nginx_rtmp_module 之 ngx_rtmp_mp4_module 的mp4源码分析

一:整体代码函数预览

static ngx_int_t
ngx_rtmp_mp4_postconfiguration(ngx_conf_t *cf)
{
    ngx_rtmp_play_main_conf_t      *pmcf;
    ngx_rtmp_play_fmt_t           **pfmt, *fmt;
    pmcf = ngx_rtmp_conf_get_module_main_conf(cf, ngx_rtmp_play_module);
    pfmt = ngx_array_push(&pmcf->fmts);
    if (pfmt == NULL) {
        return NGX_ERROR;
    }
    fmt = ngx_pcalloc(cf->pool, sizeof(ngx_rtmp_play_fmt_t));
    if (fmt == NULL) {
        return NGX_ERROR;
    }
    *pfmt = fmt;
    ngx_str_set(&fmt->name, "mp4-format");
    ngx_str_set(&fmt->pfx, "mp4:");
    ngx_str_set(&fmt->sfx, ".mp4");
    fmt->init  = ngx_rtmp_mp4_init;  // 初始化
    fmt->done  = ngx_rtmp_mp4_done;  // 完成
    fmt->seek  = ngx_rtmp_mp4_seek;  // seek
    fmt->start = ngx_rtmp_mp4_start; // 开始
    fmt->stop  = ngx_rtmp_mp4_stop;  // 结束
    fmt->send  = ngx_rtmp_mp4_send;  // 发送数据
    return NGX_OK;
}

二:数据结构定义

定义

标准定义

nginx 数据结构定义

stsc 【Sample To Chunk Box】

nginx_rtmp_module 之 ngx_rtmp_mp4_module 的mp4源码分析_第1张图片

type 4 字节已经偏移过,

box_size 4 字节已经偏移过

typedef struct {

    uint32_t                            first_chunk;

    uint32_t                            samples_per_chunk;

    uint32_t                            sample_descrption_index;

} ngx_rtmp_mp4_chunk_entry_t;

typedef struct {

    uint32_t                            version_flags;

    uint32_t                            entry_count;

    ngx_rtmp_mp4_chunk_entry_t          entries[0];

} ngx_rtmp_mp4_chunks_t;

stts 【Decoding Time to Sample Box】

nginx_rtmp_module 之 ngx_rtmp_mp4_module 的mp4源码分析_第2张图片

type 4 字节已经偏移过,

box_size 4 字节已经偏移过

typedef struct {

    uint32_t                            sample_count;

    uint32_t                            sample_delta;

} ngx_rtmp_mp4_time_entry_t;

typedef struct {

    uint32_t                            version_flags;

    uint32_t                            entry_count;

    ngx_rtmp_mp4_time_entry_t           entries[0];

} ngx_rtmp_mp4_times_t;

ctts 【Composition Time to Sample Box】

nginx_rtmp_module 之 ngx_rtmp_mp4_module 的mp4源码分析_第3张图片

type 4 字节已经偏移过,

box_size 4 字节已经偏移过

typedef struct {

    uint32_t                            sample_count;

    uint32_t                            sample_offset;

} ngx_rtmp_mp4_delay_entry_t;

typedef struct {

    uint32_t                            version_flags;

    uint32_t                            entry_count;

    ngx_rtmp_mp4_delay_entry_t          entries[0];

} ngx_rtmp_mp4_delays_t;

stss 【Sync Sample Box】

nginx_rtmp_module 之 ngx_rtmp_mp4_module 的mp4源码分析_第4张图片

type 4 字节已经偏移过,

box_size 4 字节已经偏移过

typedef struct {

    uint32_t                            version_flags;

    uint32_t                            entry_count;

    uint32_t                            entries[0];

} ngx_rtmp_mp4_keys_t;

stsz 【Sample Size Boxes】

nginx_rtmp_module 之 ngx_rtmp_mp4_module 的mp4源码分析_第5张图片

type 4 字节已经偏移过,

box_size 4 字节已经偏移过

typedef struct {

    uint32_t                            version_flags; 4 字节

    uint32_t                            sample_size;

    uint32_t                            sample_count;

    uint32_t                            entries[0];

} ngx_rtmp_mp4_sizes_t;

stco 【Chunk Offset Box】

co64

nginx_rtmp_module 之 ngx_rtmp_mp4_module 的mp4源码分析_第6张图片

type 4 字节已经偏移过,

box_size 4 字节已经偏移过

typedef struct {

    uint32_t                            version_flags; 4 字节固定

    uint32_t                            entry_count;

    uint32_t                            entries[0];

} ngx_rtmp_mp4_offsets_t;

typedef struct {

    uint32_t                            version_flags;

    uint32_t                            entry_count;

    uint64_t                            entries[0];

} ngx_rtmp_mp4_offsets64_t;

三:数据结构解析

static ngx_rtmp_mp4_box_t                       ngx_rtmp_mp4_boxes[] = {
    { ngx_rtmp_mp4_make_tag('t','r','a','k'),   ngx_rtmp_mp4_parse_trak   },
    { ngx_rtmp_mp4_make_tag('m','d','i','a'),   ngx_rtmp_mp4_parse        },
    { ngx_rtmp_mp4_make_tag('m','d','h','d'),   ngx_rtmp_mp4_parse_mdhd   },
    { ngx_rtmp_mp4_make_tag('h','d','l','r'),   ngx_rtmp_mp4_parse_hdlr   },
    { ngx_rtmp_mp4_make_tag('m','i','n','f'),   ngx_rtmp_mp4_parse        },
    { ngx_rtmp_mp4_make_tag('s','t','b','l'),   ngx_rtmp_mp4_parse        },
    { ngx_rtmp_mp4_make_tag('s','t','s','d'),   ngx_rtmp_mp4_parse_stsd   },
    { ngx_rtmp_mp4_make_tag('s','t','s','c'),   ngx_rtmp_mp4_parse_stsc   },  // 记录了每个chunk中包含多少sample
    { ngx_rtmp_mp4_make_tag('s','t','t','s'),   ngx_rtmp_mp4_parse_stts   },  // sample 解码时间的压缩表
    { ngx_rtmp_mp4_make_tag('c','t','t','s'),   ngx_rtmp_mp4_parse_ctts   },  // 帧解码到渲染的时间差值,通常用在B帧的场景,sample的CTS与DTS的时间差的压缩表
    { ngx_rtmp_mp4_make_tag('s','t','s','s'),   ngx_rtmp_mp4_parse_stss   },  // 关键帧映射表
    { ngx_rtmp_mp4_make_tag('s','t','s','z'),   ngx_rtmp_mp4_parse_stsz   },  // 每帧数据的大小
    { ngx_rtmp_mp4_make_tag('s','t','z','2'),   ngx_rtmp_mp4_parse_stz2   },
    { ngx_rtmp_mp4_make_tag('s','t','c','o'),   ngx_rtmp_mp4_parse_stco   },  // 记录了chunk对应的offset
    { ngx_rtmp_mp4_make_tag('c','o','6','4'),   ngx_rtmp_mp4_parse_co64   },
    { ngx_rtmp_mp4_make_tag('a','v','c','1'),   ngx_rtmp_mp4_parse_avc1   },
    { ngx_rtmp_mp4_make_tag('a','v','c','C'),   ngx_rtmp_mp4_parse_avcC   },   // sps pps 解析
    { ngx_rtmp_mp4_make_tag('m','p','4','a'),   ngx_rtmp_mp4_parse_mp4a   },
    { ngx_rtmp_mp4_make_tag('m','p','4','v'),   ngx_rtmp_mp4_parse_mp4v   },
    { ngx_rtmp_mp4_make_tag('e','s','d','s'),   ngx_rtmp_mp4_parse_esds   },
    { ngx_rtmp_mp4_make_tag('.','m','p','3'),   ngx_rtmp_mp4_parse_mp3    },
    { ngx_rtmp_mp4_make_tag('n','m','o','s'),   ngx_rtmp_mp4_parse_nmos   },
    { ngx_rtmp_mp4_make_tag('s','p','e','x'),   ngx_rtmp_mp4_parse_spex   },
    { ngx_rtmp_mp4_make_tag('w','a','v','e'),   ngx_rtmp_mp4_parse        }
};

ngx_rtmp_mp4_parse_stsc   记录了每个chunk中包含多少sample

nginx_rtmp_module 之 ngx_rtmp_mp4_module 的mp4源码分析_第7张图片

上图数据解析

00 00 00 28(size) --> 40 字节总大小包含的自己在内的所有数据:

00 00 00 28(size) 73 74 73 63(stsc) 00 00 00 00(version_flags) 00 00 00 02(entry_count) 00 00 00 01(first_chunk) 00 00 00 02(samples_per_chunk) 00 00 00 01(sample_descrption_index) 00 00 00 02(first_chunk) 00 00 00 01(samples_per_chunk) 00 00 00 01(sample_descrption_index)

static ngx_int_t
ngx_rtmp_mp4_parse_stsc(ngx_rtmp_session_t *s, u_char *pos, u_char *last)
{
    ngx_rtmp_mp4_ctx_t         *ctx;
    ngx_rtmp_mp4_track_t       *t;
    ctx = ngx_rtmp_get_module_ctx(s, ngx_rtmp_mp4_module);
    t = ctx->track;
    if (t == NULL) {
        return NGX_OK;
    }
    t->chunks = (ngx_rtmp_mp4_chunks_t *) pos;  // 内存数据上面的解析
    if (pos + sizeof(*t->chunks) + ngx_rtmp_r32(t->chunks->entry_count) *
                                   sizeof(t->chunks->entries[0])
        <= last)// 内存越界判断
    {
        return NGX_OK;
    }
    t->chunks = NULL;
    return NGX_ERROR;
}

ngx_rtmp_mp4_parse_stco  记录了chunk对应的offset

nginx_rtmp_module 之 ngx_rtmp_mp4_module 的mp4源码分析_第8张图片

00 00 03 D4(980 长度) 73 74 63 6F (stco)00 00 00 00(version_flags) 00 00 00 F1( entry_count 241 ) 00 00 00 30( entrie) 00 00 10 4D ( entrie)00 00 20 1C( entrie) 00 00 29 38( entrie) 00 00 49 2D( entrie) 00 00 70 C9( entrie) 00 00 B1 C1 ( entrie) ...............

static ngx_int_t
ngx_rtmp_mp4_parse_stco(ngx_rtmp_session_t *s, u_char *pos, u_char *last)
{
    ngx_rtmp_mp4_ctx_t         *ctx;
    ngx_rtmp_mp4_track_t       *t;
    ctx = ngx_rtmp_get_module_ctx(s, ngx_rtmp_mp4_module);
    t = ctx->track;
    if (t == NULL) {
        return NGX_OK;
    }
    t->offsets = (ngx_rtmp_mp4_offsets_t *) pos; // 数据结构的赋值
    if (pos + sizeof(*t->offsets) + ngx_rtmp_r32(t->offsets->entry_count) *
                                    sizeof(t->offsets->entries[0])
        <= last) // 内存越界判断
    {
        return NGX_OK;
    }
    t->offsets = NULL;
    return NGX_ERROR;
}

其他数据结构的解析与上面的流程基本一样

四:数据处理流程

nginx_rtmp_module 之 ngx_rtmp_mp4_module 的mp4源码分析_第9张图片

五:play 流程代码分析

ffplay -analyzeduration 1000000 "rtmp://10.90.103.5/vod/0001.mp4

nginx_rtmp_module 之 ngx_rtmp_mp4_module 的mp4源码分析_第10张图片

nginx_rtmp_module 之 ngx_rtmp_mp4_module 的mp4源码分析_第11张图片

1> ngx_rtmp_mp4_init 初始化变量解析 mp4 moov box 的数据结构

2> ngx_rtmp_mp4_seek (ngx_rtmp_session_t *s, ngx_file_t *f, ngx_uint_t timestamp), timestamp = 0 ,seek 时间戳为零标识从头开始播放。ngx_rtmp_mp4_seek_track 有两个轨道,音频轨和视频轨,分别进行seek

static ngx_int_t
ngx_rtmp_mp4_seek_track(ngx_rtmp_session_t *s, ngx_rtmp_mp4_track_t *t,
                        ngx_int_t timestamp)
{
    ngx_rtmp_mp4_cursor_t          *cr;
    cr = &t->cursor;
    ngx_memzero(cr, sizeof(*cr));
    if (ngx_rtmp_mp4_seek_time(s, t, ngx_rtmp_mp4_from_rtmp_timestamp(  // ngx_rtmp_mp4_from_rtmp_timestamp 时间戳的
                          t, timestamp)) != NGX_OK ||
        ngx_rtmp_mp4_seek_key(s, t)   != NGX_OK ||
        ngx_rtmp_mp4_seek_chunk(s, t) != NGX_OK ||
        ngx_rtmp_mp4_seek_size(s, t)  != NGX_OK ||
        ngx_rtmp_mp4_seek_delay(s, t) != NGX_OK)
    {
        return NGX_ERROR;
    }
    cr->valid = 1;
    return NGX_OK;
} 

// 时间戳的转换函数,mp4 文件到rtmp
// rtmp_mp4 存放的是timescale 时间戳 通常是 12288
// rtmp 时间刻度通常是 1000 
static ngx_inline uint32_t
ngx_rtmp_mp4_to_rtmp_timestamp(ngx_rtmp_mp4_track_t *t, uint64_t ts) // 给定一个时间值 从rtmp_mp4 12288 刻度转换到 1000
{
    return (uint32_t) (ts * 1000 / t->time_scale); 
}
static ngx_inline uint32_t
ngx_rtmp_mp4_from_rtmp_timestamp(ngx_rtmp_mp4_track_t *t, uint32_t ts) // 给定一个时间值 从rtmp 1000 刻度转换到12288
{
    return (uint64_t) ts * t->time_scale / 1000;
}

ngx_rtmp_mp4_seek_time :

stts:

typedef struct {

    uint32_t                            sample_count;

    uint32_t                            sample_delta;

} ngx_rtmp_mp4_time_entry_t;

typedef struct {

    uint32_t                            version_flags;

    uint32_t                            entry_count;

    ngx_rtmp_mp4_time_entry_t           entries[0];

} ngx_rtmp_mp4_times_t;

nginx_rtmp_module 之 ngx_rtmp_mp4_module 的mp4源码分析_第12张图片 nginx_rtmp_module 之 ngx_rtmp_mp4_module 的mp4源码分析_第13张图片
static ngx_int_t
ngx_rtmp_mp4_seek_time(ngx_rtmp_session_t *s, ngx_rtmp_mp4_track_t *t,
                       uint32_t timestamp)
{
    ngx_rtmp_mp4_cursor_t      *cr;
    ngx_rtmp_mp4_time_entry_t  *te;
    uint32_t                    dt;
    if (t->times == NULL) {
        return NGX_ERROR;
    }
    cr = &t->cursor; // 对应音频或者视频轨道的游标器
    te = t->times->entries; // times --> ngx_rtmp_mp4_times_t
    // sample_counts	6,1,5,1,5,1,1,1,1,1
    // sample_deltas	1024,3040,1024,3088,1024,1008,1024,1032,1024,1048     
    // 整个循环就是处理,遍历sample_counts个sample_deltas值与 参数 timestamp比大小. 1. 小于记录 cr->timestamp += dt,
    while (cr->time_pos < ngx_rtmp_r32(t->times->entry_count)) {
        dt = ngx_rtmp_r32(te->sample_delta) * ngx_rtmp_r32(te->sample_count); // 242 * 1024 = 22757376 
        // cr->timestamp + dt >= timestamp ,在这个范围说明找到
        if (cr->timestamp + dt >= timestamp) {
            if (te->sample_delta == 0) {
                return NGX_ERROR;
            }
            cr->time_count = (timestamp - cr->timestamp) /
                             ngx_rtmp_r32(te->sample_delta);                   // sample_delta 相同,cr->time_count 等于当前时间戳距离这个entry开始时间错的插值,的第几个delta
            cr->timestamp += ngx_rtmp_r32(te->sample_delta) * cr->time_count;  // seek 的时间戳,就是把 cr->timestamp 修改当前的时间戳
            cr->pos += cr->time_count;                                         // 记录当前seek 对应时间戳具体的位置
            break;
        }
        // 没找到,
        cr->timestamp += dt;                       // 记录值进行累加,访问下一个
        cr->pos += ngx_rtmp_r32(te->sample_count); // 记录pos 的位置
        cr->time_pos++;                            // 记录已经访问第几个entry
        te++;                                      // te++ 下一个entry
    }
    if (cr->time_pos >= ngx_rtmp_r32(t->times->entry_count)) {
        return  NGX_ERROR;
    }
    return NGX_OK;
}

ngx_rtmp_mp4_seek_key

stss

typedef struct {

    uint32_t                            version_flags;

    uint32_t                            entry_count; // 个数

    uint32_t                            entries[0]; // pos

} ngx_rtmp_mp4_keys_t;

nginx_rtmp_module 之 ngx_rtmp_mp4_module 的mp4源码分析_第14张图片
static ngx_int_t
ngx_rtmp_mp4_seek_key(ngx_rtmp_session_t *s, ngx_rtmp_mp4_track_t *t)
{
    ngx_rtmp_mp4_cursor_t      *cr;
    uint32_t                   *ke;
    ngx_int_t                   dpos;
    cr = &t->cursor;       // 对应音频或者视频轨道的游标器
    if (t->keys == NULL) {
        return NGX_OK;
    }
    // cr->key_pos 初始值为0 ,t->keys->entry_count 关键帧的个数
    while (cr->key_pos < ngx_rtmp_r32(t->keys->entry_count)) {
        // 遍历每一个entry得到帧号,与当前pos位置进行对比,找到当前位置的下一个关键帧
        if (ngx_rtmp_r32(t->keys->entries[cr->key_pos]) > cr->pos) {    // cr->pos 上面seek 后具体位置
            break;
        }
        cr->key_pos++;
    }
    if (cr->key_pos >= ngx_rtmp_r32(t->keys->entry_count)) {
        return NGX_OK;
    }
    ke = &t->keys->entries[cr->key_pos];                                // 
    dpos = ngx_rtmp_r32(*ke) - cr->pos - 1;                             // 计算距离下一个关键帧的差值
    cr->key = 1;
    /* TODO: range version needed */
    for (; dpos > 0; --dpos) {
        ngx_rtmp_mp4_next_time(s, t);
    }
    return NGX_OK;
}

ngx_rtmp_mp4_seek_chunk

stsc

typedef struct {

    uint32_t                            first_chunk;

    uint32_t                            samples_per_chunk;

    uint32_t                            sample_descrption_index;

} ngx_rtmp_mp4_chunk_entry_t;

typedef struct {

    uint32_t                            version_flags;

    uint32_t                            entry_count;

    ngx_rtmp_mp4_chunk_entry_t          entries[0];

} ngx_rtmp_mp4_chunks_t;

nginx_rtmp_module 之 ngx_rtmp_mp4_module 的mp4源码分析_第15张图片 nginx_rtmp_module 之 ngx_rtmp_mp4_module 的mp4源码分析_第16张图片
static ngx_int_t
ngx_rtmp_mp4_seek_chunk(ngx_rtmp_session_t *s, ngx_rtmp_mp4_track_t *t)
{
    ngx_rtmp_mp4_cursor_t          *cr;
    ngx_rtmp_mp4_chunk_entry_t     *ce, *nce;
    ngx_uint_t                      pos, dpos, dchunk;
    cr = &t->cursor;                                              // 对应音频或者视频轨道的游标器
    if (t->chunks == NULL || t->chunks->entry_count == 0) {
        cr->chunk = 1;
        return NGX_OK;
    }
    ce = t->chunks->entries;                                      // entry 实体结构  
    pos = 0;
    // cr->chunk_pos 初始值是0 
    while (cr->chunk_pos + 1 < ngx_rtmp_r32(t->chunks->entry_count)) {
        nce = ce + 1;                                             // 下一个entry
        dpos = (ngx_rtmp_r32(nce->first_chunk) -
                ngx_rtmp_r32(ce->first_chunk)) *
                ngx_rtmp_r32(ce->samples_per_chunk);              // 距离下一个chunk总共有多少点,(2-1) * 2 = 2 帧
        if (pos + dpos > cr->pos) {                               // 判断当前位置是不是在这个chunk 中
            break;
        }
        pos += dpos;                                              // pos 从头遍历累加 
        ce++;                                                     // 访问下一个entry
        cr->chunk_pos++;                                          // chunk_pos ++,记录游标当前在第几个chunk位置 
    }
    if (ce->samples_per_chunk == 0) {
        return NGX_ERROR;
    }
    dchunk = (cr->pos - pos) / ngx_rtmp_r32(ce->samples_per_chunk); // seek 之后的当前pos 位置,与找到chunk的pos差值,相同连续的chunk 可能不记录写进去。
    // 比如:  first_chunk   1,2,3,4,5,6,12,13
    //  samples_per_chunk   1,4,2,4,2,4,3, 4      ---> 1 + 4 + 2 + 4 + 2 + 4 = 17 , 18 --> 38 之间都是; 这个时候会有一个 dchunk差值
    
    cr->chunk = ngx_rtmp_r32(ce->first_chunk) + dchunk;             // 得到当前游标chunk的值,真实对应chunk 位置。
    cr->chunk_pos = (ngx_uint_t) (ce - t->chunks->entries);         // cr->chunk_pos 记录的是存储的真实解析位置
    cr->chunk_count = (ngx_uint_t) (cr->pos - pos - dchunk *
                                    ngx_rtmp_r32(ce->samples_per_chunk)); // 剩余是 chunk 偏移的变量帧
    return ngx_rtmp_mp4_update_offset(s, t);
}

static ngx_int_t
ngx_rtmp_mp4_update_offset(ngx_rtmp_session_t *s, ngx_rtmp_mp4_track_t *t)
{
    ngx_rtmp_mp4_cursor_t          *cr;
    ngx_uint_t                      chunk;
    cr = &t->cursor;
    if (cr->chunk < 1) {
        return NGX_ERROR;
    }
    chunk = cr->chunk - 1; // 数组访问 -1  
    if (t->offsets) {
        if (chunk >= ngx_rtmp_r32(t->offsets->entry_count)) {
            return NGX_ERROR;
        }
        cr->offset = (off_t) ngx_rtmp_r32(t->offsets->entries[chunk]); // 取出第几个chunk偏移大小进行赋值
        cr->size = 0;
        return NGX_OK;
    }
    if (t->offsets64) {
        if (chunk >= ngx_rtmp_r32(t->offsets64->entry_count)) {
            return NGX_ERROR;
        }
        cr->offset = (off_t) ngx_rtmp_r64(t->offsets64->entries[chunk]);
        cr->size = 0;
        return NGX_OK;
    }
    return NGX_ERROR;
}

ngx_rtmp_mp4_seek_size

stsz

typedef struct {

    uint32_t                            version_flags; 4 字节

    uint32_t                            sample_size;

    uint32_t                            sample_count;

    uint32_t                            entries[0];

} ngx_rtmp_mp4_sizes_t;

nginx_rtmp_module 之 ngx_rtmp_mp4_module 的mp4源码分析_第17张图片
static ngx_int_t
ngx_rtmp_mp4_seek_size(ngx_rtmp_session_t *s, ngx_rtmp_mp4_track_t *t)
{
    ngx_rtmp_mp4_cursor_t      *cr;
    ngx_uint_t                  pos;
    cr = &t->cursor;                                             // 当前游标
    if (cr->chunk_count > cr->pos) {                             // 》 ??
        return NGX_ERROR;
    }
    if (t->sizes) {
        if (t->sizes->sample_size) {
            cr->size = ngx_rtmp_r32(t->sizes->sample_size);
            cr->offset += cr->size * cr->chunk_count;
            return NGX_OK;
        }
        if (cr->pos >= ngx_rtmp_r32(t->sizes->sample_count)) {
            return NGX_ERROR;
        }
        for (pos = 1; pos <= cr->chunk_count; ++pos) {           // chunk_count ??
            cr->offset += ngx_rtmp_r32(t->sizes->entries[cr->pos - pos]); 
        }
        cr->size_pos = cr->pos;                                   // seek 时间戳当前pos
        cr->size = ngx_rtmp_r32(t->sizes->entries[cr->size_pos]); // 获取当前pos对应帧数据大小
        return NGX_OK;
    }
    if (t->sizes2) {
        if (cr->size_pos >= ngx_rtmp_r32(t->sizes2->sample_count)) {
            return NGX_ERROR;
        }
        cr->size_pos = cr->pos;
        return NGX_OK;
    }
    return NGX_ERROR;
}

ngx_rtmp_mp4_seek_delay

ctts

typedef struct {

    uint32_t                            sample_count;

    uint32_t                            sample_offset;

} ngx_rtmp_mp4_delay_entry_t;

typedef struct {

    uint32_t                            version_flags;

    uint32_t                            entry_count;

    ngx_rtmp_mp4_delay_entry_t          entries[0];

} ngx_rtmp_mp4_delays_t;

nginx_rtmp_module 之 ngx_rtmp_mp4_module 的mp4源码分析_第18张图片
static ngx_int_t
ngx_rtmp_mp4_seek_delay(ngx_rtmp_session_t *s, ngx_rtmp_mp4_track_t *t)
{
    ngx_rtmp_mp4_cursor_t      *cr;
    ngx_rtmp_mp4_delay_entry_t *de;
    uint32_t                    pos, dpos;
    cr = &t->cursor;
    if (t->delays == NULL) {
        return NGX_OK;
    }
    pos = 0;
    de = t->delays->entries;
    while (cr->delay_pos < ngx_rtmp_r32(t->delays->entry_count)) { // 遍历所有entry
        dpos = ngx_rtmp_r32(de->sample_count);                     // 2 表示:sample的个数
        if (pos + dpos > cr->pos) {                                // 0 + 2 > 0 , 当前pos 帧在其中
            cr->delay_count = cr->pos - pos;                       // 差值 count
            cr->delay = ngx_rtmp_r32(de->sample_offset);           // 偏移大小
            break;
        }
        cr->delay_pos++; // 记录entry访问的位置
        pos += dpos;     // pos 累加计数
        de++;            // 下一个entry
    }
    if (cr->delay_pos >= ngx_rtmp_r32(t->delays->entry_count)) {
        return NGX_OK;
    }
    return NGX_OK;
}

3> ngx_rtmp_mp4_next play 播放一直取下一帧数据

static ngx_int_t
ngx_rtmp_mp4_next(ngx_rtmp_session_t *s, ngx_rtmp_mp4_track_t *t)
{
    if (ngx_rtmp_mp4_next_time(s, t)  != NGX_OK ||
        ngx_rtmp_mp4_next_key(s, t)   != NGX_OK ||
        ngx_rtmp_mp4_next_chunk(s, t) != NGX_OK ||
        ngx_rtmp_mp4_next_size(s, t)  != NGX_OK ||
        ngx_rtmp_mp4_next_delay(s, t) != NGX_OK)
    {
        t->cursor.valid = 0;
        return NGX_ERROR;
    }
    t->cursor.valid = 1;
    return NGX_OK;
}

六:代码调试

使用进行查看变量的值: ngx_rtmp_r32(t->delays->entry_count)

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