Image Processing Reference
In-Depth Information
Table 30-9 FFmpeg Components
A command line tool to convert one video file format to another. It also
supports grabbing and encoding in real time from a TV card.
An HTTP multimedia-streaming server for live broadcasts
A simple media player
A library containing all the FFmpeg audio/video encoders and
A library containing parsers and generators for all common
audio/video formats
When digital TV broadcasts are delivered, the audio and video are multiplexed
together, and if you capture and save the transmission in order to keep the footage you just
get one file, an MPEG-2 multiplexed audio and video file. This presents some problems
because you need special tools to unwrap the two streams.
Recording the MPEG-2 multiplex off air with an El-Gato Eye TV gives you this sort
of file. Although this file plays back through QuickTime on a Mac OS system, when you
import the file into Final Cut Pro it separates out the video but loses the audio. This is a
shortcoming of the MPEG-2 codec implementation in QuickTime, and it is unlikely this
will be remedied in the near or distant future.
The solution is to get a copy of the DropDV utility. This will separate the multiplexed
tracks and convert the MPEG-2 into a DV-format file, which is quite a bit larger.
Gamma, Color-Sync, and Video Compression
During a test for this topic, some off-air footage was moved into Final Cut Pro and then
exported as an MPEG-4 file. The MPEG-4 output was virtually identical to the DV copy,
but the conversion from MPEG-2 to the DV format seemed to lose a lot of clarity and
vibrancy. This might have been due to a misinterpretation of some gamma-coding setup.
Either the MPEG-2 player made some compensation that the DV did not, or the gamma
settings got lost along the way. This situation is still being investigated.
Initial research suggests that there is a disjoint in the gamma-correction area. Graphic
arts use Color Sync to adjust colors to a calibrated setting. Historically, QuickTime-based
video compression has ignored Color Sync. Therefore, if you have calibrated your display
and are using a special profile, it does not reflect what happens in the compression system.
Compressors typically use a Generic RGB profile with its inherent gamma setting. So per-
haps it would be a good idea on your compression system to make sure any color calibra-
tion is set to a Generic RGB profile before compressing any video. At least then any
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