Image Processing Reference
In-Depth Information
16.5.3
Track Organization
The different kinds of tracks in the file-based container might include any combination of
the different kinds of data. We'll look at those data types in this section.
16.5.3.1 Video
Coded video is stored as a sequence of frames. This “video” category
might also include groups of pictures chunked together and compressed or perhaps sin-
gle frames stored uncompressed. This is the container for the video that is processed by
the codec.
16.5.3.2 Left Eye/Right Eye Video
IMAX and other cinema formats support a
variety of interleaving schemes for mixing stereoscopic picture sequences and alternating
the delivery so that each eye sees a subtly different image that simulates the camera as a
virtual-eyeball point of view. The video might be stored as two independent streams or as
an interleaved sequence of frames with left and right images delivered alternately. This
would double the frame rate required in order to prevent flickering artifacts.
16.5.3.3 Mono Soundtrack
Simple presentations might only require a monaural
sound track, although it is commonplace to put the same mix on both the left and the right
stereo channel.
16.5.3.4 Stereo Soundtrack
A stereo soundtrack includes both left and right
audio. This is probably the most common format for audio storage alongside the video.
During playback and editing, the two must be totally synchronous with one another.
Editing software must make a frame-accurate cut, but this might happen at an inoppor-
tune time in the audio. Audio and video may be edited independently and any synchro-
nization or tracking problems are fixed later. Editors such as Final Cut Pro take account of
this and maintain good synchronization even when you are performing complex edits.
16.5.3.5 Surround Sound
Dolby 5.1, DTS, and AC3 formats are all varieties of the
surround-sound format. Some of these are coded as interleaved audio with the data being
stored in one single track, and during production the tracks might be held as separate
mono streams so that they can be worked on separately.
16.5.3.6 Audio Description Track
Broadcast regulatory bodies require that televi-
sion companies deliver enhanced services to facilitate access by disabled viewers and lis-
teners. An audio description track is an extra commentary that can be played alongside
the normal audio and contains a description of what is being shown in the video. It is not
a director's commentary, as you would find on a DVD, but it is a similar idea. The track
must be carefully synchronized to ensure that the descriptions are placed between the spo-
ken dialogue and don't obscure what is being said.
16.5.3.7 Structured Audio Track
Structured audio is something that has been
introduced with MPEG-4. It allows for sound samples to be delivered to the player and
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