Archive for June, 2024

Console Video edit Rotate, Merge, Scale, Trim add background music to Video files on Linux and UNIX with ffmpeg

Tuesday, June 18th, 2024

GNU / Linux and other Free as in Beer OS-es such FreeBSD and OpenBSD as well as other UNIX variants are definitely not the best platform to do Video edit, as the best one is obviosuly MAC OS-es for being a veteran in the field of graphic edit for a long time but over the time its capabilities are slowly but surely evolving. 
However Linux users can also do the basic video edit stuff quite easily with ffmpeg and few other tools.
 The general things one faces when snapshotting videos is the video might be turned around or in the wrong angle and you want it to rorate, or you have two three or more video files and you would like to merge the ones in one or you would like to Trim a period in the beginning of a Video or Trim some time you don't need out of the video at the end end, merge multiple MP3 files into single recording or including a background music to a video.

Doing such a things has a lot of possibilities with tools such as ffmpeg, imagemagick and mencoder and it is mostly useful if you're a console guy or you need to write a program that does video rorate or video merge in PHP / Perl / Python etc.

1. Rotating Videos in Linux

Rotate a Video in 90 degrees

Rotating a video assuming that you have the ffmpeg tool installed is as easy as:

# ffmpeg -i -vf "transpose=1"

Supported value arguments for ffmpeg ranspose option
0 = 90CounterCLockwise and Vertical Flip (default)
1 = 90Clockwise
2 = 90CounterClockwise
3 = 90Clockwise and Vertical Flip

2. Flip the video clip Vertically

# ffmpeg -i -vf "vflip" out2.avi

If you don't have ffmpeg, just install it with apt or yum:

On Debian 

# apt install –yes fmpeg

On Redhat based distros

# yum install -y ffmpeg

ffmpeg is easily installed by bsd ports with the package manager for example on FreeBSD it is up to :

# pkg install ffmpeg

3. Merge (Concatenating) Videos with ffmpeg / mencoder / avimerge on Linux

Go to the directory containing all the videos you would like to merge and merge them with belowsimple one liner:

# ffmpeg -f concat -i \
<(for f in $PWD/*.avi;do echo "file '$f'";done) \
-c copy output.avi

To merge multiple set of lets say ( sequential ) Video files on Linux with mencoder and produce a single video file:

# mencoder -oac copy -ovc copy 1.AVI 2.AVI 3.AVI 4.AVI -o Single-common-out-video.avi

mencoder is available also by default on most distros if not install it with:

On Deb based Linuz:

# apt install mencoder –yes

On Fedora / CentOS … rpm based:

# yum install -y mencoder

The old and now obsolete transcode audio / video converter could also be used:

 # avimerge -i file-input1.avi file-input2.avi -o output-file.avi

4. Scaling a video to a concrete resolution

It might happen to you that some video files could not be concatenated with other video file because its resolution is smaller (or different) than the recorded material,
to come around this you need to scale it.

# Scale video resolution to 1920×1080 pixels

# ffmpeg -i input-video.mp4 -vf scale=1920:1080 output-video.mp4

5. Trimming the beginning of a Video with ffmpeg

A recording will often contain parts in the beginning that you don't need and have to beto be removed from the video stream:

# Remove the first three seconds (Common scenario)

# ffmpeg -i input.mp4 -ss 3 -c copy output.mp4

6. Trimming the end of MP4 video with ffmpeg

The same is true for the end of a video materials often:

# Remove everything after 5 minutes and 32 seconds

#ffmpeg -i input.mp4 -t 00:05:32 -c copy output.mp4

Both, -ss and -t, can also be combined into one command.

7. Adding Background Music to a Video with ffmpeg

To add a concrete background music to a video stream, track the volume had to be lowered first:

7.1 Reduce the volume MP3 music file by 50% with ffmpeg

# ffmpeg -i input.mp3 -filter:a "volume=0.5" output.mp3

7.2 Combine multiple audio tracks into one single recording stream

# Concatenate multiple mp3 voice files into one
# ffmpeg -i "concat:input-song1.mp3|input-song2.mp3|input-song3.mp3" -c copy output-concatenated-single-song.mp3

One thing to consider is that once you want to add a background music stream to a video stream, both the video and the song has to be of the same length, otherwise attempts to merge the background audio track with fail
 due to the length of the audio track not matching the length of the video.
This can be resolved by generating a silent audio track and concatenating it to the end of the audio track to make the video and music match:

# Generate 33 seconds of silence
# ffmpeg -f lavfi -i anullsrc=channel_layout=5.1:sample_rate=48000 -t 33 output.mp3

Finally, to merge the audio track into the video track:

# Merge video with existing audio track and another audio track

# ffmpeg -i input.mp4 -i input.mp3 -filter_complex "[0:a][1:a]amerge=inputs=2[a]" -map 0:v

Sum it up what learned

In this article was shown how to convert multiple Videos into a single one, scaling a video to a graphics resolution, trip a video at the beginning and at the end, add background movie tracks as a sound on Linux.
As you can imagine this stuff is quite useful and used by many, many websites online to do a different Video and sound editing included in a millions of Frontend / Backend webscritt Scripts around silently doing its stuff.
There is much more to be done with this tools, but for a starter of a video edit newbies it should on Linux and enthusiasts to manage own managed small private clouds, hope this stuff will be useful for a introductionary.

Cheers ! 🙂 

How to filter an IP, and IP range or domain to access to access service with /etc/hosts.allow /etc/hosts.deny , filtering Network range to sshd tcp port 22 through sshd service

Tuesday, June 4th, 2024


If you want to filter a range of IPs to be able to or unable to access a TCP port service because someone is trying to brute force you from the network or just because you don't want a connected LAN IPs to have access to your server for whatever security reasons. The simplest way you can do IP and IP range restrictions to allow or disable access towards a Linux server via defining allow or prohibition rules in  /etc/hosts.allow and /etc/hosts.deny.

This files are there and useful since the beginning of UNIX OS-es and has been widely used on Linux in the past and rarely known by people nowadays.


The hosts.allow and hosts.deny files could be used on a Linux system to deny connection attempts from one or more IP addresses, hostnames, or domains. 
/etc/hosts.allow and /etc/hosts.deny are just a plain text configuration file with a rather simple syntax, that can be used for decades to allow or filter IPs without applying a special firewall rules like iptables locally.
It can work with any TCP wrapped service on your system. The hosts.deny file is used in conjunction with hosts.allow to determine whether a connection attempt gets accepted or denied.

In this small tutorial, you will see an example of the hosts.allow file and how to use it to allow or deny connections to IPs or networks, as well as how a simple prohibition to access SSH service only via specific IP network can be done.

For full understanding of hosts.allow / hosts.deny file, check the manuals man hosts.allow , man hosts.deny, man hosts_options, man hosts_options.

root@pcfreak:~# apropos hosts|grep -iE '^hosts.*'
hosts.equiv (5)      – list of hosts and users that are granted "trusted" r command access to your system
hosts (5)            – static table lookup for hostnames
hosts.allow (5)      – format of host access control files
hosts.deny (5)       – format of host access control files
hosts_access (5)     – format of host access control files
hosts_options (5)    – host access control language extensions

General hosts.allow / hosts.deny syntax

The /etc/hosts.allow and /etc/hosts.deny understood syntax form is: 

service : host/network

Each value is separated by a colon :

You can also supply an option, but this is not as common. We will cover some other niche choices below. More options can be added if necessary, with each one separated by another colon.

service : host/network [:

The following line would allow all traffic to the sshd service. ALL is used as a wildcard.

sshd : ALL

Few examples to allow access to SSH Daemon from IPv4 and IPv6
This line would allow connections from all hosts on the 10.11 network. Connections from all other hosts can then be denied by the hosts.deny file. This type of configuration would work as intended since the allow line precedes our corresponding deny line in the other file, thus will be triggered first.

sshd : 10.11

Accept connections from a particular IPv4 and IPv6 address

sshd :
sshd : [2a02:2143:88f1:5c00:9991:9daa:b580:aee2]


Rather than using IPs, you can also specify hostnames to accept or deny connections from.

sshd :


Accept connections from all hosts using the main domain domain name.

sshd :

You can also use a wildcard for both the service and the host/network field. This will accept all connections to any service. This would make all other rules (including those in hosts.deny) irrelevant, as all connections will be accepted by this rule before they have a chance to be denied.


The EXCEPT operator can be used to create an exception in an otherwise all allowing rule. 
For example, this rule would allow all connections from the domain name, except for one sub-domain

sshd : EXCEPT

Allow connectivity towards SSH TCP port 22 for all IP / hosts except for certain IPs and domains

To control connectivity towards sshd service via allow hosts  /etc/hosts.allow for all except a and a certain IP range:


sshd : ALL : allow
sshd : : deny
sshd : 85.5.1. : deny (1)


Disable access to all remote services to the network

Lets say if you're running the Linux as  desktop station and you want to disable access to any local services running on TCP ports

If you want to be paranoid and disable all remote access to server to any IP network, you can do it with:

# echo "ALL: ALL" >/etc/hosts.deny

Completely allow access to a certain running TCP port service on server

To allow completely access to a service

service_name : ALL : allow

Allow access for a a range of IPs subnet

You can also specifcy the IP netmask range to allow, like this:



Allow access to all server network services for a domain except for a certain domain

Enable access to ALL running server services listening on TCP port except for domain


Allow access to al services except to a service for a local port range via hosts.allow

Here is example onw how to use hosts.allow file to allow connections all running server services except access to VSFTP, coming from Local LAN IPs with netmask /24 (e.g. from the 192.168.0.x.):

ALL EXCEPT vsftpd : 192.168.0


Filtering IPs and IP Ranges from within /usr/sbin/sshd openssh service via /etc/ssh/sshd_config (allow and disable access to concrete IPs trying to brute force you)

Lets say however, you don't want to do the filtering of openssh connections via hosts.allow / hosts.deny but rather on a SSH Service level, this can be done with the following /etc/ssh/sshd_config configuration.

# vim /etc/ssh/sshd_config

Match Address *,!
    ForceCommand /bin/false

For more on the use of Match Address check documentation with man 5 sshd_config

To re-load the opensshd config

# systemctl restart sshd


Of course manually filtering villains is a tedious task and ultimately to save yourself time and inconvenience to regullary look up within /var/log/security or /var/log/messages (depending on the Linux distribution) and the configuration for SSHD to login imposters you would prefer to use fail2ban (if you're not familiar with fail2ban check out my previous article on how to easily Stop ssh bruteforce authentication attempt Attacks with fail2ban or if you want to use the Linux native way check out the article how to prevent SSH and FTP bruteforce attacks with IPtables.