对文件大小的贡献，按重要性的顺序，依次是视频比特率、音频采样频率、音频比特率，然后是帧速。
Contributing to the file size, in order of importance, are the parameters that set the video bit rate, audio sample frequency, audio bit rate, then frame size.
注意，对MP3的支持仅限于以44.1 KHz、22 KHz, 11 KHz, 8 KHz和5.5 khz频率采样的音频文件。
Note that support for MP3 is limited to audio files sampled at 44.1 KHz, 22 KHz, 11 KHz, 8 KHz, and 5.5 KHz.
它使用值1作为声道的默认值，使用值44100 Hz作为默认的音频采样频率。
It USES the value of 1 as the default for the audio channels and the value of 44100 Hz as the default audio sampling frequency.
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