Introduction to the Basic Encoder
Reference Guide: EN8000 MPEG-4 Part 10 (H.264/AVC) Encoders
Page 1-11
ST.RE.E10233.1
Dolby Digital
If licensed, the Encoder can encode incoming audio at a sampling rate of 48 kHz to a Dolby
Digital compliant bitstream for the TS output only. Dolby Digital audio encoding incorporates
digital normalization, pre-processing (filtering), dynamic range compression and the addition of
bit-stream information. Dolby Pro Logic audio can be carried as stereo audio through the
Encoder as long as a suitably high bitrate is selected (see Annex B, Technical Specification).
The available coding modes are:
•
1/0: centre
•
2/0: left and right
Pass-thru
This is where an audio stream has already been encoded externally, prior to entering the
Encoder. Currently the Encoder is certified to handle Dolby Digital and Dolby E pre-encoded
streams for TS output only.
NOTES…
1. See
Annex F, Audio Modes for details of setting up the audio.
2.
The sampling rate for all audio encoders is fixed at 48 kHz.
1.5
VBI Line Processing Modes
With analogue video, ancillary information associated with the video image is encoded within
the vertical blanking interval (VBI) of the video image. However the VBI is not encoded as part
of the active image by the video encoding module for efficiency reasons because the VBI is
not visible to the viewer. So, this information, termed VBI data, must be carried separately in
some other form within the bitstream.
Transport of VBI Data
There are two methods to achieve this:
•
Embedding the VBI data within the video elementary stream: all video coding technologies
allow the carriage of user data associated with a video frame with the video frame
bitstream. The following data formats are handled with this method:
Closed Captions and V-chip information stored on Line 21 on top and bottom field of
each frame according to EIA-608 and EIA-708B specifications.
Wide Screen Signalling (WSS) stored on Line 23 according to ETS 300 294 and
signals the aspect ratio of the video image. For H.264/AVC bitstream, the aspect
ratio is contained within the GOP header sequence. Frame accurate switching is
enabled because a GOP header with an accompanying I frame is inserted whenever
this value changes.
•
Encapsulating the VBI data within its own elementary stream: the VBI data is contained
separately from any of the other stream. The following data formats are handled with this
method:
Neilson AMOL I and II.
18 lines of Teletext from each field of the video frame can be extracted and
packetised according to DVB specification EN 300 472.
This information is summarized in Table 1.4.
