Universal Encoding Parameters for Screencams
- 7-2-2009
- Categorized in: Producing screencams
Before starting the codec-specific discussions, let’s examine the
encoding decisions that should apply to all codecs, starting with the
video side of the equation. For discussion purposes, I’ll use the
Windows Media 9 encoding controls from Sorenson Squeeze. Taking the
controls from the top, let’s start with Method, which is often
called bitrate control: Use 2-pass variable bitrate encoding, as shown
in the example, since this allows the codec to vary the bitrate
according to encoding complexity, which should improve overall quality.
However, you should use a constrained VBR technique to make sure that your viewers can reasonably stream the file; otherwise, data spikes could interrupt playback. That’s why I checked the Constrain Maximum Data Rate box about halfway down the screen. My rule of thumb is a maximum data rate of 200% of the target, though Waggoner recommended closer to 400% in his tutorial.
Figure 2. The WMV9 Encoding controls from Sorenson Squeeze.
I produce all screencams at 15 fps; anything less can appear choppy, and anything more is usually a waste since it won’t be noticed. I use a keyframe setting of between 10 and 20 seconds since more frequent keyframes can degrade quality and cause visible pulsing, or slight screen updates that occur at each keyframe. More importantly, make sure that both forced and natural keyframes are enabled so the encoder will insert keyframes at scene changes, a process that also helps to promote quality.You can see this control in Episode Pro in Figure 3.
Figure 3. Make sure to enable "Natural" key frames (or key frames at scene changes) when available.
For audio, I like mono because most screencams are recorded with a mono microphone, so encoding in stereo simply means duplicating the mono signal into both right and left channels and encoding them separately. This doubles the compression ratio necessary to achieve the target, which can degrade quality. Note that saving the file in mono doesn’t mean that your listeners will only hear the audio from one of their two speakers; instead, the player will push the same signal to both speakers in the system.
Figure 4. Use mono audio for screencams, since most microphones only record mono.
If speech is the primary content in your audio, 22 kHz should do just fine, as should a data rate of 32Kbps. When available, you should use variable bitrate encoding for your audio; otherwise, the encoder will devote the same data rate to intervals of silence as it will to speech and/or introductory music. If your audio content has significant periods of high-quality music or consistent background music, you may need to boost these parameters further, but these should do fine for most speech-dominated screencams.
Table 1 contains a summary of these parameters for easy scan-ability; now let’s move to the codec specific sections.
Table 1. Recommended generic encoding settings.
Now, let’s move to the codec-specific sections.
However, you should use a constrained VBR technique to make sure that your viewers can reasonably stream the file; otherwise, data spikes could interrupt playback. That’s why I checked the Constrain Maximum Data Rate box about halfway down the screen. My rule of thumb is a maximum data rate of 200% of the target, though Waggoner recommended closer to 400% in his tutorial.
Figure 2. The WMV9 Encoding controls from Sorenson Squeeze.
I produce all screencams at 15 fps; anything less can appear choppy, and anything more is usually a waste since it won’t be noticed. I use a keyframe setting of between 10 and 20 seconds since more frequent keyframes can degrade quality and cause visible pulsing, or slight screen updates that occur at each keyframe. More importantly, make sure that both forced and natural keyframes are enabled so the encoder will insert keyframes at scene changes, a process that also helps to promote quality.You can see this control in Episode Pro in Figure 3.
Figure 3. Make sure to enable "Natural" key frames (or key frames at scene changes) when available.
For audio, I like mono because most screencams are recorded with a mono microphone, so encoding in stereo simply means duplicating the mono signal into both right and left channels and encoding them separately. This doubles the compression ratio necessary to achieve the target, which can degrade quality. Note that saving the file in mono doesn’t mean that your listeners will only hear the audio from one of their two speakers; instead, the player will push the same signal to both speakers in the system.
Figure 4. Use mono audio for screencams, since most microphones only record mono.
If speech is the primary content in your audio, 22 kHz should do just fine, as should a data rate of 32Kbps. When available, you should use variable bitrate encoding for your audio; otherwise, the encoder will devote the same data rate to intervals of silence as it will to speech and/or introductory music. If your audio content has significant periods of high-quality music or consistent background music, you may need to boost these parameters further, but these should do fine for most speech-dominated screencams.
Table 1 contains a summary of these parameters for easy scan-ability; now let’s move to the codec specific sections.
Table 1. Recommended generic encoding settings.
Now, let’s move to the codec-specific sections.
Thankyou