音频采样率，时间戳分析

1. FFmpeg一个音频帧信息：

2. pkt duration

pkt_duration = nb_samples / sample_rate

sample_rate = 48000
nb_samples = 1024
pkt_duration = 1024 / 48000 = 0.021333

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3. 显示时间与pts

presentation_time = pts / sample_rate

pts = 6384
sample_rate = 48000
presentation_time = 6384 / 48000 = 0.133

4. 音频时间戳的特点

（1）pts = n * 1024
（2）nb_samples = 1024
（3）pts = last_pts + nb_samples