ffmpeg中MP4的解复用过程

主要流程

1.在s->io_open()中创建了URLContext和它的prot成员(URLProtcol)。其中URLProtcol对应的协议为file:

MP4解复用00.PNG

其中MP4的URLProtcol为：

const URLProtocol ff_file_protocol = {
    .name                = "file",
    .url_open            = file_open,
    .url_read            = file_read,
    .url_write           = file_write,
    .url_seek            = file_seek,
    .url_close           = file_close,
    .url_get_file_handle = file_get_handle,
    .url_check           = file_check,
    .url_delete          = file_delete,
    .url_move            = file_move,
    .priv_data_size      = sizeof(FileContext),
    .priv_data_class     = &file_class,
    .url_open_dir        = file_open_dir,
    .url_read_dir        = file_read_dir,
    .url_close_dir       = file_close_dir,
    .default_whitelist   = "file,crypto"
};

在libformate/file.c文件中。

2.在av_probe_input_buffer2()中判断出AVInputFormat：

av_probe_input_buffer2().PNG

3.av_probe_input_format3()函数：

这里写图片描述

4.mp4对应的read_probe为mov_probe()，在mov.c文件中;

MP4对应的AVFormatContext

AVInputFormat ff_mov_demuxer = {
    .name           = "mov,mp4,m4a,3gp,3g2,mj2",
    .long_name      = NULL_IF_CONFIG_SMALL("QuickTime / MOV"),
    .priv_class     = &mov_class,
    .priv_data_size = sizeof(MOVContext),
    .extensions     = "mov,mp4,m4a,3gp,3g2,mj2",
    .read_probe     = mov_probe,
    .read_header    = mov_read_header,
    .read_packet    = mov_read_packet,
    .read_close     = mov_read_close,
    .read_seek      = mov_read_seek,
    .flags          = AVFMT_NO_BYTE_SEEK,
};

4.在s->iformat->read_header(s)，实际为mov_read_header()中，创建MP4文件的AVStream：