這篇文章將介紹Stagefright中是如何和OMX video decoder傳遞buffer。
(1) OMXCodec會在一開始的時候透過read函式來傳送未解碼的data給decoder,並且要求decoder將解碼後的data傳回來
status_t OMXCodec::read(...) { if (mInitialBufferSubmit) {
mInitialBufferSubmit =
false;
drainInputBuffers();
<----- OMX_EmptyThisBuffer
fillOutputBuffers();
<----- OMX_FillThisBuffer }
... }
void OMXCodec::drainInputBuffers() { Vector<BufferInfo>
*buffers
= &mPortBuffers[kPortIndexInput];
for (i
= 0; i
< buffers->size();
++i) {
drainInputBuffer(&buffers->editItemAt(i)); } }
void OMXCodec::drainInputBuffer(BufferInfo
*info) {
mOMX->emptyBuffer(...); }
void OMXCodec::fillOutputBuffers() { Vector<BufferInfo>
*buffers
= &mPortBuffers[kPortIndexOutput];
for (i
= 0; i
< buffers->size();
++i) {
fillOutputBuffer(&buffers->editItemAt(i)); } }
void OMXCodec::fillOutputBuffer(BufferInfo
*info) {
mOMX->fillBuffer(...); }
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(2) Decoder從input port讀取資料後,開始進行解碼,並且回傳EmptyBufferDone通知OMXCodec
void OMXCodec::on_message(const
omx_message &msg) { switch (msg.type) { case omx_message::EMPTY_BUFFER_DONE: {
IOMX::buffer_id buffer
= msg.u.extended_buffer_data.buffer;
drainInputBuffer(&buffers->editItemAt(i)); } } }
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OMXCodec收到EMPTY_BUFFER_DONE之後,繼續傳送下一個未解碼的資料給decoder。
(3) Decoder將解碼完的資料送到output port,並回傳FillBufferDone通知OMXCodec
void OMXCodec::on_message(const
omx_message &msg) { switch (msg.type) { case omx_message::FILL_BUFFER_DONE: {
IOMX::buffer_id buffer
= msg.u.extended_buffer_data.buffer;
fillOutputBuffer(info);
mFilledBuffers.push_back(i);
mBufferFilled.signal(); } } }
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OMXCodec收到FILL_BUFFER_DONE之後,將解碼後的資料放入mFilledBuffers,發出mBufferFilled信號,並且要求decoder繼續送出資料。
(4) read函式在後段等待mBufferFilled信號。當mFilledBuffers被填入資料後,read函式將其指定給buffer指標,並回傳給AwesomePlayer
status_t OMXCodec::read(MediaBuffer
**buffer,
...) { ...
while (mFilledBuffers.empty()) {
mBufferFilled.wait(mLock); }
BufferInfo *info
= &mPortBuffers[kPortIndexOutput].editItemAt(index);
info->mMediaBuffer->add_ref(); *buffer
= info->mMediaBuffer; }
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