Data structure analysis
VideoState
In fact, the main function is the same as the function of writing a player with 800 lines of code. It is a main encapsulation class
to save the main content of each item.
I personally think that there are several non-key common objects that need to be noticed
1 abort_request is to judge whether to exit the playback at this time, if it exits, then a series of exit operations
2 force_refresh is used when the video is playing
3 av_sync_type ffplay supports 3 synchronization methods
typedef struct VideoState {
SDL_Thread *read_tid; // 读线程句柄
AVInputFormat *iformat; // 指向demuxer
int abort_request; // =1时请求退出播放
int force_refresh; // =1时需要刷新画面，请求立即刷新画面的意思
int paused; // =1时暂停，=0时播放
int last_paused; // 暂存“暂停”/“播放”状态
int queue_attachments_req;
int seek_req; // 标识一次seek请求
int seek_flags; // seek标志，诸如AVSEEK_FLAG_BYTE等
int64_t seek_pos; // 请求seek的目标位置(当前位置+增量)
int64_t seek_rel; // 本次seek的位置增量
int read_pause_return;
AVFormatContext *ic; // iformat的上下文
int realtime; // =1为实时流
Clock audclk; // 音频时钟
Clock vidclk; // 视频时钟
Clock extclk; // 外部时钟
FrameQueue pictq; // 视频Frame队列
FrameQueue subpq; // 字幕Frame队列
FrameQueue sampq; // 采样Frame队列
Decoder auddec; // 音频解码器
Decoder viddec; // 视频解码器
Decoder subdec; // 字幕解码器
int audio_stream ; // 音频流索引
int av_sync_type; // 音视频同步类型, 默认audio master
double audio_clock; // 当前音频帧的PTS+当前帧Duration
int audio_clock_serial; // 播放序列，seek可改变此值
// 以下4个参数 非audio master同步方式使用
double audio_diff_cum; // used for AV difference average computation
double audio_diff_avg_coef;
double audio_diff_threshold;
int audio_diff_avg_count;
// end
AVStream *audio_st; // 音频流
PacketQueue audioq; // 音频packet队列
int audio_hw_buf_size; // SDL音频缓冲区的大小(字节为单位)
// 指向待播放的一帧音频数据，指向的数据区将被拷入SDL音频缓冲区。若经过重采样则指向audio_buf1，
// 否则指向frame中的音频
uint8_t *audio_buf; // 指向需要重采样的数据
uint8_t *audio_buf1; // 指向重采样后的数据
unsigned int audio_buf_size; // 待播放的一帧音频数据(audio_buf指向)的大小
unsigned int audio_buf1_size; // 申请到的音频缓冲区audio_buf1的实际尺寸
int audio_buf_index; // 更新拷贝位置 当前音频帧中已拷入SDL音频缓冲区
// 的位置索引(指向第一个待拷贝字节)
// 当前音频帧中尚未拷入SDL音频缓冲区的数据量:
// audio_buf_size = audio_buf_index + audio_write_buf_size
int audio_write_buf_size;
int audio_volume; // 音量
int muted; // =1静音，=0则正常
struct AudioParams audio_src; // 音频frame的参数
#if CONFIG_AVFILTER
struct AudioParams audio_filter_src;
#endif
struct AudioParams audio_tgt; // SDL支持的音频参数，重采样转换：audio_src->audio_tgt
struct SwrContext *swr_ctx; // 音频重采样context
int frame_drops_early; // 丢弃视频packet计数
int frame_drops_late; // 丢弃视频frame计数
enum ShowMode {
SHOW_MODE_NONE = -1, // 无显示
SHOW_MODE_VIDEO = 0, // 显示视频
SHOW_MODE_WAVES, // 显示波浪，音频
SHOW_MODE_RDFT, // 自适应滤波器
SHOW_MODE_NB
} show_mode;
// 音频波形显示使用
int16_t sample_array[SAMPLE_ARRAY_SIZE]; // 采样数组
int sample_array_index; // 采样索引
int last_i_start; // 上一开始
RDFTContext *rdft; // 自适应滤波器上下文
int rdft_bits; // 自使用比特率
FFTSample *rdft_data; // 快速傅里叶采样
int xpos;
double last_vis_time;
SDL_Texture *vis_texture; // 音频Texture
SDL_Texture *sub_texture; // 字幕显示
SDL_Texture *vid_texture; // 视频显示
int subtitle_stream; // 字幕流索引
AVStream *subtitle_st; // 字幕流
PacketQueue subtitleq; // 字幕packet队列
double frame_timer; // 记录最后一帧播放的时刻
double frame_last_returned_time; // 上一次返回时间
double frame_last_filter_delay; // 上一个过滤器延时
int video_stream; // 视频流索引
AVStream *video_st; // 视频流
PacketQueue videoq; // 视频队列
double max_frame_duration; // 一帧最大间隔. above this, we consider the jump a timestamp discontinuity
struct SwsContext *img_convert_ctx; // 视频尺寸格式变换
struct SwsContext *sub_convert_ctx; // 字幕尺寸格式变换
int eof; // 是否读取结束
char *filename; // 文件名
int width, height, xleft, ytop; // 宽、高，x起始坐标，y起始坐标
int step; // =1 步进播放模式, =0 其他模式
#if CONFIG_AVFILTER
int vfilter_idx;
AVFilterContext *in_video_filter; // the first filter in the video chain
AVFilterContext *out_video_filter; // the last filter in the video chain
AVFilterContext *in_audio_filter; // the first filter in the audio chain
AVFilterContext *out_audio_filter; // the last filter in the audio chain
AVFilterGraph *agraph; // audio filter graph
#endif
// 保留最近的相应audio、video、subtitle流的steam index
int last_video_stream, last_audio_stream, last_subtitle_stream;
SDL_cond *continue_read_thread; // 当读取数据队列满了后进入休眠时，可以通过该condition唤醒读线程
} VideoState;
MyAVPacketList
Just like the name, the decapsulated packet is saved in the form of a linked list.
It can be understood as a node of the queue. The next node can be accessed through its next field
focus! ! ! 1 serial
The concept of serial is used in many places in ffplay, which is mainly used to distinguish whether the data is continuous or not. Every time a seek is performed, the serial will be incremented by +1 to distinguish different playback sequences.
In human terms, it means that after seeking once, the items in the previous queue will of course be unusable. You should give up, give up and ask for free.
typedef struct MyAVPacketList {
AVPacket pkt; //解封装后的数据
struct MyAVPacketList *next; //下一个节点
int serial; //播放序列
} MyAVPacketList;
PacketQueue
Here, the packeQueue logic is the same as the previous 800 lines of code player logic,
saving some basic information
This packetqueue works on video, audio and subtitles at the same time.
The audio, video, and subtitle streams have their own independent PacketQueue
The serial field is also seen here. The assignment of the serial field of MyAVPacketList comes from the serial of PacketQueue, and the serial of each PacketQueue is independent.
typedef struct PacketQueue {
MyAVPacketList *first_pkt, *last_pkt; // 队首，队尾指针
int nb_packets; // 包数量，也就是队列元素数量
int size; // 队列所有元素的数据大小总和
int64_t duration; // 队列所有元素的数据播放持续时间
int abort_request; // 用户退出请求标志
int serial; // 播放序列号，和MyAVPacketList的serial作用相同，但改变的时序稍微有点不同
SDL_mutex *mutex; // 用于维持PacketQueue的多线程安全(SDL_mutex可以按pthread_mutex_t理解）
SDL_cond *cond; // 用于读、写线程相互通知(SDL_cond可以按pthread_cond_t理解)
} PacketQueue;
Functions of PacketQueue
Too much to write a new link here
Frame
The structure that actually stores decoded audio and video data is AVFrame, and AVSubtitle is used to store subtitles. This Frame is designed for audio, video, and subtitle frames, so the design of the Frame structure is similar to AVFrame, and some member variables are only for Different types work, for example, sar only works for videos. It also contains the serial playback sequence (serial is switched every seek), sar (image aspect ratio (16:9, 4:3...), the value comes from the sample_aspect_ratio variable of AVFrame.
typedef struct Frame {
AVFrame *frame; // 指向数据帧
AVSubtitle sub; // 用于字幕
int serial; // 帧序列，在seek的操作时serial会变化
double pts; // 时间戳，单位为秒
double duration; // 该帧持续时间，单位为秒
int64_t pos; // 该帧在输入文件中的字节位置
int width; // 图像宽度
int height; // 图像高读
int format; // 对于图像为(enum AVPixelFormat)，
// 对于声音则为(enum AVSampleFormat)
AVRational sar; // 图像的宽高比（16:9，4:3...），如果未知或未指定则为0/1
int uploaded; // 用来记录该帧是否已经显示过？
int flip_v; // =1则垂直翻转， = 0则正常播放
} Frame;
FrameQueue
FrameQueue is a ring buffer, a FIFO implemented with an array. The array-type ring buffer is suitable for situations where the maximum capacity of the buffer is specified in advance. Three frame_queues are created in ffplay: audio frame_queue, video frame_queue, subtitle frame_queue. Each frame_queue has a writing end and a reading end, the writing end is located in the decoding thread, and the reading end is located in the playback thread.
typedef struct FrameQueue {
Frame queue[FRAME_QUEUE_SIZE]; // FRAME_QUEUE_SIZE 最大size, 数字太大时会占用大量的内存，需要注意该值的设置
int rindex; // 读索引。待播放时读取此帧进行播放，播放后此帧成为上一帧
int windex; // 写索引
int size; // 当前总帧数
int max_size; // 可存储最大帧数
int keep_last; // = 1说明要在队列里面保持最后一帧的数据不释放，只在销毁队列的时候才将其真正释放
int rindex_shown; // 初始化为0，配合keep_last=1使用
SDL_mutex *mutex; // 互斥量
SDL_cond *cond; // 条件变量
PacketQueue *pktq; // 数据包缓冲队列
} FrameQueue;
The design of FrameQueue is as complicated as PacketQueue, and it introduces operations such as reading a node but leaving the node out of the queue, reading the next node without leaving the queue, etc. For the specific operation function of FrameQueue, see link xxx
在这里插入代码片
AudioParams
int bytes_per_sec; // 一秒时间的字节数，比如采样率48Khz，2 channel，16bit，则一秒48000*2*16/8=192000
typedef struct AudioParams {
int freq; // 采样率
int channels; // 通道数
int64_t channel_layout; // 通道布局，比如2.1声道，5.1声道等
enum AVSampleFormat fmt; // 音频采样格式，比如AV_SAMPLE_FMT_S16表示为有符号16bit深度，交错排列模式。
int frame_size; // 一个采样单元占用的字节数（比如2通道时，则左右通道各采样一次合成一个采样单元）
int bytes_per_sec; // 一秒时间的字节数，比如采样率48Khz，2 channel，16bit，则一秒48000*2*16/8=192000
} AudioParams;
struct Decoder decoder package
typedef struct Decoder {
AVPacket pkt;
PacketQueue *queue; // 数据包队列
AVCodecContext *avctx; // 解码器上下文
int pkt_serial; // 包序列
int finished; // =0，解码器处于工作状态；=非0，解码器处于空闲状态
int packet_pending; // =0，解码器处于异常状态，需要考虑重置解码器；=1，解码器处于正常状态
SDL_cond *empty_queue_cond; // 检查到packet队列空时发送 signal缓存read_thread读取数据
int64_t start_pts; // 初始化时是stream的start time
AVRational start_pts_tb; // 初始化时是stream的time_base
int64_t next_pts; // 记录最近一次解码后的frame的pts，当解出来的部分帧没有有效的pts时则使用next_pts进行推算
AVRational next_pts_tb; // next_pts的单位
SDL_Thread *decoder_tid; // 线程句柄
} Decoder;