[英]Streaming video using a non-blocking FIFO in linux/bash
我正在努力實現以下目標:
由於網絡連接可能不穩定,例如WiFi路由器可能不在范圍內,因此流媒體傳輸不會干擾視頻寫入磁盤,這一點很重要。
為此,我嘗試的第一件事是:
#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 &> $netcat_log &
流式傳輸效果很好。 但是,當我關閉路由器,模擬網絡問題時,我的$ video_out被切斷了。 我認為這是由於netcat_fifo造成的背壓。
我在stackexchange上找到了一個關於非阻塞FIFO的解決方案,方法是用ftee替換tee:
現在,它可以防止$ video_out受流影響,但是流本身非常不穩定。 最好的結果是使用以下腳本:
#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 &
當我檢查mbuffer日志時,我診斷出一個FIFO在大多數時間都是空的,但峰值為99-100%。 在這些高峰期間,我的mplayer接收器端在解碼視頻時遇到很多錯誤,大約需要5秒鍾才能恢復。 在此間隔之后,mbuffer日志再次顯示一個空的FIFO。 empty-> full-> empty一直在繼續。
我有兩個問題:
我對此進行了一些嘗試,並且在我的Raspberry Pi 3上似乎可以很好地運行。它的注釋很好,因此應該很容易理解,但是您可以隨時詢問是否有任何問題。
基本上有3個線程:
主程序-它不斷從raspivid
讀取其stdin
並將其循環放入一堆緩沖區中
磁盤寫入器線程-它不斷循環瀏覽緩沖區列表,等待下一個緩沖區變滿。 當緩沖區已滿時,它將內容寫入磁盤,將緩沖區標記為已寫入,然后移至下一個緩沖區
fifo編寫器線程-它不斷循環瀏覽緩沖區列表,等待下一個緩沖區變滿。 當緩沖區已滿時,它將內容寫入fifo,刷新fifo以減少延遲,並將緩沖區標記為已寫入並移至下一個緩沖區。 錯誤將被忽略。
因此,這是代碼:
////////////////////////////////////////////////////////////////////////////////
// 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;
}
}
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