Where is the bottleneck in mjpeg broadcasting? - php

Question

I'm streaming mjpeg with PHP just like this
<?php
//example /cli/watch.php?i=0&j=200
function get_one_jpeg($i) {
$path = "img";
//$f = fopen("$path/$i.jpg", "rb");
return file_get_contents("$path/$i.jpg");
}
ini_set('display_errors', 1);
# Used to separate multipart
$boundary = "my_mjpeg";
# We start with the standard headers. PHP allows us this much
//header("Connection: close");
header("Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0");
header("Cache-Control: private");
header("Pragma: no-cache");
header("Expires: -1");
header("Content-type: multipart/x-mixed-replace; boundary=$boundary");
# From here out, we no longer expect to be able to use the header() function
print "--$boundary\n";
# Set this so PHP doesn't timeout during a long stream
set_time_limit(0);
# Disable Apache and PHP's compression of output to the client
#apache_setenv('no-gzip', 1);
#ini_set('zlib.output_compression', 0);
# Set implicit flush, and flush all current buffers
#ini_set('implicit_flush', 1);
for ($i = 0; $i < ob_get_level(); $i++)
ob_end_flush();
ob_implicit_flush(1);
# The loop, producing one jpeg frame per iteration
$i = $_GET['i'];
$j = $_GET['j'];
while ($i <= $j) {
# Per-image header, note the two new-lines
print "Content-type: image/jpeg\n\n";
# Your function to get one jpeg image
print get_one_jpeg($i);
# The separator
print "--$boundary\n";
# Sleeping for 0.1 seconds for 10 frames in second
usleep(100000);
$i++;
}
?>
But if I set a big range of images, for example, from 0 to 300, in indefinite time browser just stop showing.
It's not a specific frame or moment of time, and shows in different browsers, so I think that the causer of it is Apache.
I tried it under Apache 2.2.9 and 2.2.21 and get the same result. Under IIS Express it works even worse.
What problem it can be?

Answer 1

Based only on the info given:
10 frames per second can be a little aggresive for mjpeg if the frame size/resolution is larger. Remember, this is not mpeg where parts of the frame that are static don't get sent. Here the entire frame/image is sent every time. I would first try lowering the frame rate to around 5. If the problem improves then you know the issue is data rate, somewhere/somehow. You might be able to improve your problem at 10 fps if your code buffered some frames first then read from the buffer. That way if a frame is slow to show up your code or browser don't choke. I think you also need to limit the time your code will wait for an image to show up before giving up and continuing with the next image. Hope this helps.

Answer 2

I'm not sure if this question is still valid, but even if it's not, there is no direct answer.
I assume you are getting "image corrupt or truncated" error. My code is almost identical and I faced the same issue when using usleep(..).
The root cause is the usleep(..) placement - it should be called before print($boundary), not after. When you place it after print, browser will thing that something is wrong since it expect image directly after boundary section. IN this code immediately after boundary is usleep(..) which hold the stream for 100ms and because of that browser think that something is wrong.
Change this code:
print "--$boundary\n";
usleep(100000);
To this one:
usleep(100000);
print "--$boundary\n";
And everything will be working fine.