implement a streaming media player by j2me   

1、does the jar packet can use in a j2me environment ? I can create a player to show a mp4 file using the IBMtoolkitForMpeg4SDK.JAR, but when i use them in j2me,the eclipse throw a mistake such as "Uncaught exception java/lang/NoClassDefFoundError: player/PlayerControl."

If you only want the player capability you can use the smaller IBMPlayerForMpeg4SDK.jar. The one you are using also includes the authoring function. You can certainly use the player in J2ME CDC Personal Profile environment. It sounds as though the jar file is not in the classpath since it can't find that class.

2、the paper declare it can use the Class in the sdk avgen packet to get a frame,decode a frame etc.but i can not find such Class ,except a avgen Class with only a run() mathod in the IBMtoolkitForMpeg4SDK.JAR.

I am not sure what paper you refer, could this be with the other MPEG-4 technology that is here on alphaworks, i.e. MPEG-4 for JMF? In any case the Toolkit has no API to provide such function as you have seen.

3、i have read steve'posts,does it mean that,if i receiving a media streaming,as the tool don't support audio in CDC,i need to use the tool(if it can) to decode the video part and also need to write a audio-decoder by myself to decode the audio part?

While the toolkit can decode audio in a CDC environment there is no player there for the toolkit to output/play the audio. In the early VMs it used some internal classes sun.audio to play audio, nowadays it will use javax.sound and only fall back and try sun.audio if it can't find javax.sound support. In J2ME there is neither player and hence it doesn't play audio. My suggestion in a prior post, of separately decoding/playing audio, was the only way I could thing to get audio for the demo that was required. It can be quite a bit of work obviously and then will have potential issues with synchronization.

Steve