Today’s Agenda  Fill out student survey and turn in  Get to know you…  Syllabus – go over syllabus  Go over Week 11 reel  Break (10 minutes)  Discussion: What is compression?  Lecture: Introduction to Compressor 3.5  Practice #1 and Quiz #1  Questions, answers, jokes?

On-Line and Off-line Editing  To understand compression and the purpose, we must first understand how editors work, and the process of post- production.  One of the most common ways to edit is to use an online/offline workflow.  Online and offline editing are historically associated with videotape.

Off-Line Editing  The goal of Off-Line editing is to create a EDL (Edit Decision List) that will be used in putting together a final On-Line version.  Use of low-resolution copies of the original footage.  Once the major decisions are made offline, the EDL that is generated can be taken to colorist, visual effects, audio sweetening, and converted to the highest quality.

Online Editing  The process of rebuilding the project from the Offline Edit.  When the editor is finished with the Off-line edit, it is captured (or re-captured) at full resolution.  Because the online edit is performed at full resolution, only the material needed for the final edit is captured.

Make a Hard Copy of your EDL  Preview your footage and make a hard copy of a EDL in a video log; make columns with video title, timecode, duration (in/out), comments, reel number/tape number.  You can get an idea of the final product, the footage you plan to use, the footage that is missing, etc.

Example Compression(codec): Photo JPEG Frame Size: 320x240 Pixel Ratio:Square Quality: 35% Frame Rate(NTSC): 29.97fps Today, however, offline editing doesn’t have to mean low resolution editing.

Why Off-Line  Minimal storage requirements: About 40 minutes of footage=1GB of harddrive space  Less rendering time involved.  You can add effects in real time to low- resolution footage.  Requires organization and proper labeling of clips.

Other workflows of editors  Work in collaboration: editors, colorists, sound mixers, SFX artist, could all work together on the same edit, using the EDL.  E.G.: Avid Media Composer (64 bit), FCP iChat Theater

MPEG Streamclip  Download for free at  Go to the List Menu> Batch List>Add Files  Convert your files from higher resolution to low res.

What is Compression?  Compression is the reduction of data used in video or audio for multi-use.  Reduce the redundancy/similarities found in video data.  Bandwidth reduction: To reduce the volume of data to be transmitted and reduce the bandwidth required to be transmitted - this will allow you to change your store requirements for video, audio, images.  Distribution – various ways to distribute your media (online, DVD, stream, etc)

The Purpose of Compression  You have completed a film, and now it’s time to distribute the film to various forms of viewing.  The problem: Raw video and audio contains an immense amount of data.  The solution: use compression software to output your project into a format that will be compatible and appropriate for the form of viewing.

Overview: How does Compression Work?  Compression is similar to folding a letter before placing it in a small envelope so that it can be transported more easily and cheaply. Compressed data, like the folded letter, is not easily read and must first be decompressed, or unfolded, to restore it to its original form.

A bit of terminology…  A device (software or hardware) that compresses data is often know as an encoder or coder, whereas a device that decompresses data is known as a decoder. A device that acts as both a coder and decoder is known as a codec.  Examples of Codecs: Quicktime Compressor 3.5 MPEG Streamclip

Encoding versus Transcoding  Encoding: converting data from one form to another in order to save space. Usually not too destructive – transferring the media to a format. E.G. – From FCP > Quicktime  Transcoding: digital to digital transfer from an encoding – it is a destructive process.  E.G. -.mov > mpeg

How is compression possible?  Redundancy in digital video and audio.  Properties of human perception ( we have the ability to perceive slight differences in auditory and visual cues). Eyes are more receptive to brightness and the brain fills in the rest.  Digital audio> Series of sample values  Images> rectangular array of pixels  Video> a sequence of images played at a rate

Benefits of compressing  Interpolarity: enabling communication among different types of formats.  Flexibility to share projects in different formats- particularly important for independent filmmakers.  Reduce costs of getting your work previewed.

Two main types of compression Lossless vs. Lossy

Lossless Compression  Lossless compression, as the name implies, means that after compressing the video, and then decompressing it, you wind up with the exact same data as you put in.  Lossless has the advantage that no matter how many times you compress it, you still haven't lost any video data.  You don't save nearly as much space as you would with other lossy compression

Lossy Compression  This is the form of video compression most people are familiar with.  When you compress the video and then decompress it, you do not get back what you put it.  Famous lossy codecs include MPEG1, MPEG2, MPEG4 (AKA DivX3.11, DivX4/5, XviD, Quicktime MPEG4), DV (and its variants DVCAM, DVCPRO, DVCPRO50, Digital-S, etc), Wiindows Media Video, RealVideo, Sorenson, Indeo, and the classic Cinepak.

Two types of Compression: Lossless and Lossy Compression  Lossless: eliminate just redundant bits Modest reductions (for images, 2-3X on average) Decompression reproduces exact original dataset  Lossy: eliminate least important bits (too) Major reductions (up to 100X or more) Decompression reproduces only a similar copy

Compression Techniques  Compression techniques used for digital video can be categorized into three main groups:  General purpose compression techniques for any kind of data.  Intraframe compression techniques work on images.  Interframe compression techniques work on image sequences rather than individual images.

Software for Compression Among the various softwares for compression like iMovie, Apple Compressor, Sorenson Squeeze, Cleaner 6, QT can also be used for compression.

Examples of softwares for compression in this class Quicktime Mpeg Streamclip Apple Compressor FCP 7

Things to consider when compressing…  Type of media: are you using QT, MPEG1…?  Frames per second: 24, 25, vs  Audio quality: Noise reduction  De-interlacing: you need to do this otherwise you video will have artifacts (unclear outlines)  Audio and video data rates: this will determine the file size and your format for distribution  Frame size/resolution: pay attention to the size because the smaller the size, the smaller the file.  Color fidelity: the accuracy of the colors in the picture which depends on bit depth.

Terminology  Codec: Compressor/DECompressor  MPEG: Motion Picture Experts Group  Encoder, decoder, codec, transcoding