What are you going to do when…
- The content you’re going to use for a show is being specially created for the gig, and the art department comes to you to ask about the media server’s specs?
- During the first day of rehearsal, the client hands you a JPEG of one of the corporate VIPs and wants to use it in the show the next day?
- You use your video camera to capture a beautiful sunset in an exotic location and you want to use it on your current fashion show? What’s the common theme in all of the above scenarios? The content will not all be correctly optimized, and it will need to be re-rendered and exported in a new format before it can be used in the media server properly. As the programmer of a media server, familiarizing yourself with the manufacturer’s specs regarding codecs and file types is an important part of your role.
Garbage In, Garbage Out
Remember this rule: If you put poorly rendered content into a server, the media server will output poor graphics. Low resolution images and movies that are formatted in the wrong file type or with the wrong codec are examples of poorly rendered content to avoid. Why? Lo-res images are difficult to scale up without getting visibly distorted and pixelated. That’s not to say that they can’t be used, but the results you will get with them will usually not be acceptable. High-resolution images are generally better off to start with as they allow more room to scale up or down from within the media server. And movies rendered at a higher resolution than required task the server’s processor more, and cause it to play back frame rates slower. Knowing and adhering to these things ahead of time means you won’t waste your time (nor the LD’s or the client’s) with content that can’t be used.
So, what do you do with that home movie of the CEO’s last office party, and what can you do in order to use it in the show? Well, depending on the condition of the content when you get it, there’s no easy answer to that question. Let’s start with the file type.
File Types
Two very common file types of movies that you will likely encounter when working with media servers are AVI and MOV. AVI files are usually preferred on PCs, while MOV files are the favorites of Macs. What’s the difference? Who wants to know? There is no “best” or rule of thumb to follow in every application. Simply put, the type of media server you will be using determines the format.
Codecs
What is a codec, you ask? (Well, maybe you didn’t!) To those of us in the lighting world, this is a new and very important term to know and embrace. It affects the playback performance of the content more than any other single attribute of content creation. Codecs (Compression-Decompression) encode a signal for transmission, storage or encryption, and decode it for viewing or editing. There are hundreds of different compression formats and new ones are created frequently due to the delicate balance between the quality of the video, the quantity of the data needed to represent it (which is known as the bit rate), the complexity of the encoding and decoding algorithms, robustness to data losses and errors, ease of editing and a number of other factors. Options are available to fit a variety of applications, so choosing the right one for your media server is imperative.
Some examples of codecs currently being used in some media servers include Cinepak, Sorenson, PhotoJPeg-Med and DV-NTSC.
Interlaced vs. Progressive Scan
The last element to cover on this topic is interlacing. This is going to boil down to the media server, once again. If the system is optimized for non-interlaced images, and you try to play an interlaced image on it, you are going to see many problems with the appearance, including tearing and horizontal scan lines in the image.
Quick! Name a common place where interlaced video is used. OK, so you knew this one already: Yes, on your very own television set. Do you know how that works? While progressive scan (de-interlaced) video means that every pixel on the screen is refreshed in order (in the case of a computer monitor) or simultaneously (in the case of film), interlaced video is refreshed to the screen twice every frame. First, every even-numbered scan line is refreshed, followed by every odd-numbered scan line (the electron gun at the back of the cathode ray tube shoots all the correct phosphors on the even-numbered rows of pixels first, and then moves to the odd-numbered rows). Since the frame rate of NTSC is 29.97 frames per second, the screen is actually being partially redrawn 59.94 times per second. So if you try to take content that is interlaced and play it back on a non-interlaced media server, you are going to be missing some bits of data in the image in between each row, and the image quality is going to be greatly affected. You probably won’t like what you see. And neither will your client.
File types, codecs and de-interlacing are three very important terms to know and understand when working with content. Your media server will appreciate and reward you for it. In upcoming columns, we’ll continue with content prep tips and hardware settings.
Vickie Claiborne is a freelance programmer and can be reached at vclaiborne@plsn.com.
