Live555源代码解读（4）下
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static ServerMediaSession* createNewSMS(UsageEnvironment& env,char const* fileName, FILE* /*fid*/)
{
// Use the file name extension to determine the type of "ServerMediaSession":
char const* extension = strrchr(fileName, '.');
if (extension == NULL)
return NULL;
ServerMediaSession* sms = NULL;
Boolean const reuseSource = False;
if (strcmp(extension, ".aac") == 0) {
// Assumed to be an AAC Audio (ADTS format) file:
NEW_SMS("AAC Audio");
sms->addSubsession(
ADTSAudioFileServerMediaSubsession::createNew(env, fileName,
reuseSource));
} else if (strcmp(extension, ".amr") == 0) {
// Assumed to be an AMR Audio file:
NEW_SMS("AMR Audio");
sms->addSubsession(
AMRAudioFileServerMediaSubsession::createNew(env, fileName,
reuseSource));
} else if (strcmp(extension, ".ac3") == 0) {
// Assumed to be an AC-3 Audio file:
NEW_SMS("AC-3 Audio");
sms->addSubsession(
AC3AudioFileServerMediaSubsession::createNew(env, fileName,
reuseSource));
} else if (strcmp(extension, ".m4e") == 0) {
// Assumed to be a MPEG-4 Video Elementary Stream file:
NEW_SMS("MPEG-4 Video");
sms->addSubsession(
MPEG4VideoFileServerMediaSubsession::createNew(env, fileName,
reuseSource));
} else if (strcmp(extension, ".264") == 0) {
// Assumed to be a H.264 Video Elementary Stream file:
NEW_SMS("H.264 Video");
OutPacketBuffer::maxSize = 100000; // allow for some possibly large H.264 frames
sms->addSubsession(
H264VideoFileServerMediaSubsession::createNew(env, fileName,
reuseSource));
} else if (strcmp(extension, ".mp3") == 0) {
// Assumed to be a MPEG-1 or 2 Audio file:
NEW_SMS("MPEG-1 or 2 Audio");
// To stream using 'ADUs' rather than raw MP3 frames, uncomment the following:
//#define STREAM_USING_ADUS 1
// To also reorder ADUs before streaming, uncomment the following:
//#define INTERLEAVE_ADUS 1
// (For more information about ADUs and interleaving,
// see <http://www.live555.com/rtp-mp3/>)
Boolean useADUs = False;
Interleaving* interleaving = NULL;
#ifdef STREAM_USING_ADUS
useADUs = True;
#ifdef INTERLEAVE_ADUS
unsigned char interleaveCycle[] = {0,2,1,3}; // or choose your own...
unsigned const interleaveCycleSize
= (sizeof interleaveCycle)/(sizeof (unsigned char));
interleaving = new Interleaving(interleaveCycleSize, interleaveCycle);
#endif
#endif
sms->addSubsession(
MP3AudioFileServerMediaSubsession::createNew(env, fileName,
reuseSource, useADUs, interleaving));
} else if (strcmp(extension, ".mpg") == 0) {
// Assumed to be a MPEG-1 or 2 Program Stream (audio+video) file:
NEW_SMS("MPEG-1 or 2 Program Stream");
MPEG1or2FileServerDemux* demux = MPEG1or2FileServerDemux::createNew(env,
fileName, reuseSource);
sms->addSubsession(demux->newVideoServerMediaSubsession());
sms->addSubsession(demux->newAudioServerMediaSubsession());
} else if (strcmp(extension, ".ts") == 0) {
// Assumed to be a MPEG Transport Stream file:
// Use an index file name that's the same as the TS file name, except with ".tsx":
unsigned indexFileNameLen = strlen(fileName) + 2; // allow for trailing "x\0"
char* indexFileName = new char[indexFileNameLen];
sprintf(indexFileName, "%sx", fileName);
NEW_SMS("MPEG Transport Stream");
sms->addSubsession(
MPEG2TransportFileServerMediaSubsession::createNew(env,
fileName, indexFileName, reuseSource));
delete[] indexFileName;
} else if (strcmp(extension, ".wav") == 0) {
// Assumed to be a WAV Audio file:
NEW_SMS("WAV Audio Stream");
// To convert 16-bit PCM data to 8-bit u-law, prior to streaming,
// change the following to True:
Boolean convertToULaw = False;
sms->addSubsession(
WAVAudioFileServerMediaSubsession::createNew(env, fileName,
reuseSource, convertToULaw));
} else if (strcmp(extension, ".dv") == 0) {
// Assumed to be a DV Video file
// First, make sure that the RTPSinks' buffers will be large enough to handle the huge size of DV frames (as big as 288000).
OutPacketBuffer::maxSize = 300000;
NEW_SMS("DV Video");
sms->addSubsession(
DVVideoFileServerMediaSubsession::createNew(env, fileName,
reuseSource));
} else if (strcmp(extension, ".mkv") == 0) {
// Assumed to be a Matroska file
NEW_SMS("Matroska video+audio+(optional)subtitles");
// Create a Matroska file server demultiplexor for the specified file. (We enter the event loop to wait for this to complete.)
newMatroskaDemuxWatchVariable = 0;
MatroskaFileServerDemux::createNew(env, fileName,
onMatroskaDemuxCreation, NULL);
env.taskScheduler().doEventLoop(&newMatroskaDemuxWatchVariable);
ServerMediaSubsession* smss;
while ((smss = demux->newServerMediaSubsession()) != NULL) {
sms->addSubsession(smss);
}
}
return sms;
}
可以看到NEW_SMS("AMR Audio")会创建新的ServerMediaSession，之后马上调用sms->addSubsession（）为这个ServerMediaSession添加一个 ServerMediaSubSession 。看起来ServerMediaSession应该可以添加多个ServerMediaSubSession，但这里并没有这样做。如果可以添加多个 ServerMediaSubsession 那么ServerMediaSession与流名字所指定与文件是没有关系的，也就是说它不会操作文件，而文件的操作是放在 ServerMediaSubsession中的。具体应改是在ServerMediaSubsession的sdpLines()函数中打开。