User guide

Encoder Presets
MainConcept H.264
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Wirecast User Guide | 154809
compresses the video to approximate this target. However, at different times
during your broadcast the bit rate may be higher or lower than the target rate.
9. Select an encoder profile from the Profile menu. Three profiles are provided:
Baseline, Main, and High. The Baseline profile is commonly used in mobile
applications. It is also used in other applications which operate with limited
processing power, storage capacity, and/or bandwidth. The Main profile is
appropriate for general-purpose applications of broadcast media, such as high-
bandwidth Internet broadcasting. The High profile provides the highest broadcast
quality encoding.
10. Key Frame (optionally) allows you to enter the number of frames. A movie is a
sequence of images and each image is called a frame. To compress video data,
most encoders take a frame and make it a reference (also known as a key). This
keyframe is sent as part of the broadcast, and all of the data after that keyframe is
relative to it. The benefit of this is that the compressor only needs to send what has
changed since the last keyframe. The main drawback of this is that over time it
becomes harder for the encoder to distinguish the frame-difference information,
especially if there is a lot of motion in the video. Another drawback is if your
viewer’s computer misses a keyframe, the video is distorted until the next keyframe
is sent. However, you can control how often the encoder makes a new keyframe by
setting the number of frames. The more keyframes you broadcast, the more
bandwidth required and less compression, but results in better quality video.
11. Check (optionally) the Timecode Every checkbox and enter the number of frames
between timecodes. Wirecast can generate timecodes embedded in the flash
stream. If a frames value of zero is entered, the timecode is never sent. Wirecast
sends metadata along with the frames. This data looks like an ONFi call. Various
timecodes and timestamps are also sent with the stream.
12. Check (optionally) Strict Constant Bitrate. When checked, it forces the Average bit
rate (see item 8 above) to maintain the exact bit rate entered. CBR pads the data
(when necessary) to meet exact bitrate specified. Disabling CBR can result in
slightly improved quality and decrease file size, but at the cost of greater bitrate
fluctuations which could prove troublesome for certain streaming destinations.
Selecting this option for recording is not recommended because it can result in
decreased quality and larger files, with no real benefit.
13. Check (optionally) Keyframe aligned. When checked, it facilitates adaptive bitrate
streaming by ensuring that keyframes from multiple streams are in sync, along with
the keyframes timestamp, DTS and PTS values. But this is true only if those other
streams also have the option turned on and have the same keyframe interval. To
accomplish this, Wirecast disables scene detection and manually inserts the
keyframe at the exact keyframe interval specified. Therefore, to ensure quality and
smooth switching in the player, the keyframe interval should be in the 1 to 4
second range. When Keyframe Aligned is enabled, absolute timestamp is also
enabled.
14. Check (optionally) the Audio Encoding (AAC) checkbox. When checked, the audio
for your broadcast is included. When unchecked, audio is absent. This is the
preferred method of producing video-only broadcasts because the presence of
silent audio uses bandwidth.