Pushing file to web-browser while being written - php

Question

I have a backgrounded ffmpeg process which is outputting a audio file, I want to push this file to user web-browser while ffmpeg continues to write upon the file. I tried the below but this send 0 byte files.
// open the file in a binary mode
$fp = fopen($fname, 'rb');
// send the right headers
header('Content-Type: application/octet-stream');
header('Content-Disposition: attachment; filename='.basename($fname));
ob_end_clean();
fpassthru($fp);
exit;
ffmpeg cannot be launched from PHP/Python and output captured here.

Answer 1

The fpassthru function won't do the job here. In addition, there is going to be an issue of knowing when the file is complete.
File reading functions stop when the end of the file is reached. If there is a concurrent writer increasing the length of the file, then it's indeterminate how far along a reader will get before seeing EOF. In addition, there's no clear way - through the file operations - to know whether the file writer is done.
It may be feasible to attempt to read with timeouts using a loop like this (psuedo-code):
LOOP
READ bytes
IF count read == 0
THEN
SLEEP briefly
INCREMENT idle_count
ELSE
SET idle_count = 0
WRITE
END IF
UNTIL ( idle_count == 10 )
I can put that into PHP code if it helps.
Here is PHP code that does this with two files, in.dat and out.dat:
<?php
$in_fp = fopen("./in.dat", "r");
$out_fp = fopen("./out.dat", "w");
$idle_count = 0;
while ( $idle_count < 10 )
{
if ( $idle_count > 0 )
sleep(1);
$val = fread($in_fp, 4192);
if ( ! $val )
{
$idle_count++;
}
else
{
$idle_count = 0;
$rc = fwrite($out_fp, $val);
if ( $rc != strlen($val) )
die("error on writing of the output file\n");
}
}
Note the odd location of the sleep is to prevent sleeping one second after the last attempt to read.
I recommend setting the idle timeout limit higher than 10 for this purpose.