TelVue CloudCast - Manual (Page 5)

TelVue ® CloudCast TM User Manual / v. 4.1.0 / June 2014
© 2014 TelVue Corporation 16000 Horizon Way, Suite 500, Mt. Laurel, NJ 08054
CloudCast
TM is a trademark of TelVue Corporation 800-885-8886 / www.telvue.com
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Most source video these days is in the HD ratio of 16:9. If you have older SD videos in 4:3 aspect
ratio, make sure the transcoding process does not “stretch” the final video if exporting to HD
16:9. When transcoding source content that is 16:9 into 4:3 container, “pillarboxes” – black bars on
either side of the video – are typically added. When transcoding source content that is 4:3 into a 16:9
container, the content is usually “letterboxed”.
Image Scanning:
For online video, always encode with progressive scanning, not interlaced. This is the meaning of the
‘i’ or the ‘p’ in the resolution measurement (e.g., 1080p for HD video).
The difference is:
1. Interlaced: Traditional television or video display, where half the picture appears on the screen
at a time and the other half follows an instant later. This scanning method uses odd then even lines
that combine to produce an interlaced frame. The problem for VOD is that not all video players will
de-interlace the video.
2.
Progressive: The entire picture is painted at once, all line fields appear on the screen at the
same time. This scanning method uses both odd and even lines in a progressive path (one-after-
the-other) to produce a progressive frame.
Frame Rate:
Frame rate is often set by your non-linear editing based on the file format you choose. For H.264 and
MPEG-4, the default is 29.97 FPS, the NTSC standard. 30 FPS is also very commonly used in video
streamed over the Internet.
Audio File Format:
For H.264 and MPEG-4, the default and recommended audio format is AAC. it a very advanced codec
that achieves high quality with low bit rates.
Audio Sampling Rate:
For H.264 and MPEG-4, the default sampling rate is 44.1kHz. 48 kHz is the standard audio sampling
rate used by professional digital video equipment such as tape recorders, video servers, vision mixers,
etc.
Audio Channels:
While Mono offers a smaller file size, Stereo offers more optimal playback with two distinct audio
channels. If your source only has one channel of sound, there’s little reason to then transcode it to
stereo sound. But if your source was recorded with stereo sound, most people would opt to retain
those distinct audio channels and transcode with stereo sound.
Audio Bit Rate/Data Rate:
Similar to video bit rate, this corresponds to the quality of the audio. AAC (advanced audio codec) can
achieve better quality sound compared with MP3 at the same bit rate. Common bit rates:
•
SD: 32 Kbps-96 Kbps
•
HD: 128 Kbps-192 Kbps
Passes:
Some encoders allow you to perform “2-pass” encoding on VOD content. While each encoder will have
a slightly different interpretation of what this means, 2-pass encoding typically means that the
encoder will first scan the video once to determine the optimal encoding method, and then actually
perform the encoding on the second pass. This is typically paired with variable bit rate encodings, so
that the encoder has better anticipation of when it needs to increase and decrease the bit rate.
Note that 2-pass encoding will take longer than 1-pass, and may not provide a dramatic improvement
to quality.