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153 lines
No EOL
4.8 KiB
Text
153 lines
No EOL
4.8 KiB
Text
/**
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* @defgroup howto0_samplegraph Howto 1: build a sample audio graph.
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* @ingroup mediastreamer2
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<H1>Initialize mediastreamer2</H1>
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When using mediastreamer2, your first task is to initialize the
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library:
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<PRE>
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##include <mediastreamer2/mscommon.h>
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int i;
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i=ms_init();
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if (i!=0)
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return -1;
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</PRE>
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Mediastreamer2 provides internal components which are called filters. Those
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filters must be linked together so that OUTPUT from one filter is sent to
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INPUT of the other filters.
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Usually, filters are used for processing audio or video data. They could
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capture data, play/draw data, encode/decode data, mix data (conference),
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transform data (echo canceller). One of the most important filter is the
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RTP filters that are able to send and receive RTP data.
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<H1>Graph sample</H1>
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If you are using mediastreamer2, you probably want to do Voice Over IP
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and get a graph providing a 2 way communication. This 2 graphs are very
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simple:
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This first graph shows the filters needed to capture data from a sound
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card, encode them and send it through an RTP session.
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<PRE>
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AUDIO -> ENCODER -> RTP
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CAPTURE -> -> SENDER
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</PRE>
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This second graph shows the filters needed to receive data from an RTP
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session decode it and send it to the playback device.
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<PRE>
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RTP -> DECODER -> DTMF -> AUDIO
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RECEIVER -> -> GENERATION -> PLAYBACK
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</PRE>
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<H1>Code to initiate the filters of the Graph sample</H1>
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Note that the NULL/error checks are not done for better reading.
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To build the graph, you'll need some information: you need to
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select the sound card and of course have an RTP session created
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with oRTP.
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<PRE>
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MSSndCard *sndcard;
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sndcard=ms_snd_card_manager_get_default_card(ms_snd_card_manager_get());
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/* audio capture filter */
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MSFilter *soundread=ms_snd_card_create_reader(captcard);
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MSFilter *soundwrite=ms_snd_card_create_writer(playcard);
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MSFilter *encoder=ms_filter_create_encoder("PCMU");
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MSFilter *decoder=ms_filter_create_decoder("PCMU");
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MSFilter *rtpsend=ms_filter_new(MS_RTP_SEND_ID);
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MSFilter *rtprecv=ms_filter_new(MS_RTP_RECV_ID);
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RtpSession *rtp_session = *** your_ortp_session *** ;
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ms_filter_call_method(rtpsend,MS_RTP_SEND_SET_SESSION,rtp_session);
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ms_filter_call_method(rtprecv,MS_RTP_RECV_SET_SESSION,rtp_session);
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MSFilter *dtmfgen=ms_filter_new(MS_DTMF_GEN_ID);
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</PRE>
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In most cases, the above graph is not enough: you'll need to configure
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filter's options. As an example, you need to set sampling rate of sound
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cards' filters:
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<PRE>
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int sr = 8000;
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int chan=1;
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ms_filter_call_method(soundread,MS_FILTER_SET_SAMPLE_RATE,&sr);
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ms_filter_call_method(soundwrite,MS_FILTER_SET_SAMPLE_RATE,&sr);
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ms_filter_call_method(stream->encoder,MS_FILTER_SET_SAMPLE_RATE,&sr);
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ms_filter_call_method(stream->decoder,MS_FILTER_SET_SAMPLE_RATE,&sr);
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ms_filter_call_method(soundwrite,MS_FILTER_SET_NCHANNELS, &chan);
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/* if you have some fmtp parameters (from SDP for example!)
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char *fmtp1 = ** get your fmtp line **;
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char *fmtp2 = ** get your fmtp line **;
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ms_filter_call_method(stream->encoder,MS_FILTER_ADD_FMTP, (void*)fmtp1);
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ms_filter_call_method(stream->decoder,MS_FILTER_ADD_FMTP,(void*)fmtp2);
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</PRE>
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<H1>Code to link the filters and run the graph sample</H1>
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<PRE>
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ms_filter_link(stream->soundread,0,stream->encoder,0);
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ms_filter_link(stream->encoder,0,stream->rtpsend,0);
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ms_filter_link(stream->rtprecv,0,stream->decoder,0);
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ms_filter_link(stream->decoder,0,stream->dtmfgen,0);
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ms_filter_link(stream->dtmfgen,0,stream->soundwrite,0);
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</PRE>
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Then you need to 'attach' the filters to a ticker. A ticker is a graph
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manager responsible for running filters.
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In the above case, there is 2 independant graph within the ticker: you
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need to attach the first element of each graph (the one that does not
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contains any INPUT pins)
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<PRE>
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/* create ticker */
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MSTicker *ticker=ms_ticker_new();
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ms_ticker_attach(ticker,soundread);
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ms_ticker_attach(ticker,rtprecv);
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</PRE>
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<H1>Code to unlink the filters and stop the graph sample</H1>
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<PRE>
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ms_ticker_detach(ticker,soundread);
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ms_ticker_detach(ticker,rtprecv);
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ms_filter_unlink(stream->soundread,0,stream->encoder,0);
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ms_filter_unlink(stream->encoder,0,stream->rtpsend,0);
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ms_filter_unlink(stream->rtprecv,0,stream->decoder,0);
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ms_filter_unlink(stream->decoder,0,stream->dtmfgen,0);
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ms_filter_unlink(stream->dtmfgen,0,stream->soundwrite,0);
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if (rtp_session!=NULL) rtp_session_destroy(rtp_session);
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if (rtpsend!=NULL) ms_filter_destroy(rtpsend);
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if (rtprecv!=NULL) ms_filter_destroy(rtprecv);
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if (soundread!=NULL) ms_filter_destroy(soundread);
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if (soundwrite!=NULL) ms_filter_destroy(soundwrite);
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if (encoder!=NULL) ms_filter_destroy(encoder);
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if (decoder!=NULL) ms_filter_destroy(decoder);
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if (dtmfgen!=NULL) ms_filter_destroy(dtmfgen);
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if (ticker!=NULL) ms_ticker_destroy(ticker);
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</PRE>
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*/ |