Thanks to its active community and incremental improvements, the Raspberry Pi has long since surpassed the point of purely experimental applications. In the meantime, the miniature PC has made itself useful in the commercial environment, for example as a controller for industrial machines.

For this article, the Raspberry Pi comes into play where previously expensive TV sets with VCRs or, in recent times, individual computers with displays have been used for advertising purposes. With Raspberry Slideshow [1] and the tiny computer, you can bring multimedia content to the screen professionally and at a very low price.

Thanks to intelligent software, the Rasp Pi can easily supplement advertising columns and billboards. You can use the Raspbian-derivative Raspberry Slideshow to play a digital photo album or fade in video sequences, which can be mixed if necessary.

The operating system is available in two functionally different versions: In contrast to the Donors' Build, the free version does not include an option for customizing the configuration over SSH. In the free version, then, certain manual modifications to configuration files can only be carried out with the help of a Linux PC, from which you can edit the corresponding files directly on the SD card.

Additionally, the freely available version only lets you play back multimedia content stored on a USB memory stick or on the Internet. Different server lists and automatic rotation of the images on the basis of existing Exif data in presentations can only be handled by the Donors' Build [2], which is available for EUR16.90.

Getting Started

Raspberry Slideshow is available as a 580MB ZIP archive on the SourceForge site. After unpacking the archive, transfer the extracted image to an SD card at least 4GB in size, although a higher capacity memory card is recommended with an expanded system partition (Figure 1).

Figure 1: With GParted, you can increase the storage capacity for the Raspberry Slideshow system.

The software copies the contents from a USB stick to the card so that files can be played back automatically, even without an external memory device. If space runs out when copying content to the SD card, the software cancels the process without an error message. As a result, the system will then only display the data in the slide show that has actually made it onto the card.

After installing the image on the SD card, start your Rasp Pi with the Slideshow system. The integration of external data sources into the network requires wired LAN access if an Raspberry Pi 2 (RPi2) is used, because the system does not detect external wireless dongles in the standard version. Even the adapters directly supported by Raspbian are not integrated during startup.

The operating system plays a video show for demonstration purposes: the northern Italian city of Verona at night. The calculator displays the show in full-screen mode and does not allow you to control it with the keyboard or mouse.

Content

To view content in the appropriate order, add an ext4 or (V)FAT filesystem to a USB stick. Create a single partition only, and then place the desired videos or pictures directly in the main directory. Raspberry Slideshow is not able to read content from a directory hierarchy.

Connect the prepared data carrier to the Rasp Pi and reboot. After powering up, the content automatically appears on the screen, with the Rasp Pi's HDMI port also transmitting audio signals. The restriction on sources in the freely available version of Raspberry Slideshow reduces the benefit somewhat: You are allowed to play a maximum of three files of mixed content with the standard version. This restriction is removed only in the commercial version.

Raspberry Slideshow uses the command-line program Fbi to display a photo slide show (JPG, PNG, BMP, and GIF) and OMXPlayer to play videos (MP4 and AVI).

If the system temporarily or continuously displays a yellow flash symbol at the top right of the screen after power-up, the power supply is not performing well enough, which could cause slide shows to stop prematurely or the system to transfer video files incompletely to the SD card, resulting in a black screen.

Make sure that the power supply of the RPi2 outputs at least 1,200mA, and for the Raspberry Pi 3 (RPi3) at least 2,500mA. Problems often arise when buying cheap power supplies from the Far East that come directly from the manufacturer: Often they do not comply with current EU standards and fail to deliver the promised performance.

Configuration

Different form factors between photos and screens often result in black edges on the sides and occasionally on the upper and lower edges. A similar phenomenon often occurs when playing back videos that were produced with a 4:3 aspect ratio.

To eliminate such unsightly edges as much as possible, expand the display area by mounting the SD memory card with the boot partition on a Linux PC and editing the /boot/config.txt file. You need to enable the disable overscan=1 line, which is commented out, simply by removing the preceding hashtag (Figure 2). After a reboot, the system displays the videos and images in full-screen mode, eliminating the annoying black borders when the image conforms to the monitor.

Figure 2: Modifying the /boot/config.txt file gives you superior image reproduction.

Another problem arises when playing back large image collections: The Fbi player uses only a relatively small buffer, causing jerky transitions when changing images. To prevent this, edit the /etc/rs.conf file located in the root partition of the SD card.

This file controls the parameters for starting the two playback programs. For Fbi, the command sequences contain the cachemem parameter, which specifies the maximum size of the buffer used. Here, you need to increase the specified value to avoid jerky transitions.

In this file, you can also modify the parameters for cross-fade effects and display time. You can also rotate images or play them in a random order (Figure 3). Detailed instructions can be found in the software's documentation [3].

Figure 3: The /etc/rs.conf file manages the player configuration.