在linux / bash中使用非阻塞FIFO流式传输视频

Posted 2021-04-20

我正在努力实现以下目标：

• 将我的Raspberry Pi相机中的视频写入磁盘，不受任何流式干扰
• 通过网络流式传输相同的视频优化延迟

重要的是流不会干扰正在写入磁盘的视频，因为网络连接可能不稳定，例如WiFi路由器可能超出范围等。

要做到这一点，我尝试的第一件事是：

#Receiver side
FPS="30"
netcat -l -p 5000 | mplayer -vf scale -zoom -xy 1280 -fps $FPS -cache-min 50 -cache 1024 - &

---

#RPi side
FPS="30"
mkfifo netcat_fifo
raspivid -t 0 -md 5 -fps $FPS -o - | tee --output-error=warn netcat_fifo > $video_out &
cat netcat_fifo | netcat -v 192.168.0.101 5000 &> $netcat_log &

流媒体工作得非常好。但是，当我关闭路由器，模拟网络问题时，我的$ video_out被切断了。我认为这是由于netcat_fifo的反压。

我在stackexchange找到了一个关于非阻塞FIFO的解决方案，通过用ftee替换tee：

Linux non-blocking fifo (on demand logging)

它现在阻止我的$ video_out受到流媒体的影响，但是流媒体本身非常不稳定。最好的结果是使用以下脚本：

#RPi side
FPS="30"
MULTIPIPE="ftee"
mkfifo netcat_fifo
raspivid -t 0 -md 5 -fps $FPS -o - | ./${MULTIPIPE} netcat_fifo > $video_out &
cat netcat_fifo | mbuffer --direct -t -s 2k 2> $mbuffer_log | netcat -v 192.168.0.101 5000 &> $netcat_log &

当我检查mbuffer日志时，我诊断出一个大部分时间仍为空的FIFO，但具有99-100％利用率的峰值。在这些峰值期间，我的mplayer接收方在解码视频时有很多错误，需要大约5秒才能恢复。在此间隔之后，mbuffer日志再次显示空FIFO。 empty-> full-> empty继续打开。

我有两个问题：

• 我使用正确的方法来解决我的问题吗？
• 如果是这样，我如何在保持$ video_out文件完整的同时渲染我的流媒体更强大？

答案

我有一点尝试，它似乎在我的Raspberry Pi 3上非常稳定地工作。它评论很好，所以它应该很容易理解，但你可以随时询问是否有任何问题。

基本上有3个线程：

• 主程序 - 它不断从stdin读取它的raspivid并循环地将数据放入一堆缓冲区
• 磁盘写入程序线程 - 它不断循环遍历缓冲区列表，等待下一个缓冲区变满。当缓冲区已满时，它会将内容写入磁盘，将缓冲区标记为已写入并移至下一个缓冲区
• fifo writer线程 - 它不断循环遍历缓冲区列表，等待下一个缓冲区变满。当缓冲区已满时，它会将内容写入fifo，刷新fifo以减少滞后并将缓冲区标记为已写入并移至下一个缓冲区。错误被忽略。

---

所以，这是代码：

////////////////////////////////////////////////////////////////////////////////
// main.cpp
// Mark Setchell
//
// Read video stream from "raspivid" and write (independently) to both disk file
// and stdout - for onward netcatting to another host.
//
// Compiles with:
//    g++ main.cpp -o main -lpthread
//
// Run on Raspberry Pi with:
//    raspivid -t 0 -md 5 -fps 30 -o - | ./main video.h264 | netcat -v 192.168.0.8 5000
//
// Receive on other host with:
//    netcat -l -p 5000 | mplayer -vf scale -zoom -xy 1280 -fps 30 -cache-min 50 -cache 1024 -
////////////////////////////////////////////////////////////////////////////////
#include <iostream>
#include <chrono>
#include <thread>
#include <vector>
#include <unistd.h>
#include <atomic>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>

#define BUFSZ    65536
#define NBUFS    64

class Buffer{
   public:
   int bytes=0;
   std::atomic<int> NeedsWriteToDisk{0};
   std::atomic<int> NeedsWriteToFifo{0};
   unsigned char data[BUFSZ];
};

std::vector<Buffer> buffers(NBUFS);

////////////////////////////////////////////////////////////////////////////////
// This is the DiskWriter thread.
// It loops through all the buffers waiting in turn for each one to become ready
// then writes it to disk and marks the buffer as written before moving to next
// buffer.
////////////////////////////////////////////////////////////////////////////////
void DiskWriter(char* filename){
   int bufIndex=0;

   // Open output file
   int fd=open(filename,O_CREAT|O_WRONLY|O_TRUNC,S_IRUSR|S_IWUSR|S_IRGRP|S_IWGRP);
   if(fd==-1)
   {
      std::cerr << "ERROR: Unable to open output file" << std::endl;
      exit(EXIT_FAILURE);
   }

   bool Error=false;
   while(!Error){

      // Wait for buffer to be filled by main thread
      while(buffers[bufIndex].NeedsWriteToDisk!=1){
   //      std::this_thread::sleep_for(std::chrono::milliseconds(1));
      }

      // Write to disk
      int bytesToWrite=buffers[bufIndex].bytes;
      int bytesWritten=write(fd,reinterpret_cast<unsigned char*>(&buffers[bufIndex].data),bytesToWrite);
      if(bytesWritten!=bytesToWrite){
         std::cerr << "ERROR: Unable to write to disk" << std::endl;
         exit(EXIT_FAILURE);
      }

      // Mark buffer as written
      buffers[bufIndex].NeedsWriteToDisk=0;

      // Move to next buffer
      bufIndex=(bufIndex+1)%NBUFS;
   }
}

////////////////////////////////////////////////////////////////////////////////
// This is the FifoWriter thread.
// It loops through all the buffers waiting in turn for each one to become ready
// then writes it to the Fifo, flushes it for reduced lag, and marks the buffer
// as written before moving to next one. Errors are ignored.
////////////////////////////////////////////////////////////////////////////////
void FifoWriter(){
   int bufIndex=0;

   bool Error=false;
   while(!Error){

      // Wait for buffer to be filled by main thread
      while(buffers[bufIndex].NeedsWriteToFifo!=1){
    //     std::this_thread::sleep_for(std::chrono::milliseconds(1));
      }

      // Write to fifo
      int bytesToWrite=buffers[bufIndex].bytes;
      int bytesWritten=write(STDOUT_FILENO,reinterpret_cast<unsigned char*>(&buffers[bufIndex].data),bytesToWrite);
      if(bytesWritten!=bytesToWrite){
         std::cerr << "ERROR: Unable to write to fifo" << std::endl;
      }
      // Try to reduce lag
      fflush(stdout);

      // Mark buffer as written
      buffers[bufIndex].NeedsWriteToFifo=0;

      // Move to next buffer
      bufIndex=(bufIndex+1)%NBUFS;
   }
}

int main(int argc, char *argv[])
{   
   int bufIndex=0;

   if(argc!=2){
      std::cerr << "ERROR: Usage " << argv[0] << " filename" << std::endl;
      exit(EXIT_FAILURE);
   }
   char * filename = argv[1];

   // Start disk and fifo writing threads in parallel
   std::thread tDiskWriter(DiskWriter,filename);
   std::thread tFifoWriter(FifoWriter);

   bool Error=false;
   // Continuously fill buffers from "raspivid" on stdin. Mark as full and
   // needing output to disk and fifo before moving to next buffer.
   while(!Error)
   {
      // Check disk writer is not behind before re-using buffer
      if(buffers[bufIndex].NeedsWriteToDisk==1){
         std::cerr << "ERROR: Disk writer is behind by " << NBUFS << " buffers" << std::endl;
      }

      // Check fifo writer is not behind before re-using buffer
      if(buffers[bufIndex].NeedsWriteToFifo==1){
         std::cerr << "ERROR: Fifo writer is behind by " << NBUFS << " buffers" << std::endl;
      }

      // Read from STDIN till buffer is pretty full
      int bytes;
      int totalBytes=0;
      int bytesToRead=BUFSZ;
      unsigned char* ptr=reinterpret_cast<unsigned char*>(&buffers[bufIndex].data);
      while(totalBytes<(BUFSZ*.75)){
         bytes = read(STDIN_FILENO,ptr,bytesToRead);
         if(bytes<=0){
            Error=true;
            break;
         }
         ptr+=bytes;
         totalBytes+=bytes;
         bytesToRead-=bytes;
      }

      // Signal buffer ready for writing
      buffers[bufIndex].bytes=totalBytes;
      buffers[bufIndex].NeedsWriteToDisk=1;
      buffers[bufIndex].NeedsWriteToFifo=1;

      // Move to next buffer
      bufIndex=(bufIndex+1)%NBUFS;
   }
}