最近在做安卓下UVC的一个案子。正好之前搞过ST方案的开机广告，这个也是我少数最后没搞成功的项目。当时也有点客观原因，当时ST要退出机顶盒市场，所以一切的支持都停了，当时啃他家播放器几十万行的代码，而且几乎没有文档，真的是非常痛苦。后面虽然功能是搞出来了，但是不稳定，持续几次后就会crash。
还记得当时最后到底层ST是用的滑动窗口缓存，双指针，一个写指针和一个读指针，当时我做了一个管道往缓存中注数据。估计还是没有完全吃透，某些细节处理有问题。正好现在又做到类似项目，所以简单总结总结相关要点。主要就是共享内存，滑动窗口，双缓冲，环形缓冲这些内容。
下面是一个简单的具有读写指针的循环缓冲区。
#include <iostream>
#include <vector>
#include <stdexcept>template<typename T>
class MediaQueue {
public:explicit MediaQueue(size_t size): buffer(size), readPtr(0), writePtr(0), count(0), maxSize(size) {}// 添加一个元素到队列中void enqueue(const T& item) {if (isFull()) {throw std::overflow_error("Queue is full");}buffer[writePtr] = item;writePtr = (writePtr + 1) % maxSize;++count;}// 从队列中读取一个元素T dequeue() {if (isEmpty()) {throw std::underflow_error("Queue is empty");}T item = buffer[readPtr];readPtr = (readPtr + 1) % maxSize;--count;return item;}// 检查队列是否为空bool isEmpty() const {return count == 0;}// 检查队列是否已满bool isFull() const {return count == maxSize;}// 获取队列中的元素数量size_t size() const {return count;}// 获取队列的最大容量size_t capacity() const {return maxSize;}private:std::vector<T> buffer;size_t readPtr;size_t writePtr;size_t count;size_t maxSize;
};
还有一种叫做乒乓buffer
就是两个buffer，一个读一个写，写完之后交换。
#include <iostream>
#include <vector>
#include <thread>
#include <mutex>
#include <condition_variable>
#include <cstring> // For memcpy
#include <chrono> // For sleepclass PingPongBuffer {
public:PingPongBuffer(size_t bufferSize): bufferSize(bufferSize), readBufferIndex(0), writeBufferIndex(1), buffers(2, std::vector<char>(bufferSize)) {}// 写入数据到当前写缓冲区void write(const char* data, size_t size) {std::unique_lock<std::mutex> lock(mutex);while (writeBufferFull) {condVar.wait(lock);}if (size > bufferSize) {throw std::overflow_error("Data size exceeds buffer capacity");}std::memcpy(buffers[writeBufferIndex].data(), data, size);writeBufferFull = true;readBufferEmpty = false;swapBuffers();condVar.notify_all();}// 从当前读缓冲区读取数据void read(char* data, size_t size) {std::unique_lock<std::mutex> lock(mutex);while (readBufferEmpty) {condVar.wait(lock);}if (size > bufferSize) {throw std::underflow_error("Data size exceeds buffer capacity");}std::memcpy(data, buffers[readBufferIndex].data(), size);readBufferEmpty = true;writeBufferFull = false;condVar.notify_all();}private:void swapBuffers() {std::swap(readBufferIndex, writeBufferIndex);}size_t bufferSize;int readBufferIndex;int writeBufferIndex;std::vector<std::vector<char>> buffers;bool readBufferEmpty = true;bool writeBufferFull = false;std::mutex mutex;std::condition_variable condVar;
};void producer(PingPongBuffer& buffer) {const char* messages[] = {"Message 1", "Message 2", "Message 3"};for (const char* message : messages) {std::this_thread::sleep_for(std::chrono::seconds(1)); // Simulate workbuffer.write(message, std::strlen(message) + 1);std::cout << "Produced: " << message << std::endl;}
}void consumer(PingPongBuffer& buffer) {char data[1024];for (int i = 0; i < 3; ++i) {buffer.read(data, 1024);std::cout << "Consumed: " << data << std::endl;}
}int main() {size_t bufferSize = 1024;PingPongBuffer buffer(bufferSize);std::thread producerThread(producer, std::ref(buffer));std::thread consumerThread(consumer, std::ref(buffer));producerThread.join();consumerThread.join();return 0;
}
空了有时间看看V4L2和ffmpeg这方面的内容再更新一下吧。。。
