问题:

I am going to make a PTT project on Android. Could you tell me how deep Android supports Voice and Multimedia API (such as RTP,RTSP,VoIP) for developers?

回答1:

MediaPlayer supports playing rtsp://.. URLs. Audio and Video are supported. Check media format support to see which codecs are supported.

MediaPlayer internally automatically handles RTSP and RTP, so there is not much you need to handle. OTOH it does not give any low-level control over this process.

About VoIP: Android only consumes RTSP/RTP streams, but does not create/publish them. So this is one-way only.

Android 2.3 (Gingerbread) is said to have support for SIP-based VoIP.

回答2:

Use AudioTrack\AudioRecord APIs for streaming audio recording and playback. They allow you to deal with raw audio frames.

RTP packets are pretty straightforward - it's just a packet that contains some minimal header data and a raw audio frame. It is easy to implement - check out SipDroid for a reference implementation of RTP packets.