Mp4 file audio alignment issue between 'mpeg4 codec' and 'libx264' codec and 'aac' audio_codec

[jltchiu]

Expected Behavior

I am clipping a video and then export the clip using write_videofile to write to a mp4 file.

When the codec='libx264' and audio_codec='aac' The alignment between video and audio is perfect I expect the proper alignment will also happen when codec='mpeg4 ' and audio_codec='aac'

Actual Behavior

When using codec='mpeg4 ' and audio_codec='aac', the exported mp4 file will have misalignment between video and audio. At the beginning of the exported video both seems aligned yet as the video goes the audio video become very apparently not aligned. The audio sounds the same, yet the video will be delayed comparing with audio.