradata, codec->extradata_size,
                              first_header_size, header_start, header_len) < 0) {
        av_log(s, AV_LOG_ERROR, "Extradata corrupt.\n");
        return -1;
    }

    put_byte(pb, 2);                    // number packets - 1
    for (j = 0; j < 2; j++) {
        put_xiph_size(pb, header_len[j]);
    }
    for (j = 0; j < 3; j++)
        put_buffer(pb, header_start[j], header_len[j]);

    return 0;
}