[FFmpeg-user] the problem: pcm data reduce after encoding and decoding using FFMPEG

[xutm]

Hi all,

    I capture audio raw PCM data with directx from microphone, write these
PCM data into 1.pcm, at the same time encode these datas using FFMPEG to
mp3 format and write into 2.mp3 files. Then i use FFMPEG to decode 2.mp3
file into raw PCM and again write into 3.pcm. the problem occurs: the size
of  file 3.pcm is far smaller than 1.pcm, and if i use CoolEdit to play the
two PCM file: 1.pcm and 3.pcm，I found if 1.pcm plays for 60 seconds, 3.pcm
only play for 34 seconds. Why this problem occurs?