这一节开始我们将重新回到 MediaCodec 这一层来学习 buffer 的流转

status_t MediaCodec::dequeueOutputBuffer(size_t *index,size_t *offset,size_t *size,int64_t *presentationTimeUs,uint32_t *flags,int64_t timeoutUs) {sp<AMessage> msg = new AMessage(kWhatDequeueOutputBuffer, this);msg->setInt64("timeoutUs", timeoutUs);sp<AMessage> response;status_t err;if ((err = PostAndAwaitResponse(msg, &response)) != OK) {return err;}CHECK(response->findSize("index", index));CHECK(response->findSize("offset", offset));CHECK(response->findSize("size", size));CHECK(response->findInt64("timeUs", presentationTimeUs));CHECK(response->findInt32("flags", (int32_t *)flags));return OK;
}status_t MediaCodec::renderOutputBufferAndRelease(size_t index) {sp<AMessage> msg = new AMessage(kWhatReleaseOutputBuffer, this);msg->setSize("index", index);msg->setInt32("render", true);sp<AMessage> response;return PostAndAwaitResponse(msg, &response);
}status_t MediaCodec::renderOutputBufferAndRelease(size_t index, int64_t timestampNs) {sp<AMessage> msg = new AMessage(kWhatReleaseOutputBuffer, this);msg->setSize("index", index);msg->setInt32("render", true);msg->setInt64("timestampNs", timestampNs);sp<AMessage> response;return PostAndAwaitResponse(msg, &response);
}status_t MediaCodec::releaseOutputBuffer(size_t index) {sp<AMessage> msg = new AMessage(kWhatReleaseOutputBuffer, this);msg->setSize("index", index);sp<AMessage> response;return PostAndAwaitResponse(msg, &response);
}status_t MediaCodec::signalEndOfInputStream() {sp<AMessage> msg = new AMessage(kWhatSignalEndOfInputStream, this);sp<AMessage> response;return PostAndAwaitResponse(msg, &response);
}status_t MediaCodec::getOutputFormat(sp<AMessage> *format) const {sp<AMessage> msg = new AMessage(kWhatGetOutputFormat, this);sp<AMessage> response;status_t err;if ((err = PostAndAwaitResponse(msg, &response)) != OK) {return err;}CHECK(response->findMessage("format", format));return OK;
}