[FFmpeg-user] Issue when encoding a MP4 video

[Léonce ANDRIANJAFY]

Hello,
I try to convert a MP4 video with a libspeex audio codec to an another one
but with an aac audio codec. In other words, I would like to only get the
audio stream re-encoded

I launch the command below:
*ffmpeg -i 1281904405.mp4 -vcodec copy -acodec libvo_aacenc -ab 32k
1281904405_aac.mp4*

But still I got this error:
*[mp4 @ 0x646be0] Application provided invalid, non monotonically
increasing dts to muxer in stream 0: 16 >= 16*
*av_interleaved_write_frame(): Invalid argument*

Could you help me please?

Regards

-- 

*Léonce ANDRIANJAFY*