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You may have half an hour of video footage from the camcorder, but you probably need to make an editorial decision and select the most interesting three minutes or so for the exported Internet video. Avidemux has a simple editing feature, based on selection points, that can help you accomplish this easily; either by cutting out selected parts that you don't want or by exporting an individual selection that you do want.

In the lower-right corner of the Avidemux interface, under the label Selection, are the letters A and B with numbers next to them. These are the video frame numbers that correspond to selection points A and B. You set the points with the Selection start button (which has an A icon button) and Selection end button (with a B icon button) in the transport controls, at lower left in the main window. You may find it helpful to use the jog wheel, which is a gray control with a small red vertical line in the middle of it, just above the Selection A and B numbers. You can use the jog wheel to skip backward and forward through the video material and find your perfect start and edit points for the shortened video. When you're working with compressed video on the input side, it's best to cut at a key frame for the start point; otherwise, the first few frames of your edited video may be missing data. (Compressed video uses key frames that contain all the data and in-between frames where data is thrown away, as a means of reducing file size.)

When you know the start point of your edit, drag the timeline slider to that point, use the double-headed arrow icons in the transport to find the nearest key frame, and click the Selection start button. Then, drag the slider to the end point, and click the Selection end button. A small square bracket appears on the timeline at each position, and the Selection numbers at lower right display the corresponding video frame numbers (see Figure 11-13). The Time box below the transport controls gives you an idea of how long your edit is in minutes and seconds, which is more user-friendly than the frame count.

Figure 11-13. The selection points set with the A and B transport buttons are shown as square brackets on the timeline.

Figure 11-13. The selection points set with the A and B transport buttons are shown as square brackets on the timeline.

Exporting a selection is the same as exporting the entire movie; click the Save button on the main tool bar, beneath the main menu bar. A file export dialog opens, in which you must specify the correct file extension for your output video file (this isn't done automatically for you). In the case of H.264 video inside an MPEG-4 container, the standard filename suffix is .mp4, although Apple's iTunes store uses the nonstandard .m4v extension for the same thing. Click the Save button, and the Encoding dialog opens, showing the statistics from the x264 conversion (see Figure 11-14). If you have a lot of video material to encode, and you're leaving the PC or laptop on overnight, you can select the "Shut down computer when finished" check box. This handy feature enables you to go out for pizza instead of ordering another delivery!

Encodrng,..

Phase:

Encoding

Video Codec:

x264

Audio Codec:

MP3

Container:

MP4

Video Size: 1MB Audio Size: OMB Total Size: 1MB

Processed Frames:

676

Total Frames:

4764

Quantiser:

27

Average Bitrate:

mkß/5

Elapsed:

00:00:39

Time Remaining:

3 minutes

Frames/sec:

17.tJ7

14%

L i Shut daw n computer ä her fini s hed Priority:

'iL:r~ E.

Figure 11-14. Encoding a video with x264 can take some time, particularly if your computer is slow. Here, my laptop is managing 17 frames per second.

When the encoding is complete, a small dialog box pops up to let you know. It's important to test the playback of your video before you upload it to the Internet: if you find mistakes after uploading, the web forms that web sites like YouTube use become tedious as you fill them in repeatedly. The GNOME interface for MPlayer (Ubuntu package gnome-mplayer) has the menu option View > Details, revealing the format and codecs of the clip you're reviewing (see Figure 11-15).

underwater.mp4 - GNOME MFlayer

File Edit View Help

BBIlT

underwater.mp4

Video Details

Video Size: Video Format: Video Codec: Video FPS: Video Bitrate:

Audio Details

Audio Codec: Audio Channels: Audio Bitrate: Audio Sample Rate:

480 x 360 AVC1 FFH264 2 5. ODO OKb/S

Figure 11-15. Check your edited video in a program like GNOME MPlayer before uploading it to the Internet, so you don't waste time later. In this example, the statistic for Video Bitrate is clearly wrong, as is the Audio Sample Rate, but the rest of the details are useful. AVC1 is another name for the MPEG-4 Part 10 or H.264 video format. The codec labeled MAD here relates to the libmad decoding library for MP3.

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