我正在努力实现以下目标：
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 &> $netcat_log &
流媒体效果非常好。但是，当我关闭路由器，模拟网络问题时，我的$ video_out被切断了。我认为这是由于netcat_fifo的背压。
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-＆gt; full-＆gt;空为继续。
我有两个问题：
答案 0 :(得分：1)
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，但你总是可以问是否有任何问题。
基本上有3个主题：
主程序 - 它不断从stdin读取raspivid并循环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
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;
}
}