Chapter 5 —
The Transcode Application

> This chapter introduces the Transcode application and gives a brief overview of the application and basic concepts. The chapter also includes information on:

> - Launching the Transcode Application
> - Converting AVI files to MPEG format
> - Transcode application options and defaults

Transcode Overview and Concepts

> > This section briefly describes the Transcode application. Topics include:

> > - What is the Transcode Application?
> > - About Transcode files

What is the Transcode Application?

> The Transcode application converts AVI format files containing either only video or both audio and video to MPEG format. Input can be uncompressed or compressed. The output can be MPEG-1 video, MPEG-1 systems (audio and video), or MPEG-2 video format. The AlphaVCR utility can be used to record AVI files for Transcode input and to play the output MPEG files.

About Transcode Files

> Input video can be in JPEG, Motion JPEG, Indeo 3.1, Indeo 3.2, uncompressed YUV 4:2:2, or YU12SEP format. The input audio may be 32, 44.1, or 48 kHz 16-bits per sample, mono, or stereo.

> The video data is decompressed if necessary and compressed to MPEG format. Keyframes (I-frames) in the output video appear every 12 frames, and subkeyframes (P-frames) appear every 3 frames. The audio data is compressed to MPEG audio format (Layer II).

> If the frame rate of the AVI file does not match one of the supported MPEG frame rates (23.976, 24.0, 25.0, 29.97, or 30 frames per second), it will be rounded to the nearest frame rate. If the input and output frame rates do not match, the audio and video in the output file will not be synchronized.

> The default output format is MPEG-1 systems. If the input file contains only video, or, if the input audio data cannot be converted to MPEG format, the default output format will be MPEG-1 video. The command line options can override defaults. MPEG-2 systems format is not currently supported.

Transcode Command Line Syntax

> > This section describes the Transcode command line syntax and its options. The Transcode Application is launched from the UNIX command line and does not have a graphical user interface.

> The syntax for Transcode is:

> > transcode -infile filename [-format type] [-outfile filename][-bitrate #]

> > [-noaudio] [-help]

> > where:

> > -infile filename

> > Contains the input AVI file name which has either audio and video, or video only. This is a required option.

> > [-format type]

> > Declares the output MPEG format. Valid values are mpeg1 for MPEG-1 format (default) or mpeg2 for MPEG-2 format.

> > [-outfile filename]

> > Contains the output file name for the output file. The default output file name is the input file name with an appended file extension of .trn. For example, if the input file is data.avi, the output file name will be data.avi.trn.

> > [-bitrate #]

> > Contains the target bit rate, in Kbits/second. The default rate is 1152 Kbits per second for video files and 1411.2 Kbits per second (same as 1X CDROM rate) for systems files.

> > [-noaudio]

> > Specifies that the output file will contain no audio (MPEG video format). If the input file contains video only, the default is MPEG video format. If the input file contains both audio and video, the default is MPEG systems format.

> > [-help]

> > Displays help information.