Using FFmpeg to replace video frames

Machine learning algorithms for video processing typically work on frames (images) rather than video.

In a typical use-case, FFmpeg can be used to extract images from video – in this example, a 50-frame sequence starting at 1:47:

>ffmpeg -i input.vid -vf “select=’gte(t,107)*lt(selected_n,50)'” -vsync passthrough ‘107+%06d.png’

Omit the -vf option if extracting the entire video. . . . → Read More: Using FFmpeg to replace video frames

FFmpeg lossless filtering

Preserving Data

Running a simple FFmpeg filter command:

>ffmpeg -i input.vid -filter_complex “[v:0]copy” output.vid

… one might expect the output video to be the same as the input video. Note that both input and output videos use the same container format (file name extension), and the command just uses the “copy” (do nothing) filter, . . . → Read More: FFmpeg lossless filtering

https and the browser conspiracy

While Google promotes HTTPS Everywhere, browsers have been working with a certifying authority oligopoly for many years promoting and enforcing an industry based on perception.

https: The good and the bad

The ‘s’ in https stands for ‘secure’ and indicates use of the SSL or TLS protocol. The SSL protocol serves 2 primary purposes:

Verification: . . . → Read More: https and the browser conspiracy

HTTP DDoS: “Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1)”

Our servers were attacked recently by a constant stream of HTTP POST requests. The requests were coming in from a large range of IP addresses, at a rate of about 5-10 per second, with random POST data. However, all the requests had the same UserAgent, they always accessed the non-www form of the same domain, . . . → Read More: HTTP DDoS: “Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1)”

Virtualmin + SFTP + chroot

This guide examines setting up chroot’ed SFTP-only user accounts under Virtualmin.

The Rationale:

SFTP is a secure alternative to FTP and FTPS that uses SSH. With this setup, no FTP server is needed, as the native sshd server is used instead, SSH does not require an SSL certificate (like FTPS), and is usually considered more . . . → Read More: Virtualmin + SFTP + chroot

Linux memory leak detection

Tracking down the source of a memory leak in Linux is not always straightforward…

Signs of a Memory Leak:

Typically, the first sign of a memory leak is the oom-killer. If programs start dying inexplicably, check the system log (usually /var/log/messages) for evidence of the oom-killer in action. This should be accompanied by low memory . . . → Read More: Linux memory leak detection

Compiling programs in Fedora

Say you want to install a program in Fedora…

Before Compiling:

Many programs are available easily in the Fedora repositories via yum.

If you don’t already have a graphical package management tool, then install PackageKit or yumex. If you prefer the command-line, then (as root / under sudo) use: >yum search <program> to see if . . . → Read More: Compiling programs in Fedora