ffmpeg 音频播放器相关

每秒理论PCM大小 = 采样率 * 声道数 * 位数/8

//44100hz 立体声 16bit
int s_time = 44100 * 2 * 16/8;

duration = pFormatCtx->duration / AV_TIME_BASE;

AVRational time_base = pFormatCtx->streams[audio_index]->time_base
double now_time = frame->pts * av_q2d(time_base);

公式：PCM实际数据大小 / 每秒理论PCM大小；
clock += buffersize / ((double)(sample_rate * 2 * 2));

AVFormatContext *pFormatCtx = NULL;
//采样率
int sample_rate =0;
//当前总时长
int duration = 0;

AVRational time_base =NULL;
//当前AvFrame时间
int now_time=0;
//当前播放时长
int clock = 0;
//上次播放时长标识
int last_time=0;

uint8_t *buffer = NULL;
int data_size=0;


//获取到 pFormatCtx
...
for(int i = 0; i < pFormatCtx->nb_streams; i++)
    {
        if(pFormatCtx->streams[i]->codecpar->codec_type == AVMEDIA_TYPE_AUDIO)//得到音频流
        {
                ...
                sample_rate = pFormatCtx->streams[i]->codecpar->sample_rate;
                duration= pFormatCtx->duration / AV_TIME_BASE;
                time_base = pFormatCtx->streams[i]->time_base;
        }
}

//解码数据  
...
    
  int nb = swr_convert(
                swr_ctx,
                &buffer,
                avFrame->nb_samples,
                (const uint8_t **) avFrame->data,
                avFrame->nb_samples);

   int out_channels = av_get_channel_layout_nb_channels(AV_CH_LAYOUT_STEREO);
   data_size = nb * out_channels * av_get_bytes_per_sample(AV_SAMPLE_FMT_S16);

    now_time = avFrame->pts * av_q2d(time_base);
    if(now_time < clock){
       now_time = clock;
    }
    clock = now_time;


//解码数据之后数据封装在 buffer，播放的时候
...

if(data_size>0){
    //size/(采样率(44100hz) * 立体声*16bit/8) 
    clock += data_size / ((double)(sample_rate * 2 * 2));
    //设置一个回掉最小相差值
    if(clock - last_tiem >= 0.1) {
        last_tiem = clock;
        //回调应用层
       callJava->onCallTimeInfo(CHILD_THREAD,clock, duration);
    } 
}

seek = true;
queue->clearAvpacket();

pthread_mutex_lock(&seek_mutex);
int64_t rel = secs * AV_TIME_BASE;
//重置内部解码器状态/刷新内部缓冲区
 avcodec_flush_buffers(avCodecContext);
//主要是这个函数
avformat_seek_file(pFormatCtx, -1, INT64_MIN, rel, INT64_MAX, 0);
pthread_mutex_unlock(&seek_mutex);
seek = false;

pthread_mutex_lock(&seek_mutex);
ret = av_read_frame(pFormatCtx, packet);
pthread_mutex_unlock(&seek_mutex);

//char*是为了都转换成字节来处理 
int WlAudio::getPCMDB(char *pcmcata, size_t pcmsize) {
    int db = 0;
    short int pervalue = 0;
    double sum = 0;
    for (int i = 0; i < pcmsize; i += 2) {
        memcpy(&pervalue, pcmcata + i, 2);
        sum += abs(pervalue);
    }
    sum = sum / (pcmsize / 2);
    if (sum > 0) {
        db = (int) 20.0 * log10(sum);
    }
    return db;
}

avcodec_flush_buffers(avCodecContext)