24 October, 2013

Create Counting Video


On a couple of occasions, I've had the need to create a source video for video processing and testing video processing commands.  A common need is to create a counting video by generating a series of frames and stitching them together at a pre-defined frame rate.

Below is a mechanism for doing so;


$ cat createVideo 
#!/bin/bash

ws=/var/tmp/cache
rm -rf $ws
mkdir -p $ws

for i in `seq 300`; do
  N=$(printf %03d $i)
  convert -size 640x480 -background white -fill black -pointsize 120 -gravity center label:$i $ws/frame-$N.jpg
done

ffmpeg -y -r 2/1 -i $ws/frame-%03d.jpg -r 30/1 $ws/video.avi
mplayer $ws/video.avi


Cheers.

18 October, 2013

Formatting Numerics With Bash

A repeated need I've encountered is a need to format a numeric with leading zeros, similar to the common form used in C.  Typically, I take a over-complicated approach of comparing the number to >100 or >10 and pre-pending leading zeros.

After investigating alternative approaches with good 'ole Google, the better approach is shown below;


$ cat /tmp/go 
#!/bin/bash

for i in `seq 100`; do
  N=$(printf %03d $i)
  echo $N
done

Cheers.

11 October, 2013

FFMpeg Cropping Videos

Recently had a need to crop videos using FFMpeg, thought it worth sharing. Starting with the initial video:
video

$ ffmpeg -i ExSlyoVTX3I.flv -vf crop=160:120:10:10 -sameq /tmp/out.mp4

The result is a cropped video 160x120 with an offset of 10,10 from the upper left-hand corner.
video


Cheers.

05 October, 2013

Google ProtoBuff + ZeroMq -- Python

In our last post, we combined ZeroMq & Google Protobuf, a combination that enables heterogeneous distributed computing systems.  The last post integrated the two using C++, this post will focus on integrating the two using Python.  In the end, we'll have an example that can communicate with the previous C++ example seamlessly.

Below is a Makefile, used to create and clean up Google Protobuf message files.


$ cat Makefile

msgs:

 ${SH} protoc -I=. --python_out=. Messages.proto



clean:

 ${RM} Messages_pb2.py


Our sender script is below, notice the change is that of the content exchanged, specifically the serialized protobuff message.


$ cat sender
#!/usr/bin/python
import zmq;
import time;
import Messages_pb2
context = zmq.Context();
pub=context.socket(zmq.PUB);
pub.bind("tcp://127.0.0.1:8000");
for i in range(0,10):
  p=Messages_pb2.Person();
  p.id=i;
  p.name="fatslowkid";
  print "iteration",i
  pub.send(p.SerializeToString());
  time.sleep(1);

The receiver;

$ cat receiver
#!/usr/bin/python
import zmq;
import time;
import Messages_pb2
context = zmq.Context();
sub=context.socket(zmq.SUB);
sub.connect("tcp://127.0.0.1:8000");
filter=""
sub.setsockopt(zmq.SUBSCRIBE, filter);
for i in range(0,20):
  print "waiting on msg"
  M=sub.recv();
  p=Messages_pb2.Person();
  p.ParseFromString(M);
  print "received",p
  print "> " + p.name;
  print p.id;

The sender/receiver can be used together, or used with the previous C++ example.

Cheers.