文件voe_file.h的注释里这样写到
// This sub-API supports the following functionalities:
//
// - File playback.
// - File recording.
// - File conversion.
//
// Usage example, omitting error checking:
//
// using namespace webrtc;
// VoiceEngine* voe = VoiceEngine::Create();
// VoEBase* base = VoEBase::GetInterface(voe);
// VoEFile* file = VoEFile::GetInterface(voe);
// base->Init();
// int ch = base->CreateChannel();
// ...
// base->StartPlayout(ch);
// file->StartPlayingFileAsMicrophone(ch, "data_file_16kHz.pcm", true);
// ...
// file->StopPlayingFileAsMicrophone(ch);
// base->StopPlayout(ch);
// ...
// base->DeleteChannel(ch);
// base->Terminate();
// base->Release();
// file->Release();
// VoiceEngine::Delete(voe);
//
调用方法VoEFileImpl::StartPlayingFileAsMicrophone可实现混音
int VoEFileImpl::StartPlayingFileAsMicrophone(int channel,
const char fileNameUTF8[1024],
bool loop,
bool mixWithMicrophone,
FileFormats format,
float volumeScaling) {
WEBRTC_TRACE(kTraceApiCall, kTraceVoice, VoEId(_shared->instance_id(), -1),
"StartPlayingFileAsMicrophone(channel=%d, fileNameUTF8=%s, "
"loop=%d, mixWithMicrophone=%d, format=%d, "
"volumeScaling=%5.3f)",
channel, fileNameUTF8, loop, mixWithMicrophone, format,
volumeScaling);
...
voe::ChannelOwner ch = _shared->channel_manager().GetChannel(channel);
voe::Channel* channelPtr = ch.channel();
...
int res = channelPtr->StartPlayingFileAsMicrophone(
fileNameUTF8, loop, format, startPointMs, volumeScaling, stopPointMs,
NULL);
if (res) {
WEBRTC_TRACE(
kTraceError, kTraceVoice, VoEId(_shared->instance_id(), -1),
"StartPlayingFileAsMicrophone() failed to start playing file");
return -1;
} else {
channelPtr->SetMixWithMicStatus(mixWithMicrophone);
return 0;
}
}
在channel.cc中，两个实现方法如下：
int Channel::StartPlayingFileAsMicrophone(const char* fileName,
bool loop,
FileFormats format,
int startPosition,
float volumeScaling,
int stopPosition,
const CodecInst* codecInst) {
...
// Create the instance
input_file_player_ = FilePlayer::CreateFilePlayer(_inputFilePlayerId,
(const FileFormats)format);
...
if (input_file_player_->StartPlayingFile(
fileName, loop, startPosition, volumeScaling, notificationTime,
stopPosition, (const CodecInst*)codecInst) != 0) {
...
return -1;
}
input_file_player_->RegisterModuleFileCallback(this);
channel_state_.SetInputFilePlaying(true);
return 0;
}
void Channel::SetMixWithMicStatus(bool mix) {
rtc::CritScope cs(&_fileCritSect);
_mixFileWithMicrophone = mix;
}
参数_mixFileWithMicrophone的唯一作用地方说明：
int32_t Channel::MixOrReplaceAudioWithFile(AudioFrame* audio_input) {
...
if (input_file_player_->Get10msAudioFromFile(fileBuffer.get(), &fileSamples,
mixingFrequency) == -1) {
...
return -1;
}
if (fileSamples == 0) {
...
return 0;
}
}
...
if (_mixFileWithMicrophone) {
// Currently file stream is always mono.
// TODO(xians): Change the code when FilePlayer supports real stereo.
MixWithSat(audio_input->data_, audio_input->num_channels_, fileBuffer.get(),
1, fileSamples);
} else {
// Replace ACM audio with file.
// Currently file stream is always mono.
// TODO(xians): Change the code when FilePlayer supports real stereo.
audio_input->UpdateFrame(
_channelId, 0xFFFFFFFF, fileBuffer.get(), fileSamples, mixingFrequency,
AudioFrame::kNormalSpeech, AudioFrame::kVadUnknown, 1);
}
return 0;
}
其中还有一个方法这儿先标记一下：
int32_t Channel::MixAudioWithFile(AudioFrame& audioFrame, int mixingFrequency) {
...
{
...
// We should get the frequency we ask for.
if (output_file_player_->Get10msAudioFromFile(
fileBuffer.get(), &fileSamples, mixingFrequency) == -1) {
...
return -1;
}
}
if (audioFrame.samples_per_channel_ == fileSamples) {
// Currently file stream is always mono.
// TODO(xians): Change the code when FilePlayer supports real stereo.
MixWithSat(audioFrame.data_, audioFrame.num_channels_, fileBuffer.get(), 1,
fileSamples);
} else {
...
return -1;
}
return 0;
}
上面的StartPlayingFileAsMicrophone()的会调用FilePlayerImpl函数的StartPlayingFile()：
int32_t FilePlayerImpl::StartPlayingFile(const char* fileName,
bool loop,
uint32_t startPosition,
float volumeScaling,
uint32_t notification,
uint32_t stopPosition,
const CodecInst* codecInst) {
...
if (_fileModule.StartPlayingAudioFile(fileName, notification, loop,
_fileFormat, &codecInstL16,
startPosition, stopPosition) == -1) {
LOG(LS_WARNING) << "StartPlayingFile() failed to initialize "
<< "pcm file " << fileName;
return -1;
}
SetAudioScaling(volumeScaling);
...
return 0;
}
之后的流程与StartPlayingFileLocally播放本地音乐类似。
int32_t MediaFileImpl::StartPlayingAudioFile(
const char* fileName,
const uint32_t notificationTimeMs,
const bool loop,
const FileFormats format,
const CodecInst* codecInst,
const uint32_t startPointMs,
const uint32_t stopPointMs)
{
if(!ValidFileName(fileName))
{
return -1;
}
if(!ValidFileFormat(format,codecInst))
{
return -1;
}
if(!ValidFilePositions(startPointMs,stopPointMs))
{
return -1;
}
// Check that the file will play longer than notificationTimeMs ms.
if((startPointMs && stopPointMs && !loop) &&
(notificationTimeMs > (stopPointMs - startPointMs)))
{
WEBRTC_TRACE(
kTraceError,
kTraceFile,
_id,
"specified notification time is longer than amount of ms that will\
be played");
return -1;
}
FileWrapper* inputStream = FileWrapper::Create();
if(inputStream == NULL)
{
WEBRTC_TRACE(kTraceMemory, kTraceFile, _id,
"Failed to allocate input stream for file %s", fileName);
return -1;
}
if (!inputStream->OpenFile(fileName, true)) {
delete inputStream;
WEBRTC_TRACE(kTraceError, kTraceFile, _id, "Could not open input file %s",
fileName);
return -1;
}
if(StartPlayingStream(*inputStream, loop, notificationTimeMs,
format, codecInst, startPointMs, stopPointMs) == -1)
{
inputStream->CloseFile();
delete inputStream;
return -1;
}
rtc::CritScope lock(&_crit);
_openFile = true;
strncpy(_fileName, fileName, sizeof(_fileName));
_fileName[sizeof(_fileName) - 1] = '\0';
return 0;
}