\chapter{Project and Media Attributes}%
\label{cha:project_and_media_attributes}
\index{project attributes}
\index{format}
\index{settings}

When you play media files in \CGG{}, the media files have a certain
number of tracks, frame size, sample size, and so on.  No matter
what attributes the media file has, it is played back according to
the project attributes.  So, if an audio file's sample rate is
different than the project attributes, it is resampled.  Similarly,
if a video file's frame size is different than the project
attributes, the video is composited on a black frame, either cropped
or bordered with black.

The project attributes are adjusted in \texttt{Settings $\rightarrow$
Format} (figure~\ref{fig:set-format}) or can be created in
\texttt{File $\rightarrow$ New}.  When you adjust project settings
in \texttt{File $\rightarrow$ New}, a new empty timeline is created.
Every timeline created from this point on uses the same settings.
When you adjust settings in \texttt{Settings $\rightarrow$ Format},
media on the timeline is left unchanged.  But every timeline created
from this point uses the same settings.

\begin{figure}[htpb]\centering
\includegraphics[width=0.6\linewidth]{set-format.png}
  \caption{Set Format window - note the Audio Channel positions}
  \label{fig:set-format}
\end{figure}

In addition to the standard settings for sample rate, frame rate,
and frame size, \CGG{} uses some less traditional settings like
channel positions, color model, and aspect ratio.  The aspect ratio
refers to the screen aspect ratio (SAR).

Edit decision lists , the EDL \index{EDL} stored in XML, save the project
settings.  Formats which contain media but no edit decisions just
add data to the tracks.  Keep in mind details such as if your
project sample rate is 48\,kHz and you load a sound file with
96\,kHz, you will still be playing it at 48\,kHz.  Or if you load an
EDL file at 96\,kHz and the current project sample rate is 48\,kHz,
you will change it to 96\,kHz.

The New Project window has some options that are different than the
Set Format window as you can see by comparing
figure~\ref{fig:set-format} above with this
figure~\ref{fig:new-project}.  Mostly notably is the field for a
directory path and a Project Name.

\begin{figure}[htpb] \centering
\includegraphics[width=0.7\linewidth]{new-project.png}
  \caption{New Project dialog window}
  \label{fig:new-project}
\end{figure}

Explanation of the various fields is described next.

\section{Audio attributes}%
\label{sec:audio_attributes}
\index{audio!attributes}


\begin{description}
\item[Presets:] select an option from this menu to have all the
project settings set to one of the known standards.  Some of the
options are 1080P/24, 1080I, 720P/60, PAL, NTSC, YouTube, and CD
audio.

\item[Tracks:] (in New Project menu only) sets the number of audio
tracks for the new project. Tracks can be added or deleted later,
but this option is on the New Project menu for convenience.

\item[Samplerate:] \index{sample rate} sets the samplerate of the audio. The project
samplerate does not have to be the same as the media sample rate
that you load. Media is resampled to match the project sample rate.

\item[Channels:] \index{audio!channels} sets the number of audio channels for the new
project. The number of audio channels does not have to be the same
as the number of tracks.

\item[Channel positions:] the currently enabled audio channels and
their positions in the audio panning boxes in the track patchbay are
displayed in the channel position widget in the Set Format window.
You can see this display on the left side in
figure~\ref{fig:set-format} above.  Channel positions are not in New
Project window.

  The channels are numbered.  When rendered, the output from channel
1 is rendered to the first output track in the file or the first
sound card channel of the sound card.  Later channels are rendered
to output tracks numbered consecutively.  The audio channel
positions correspond to where in the panning widgets each of the
audio outputs is located.  The closer the panning position is to one
of the audio outputs, the more signal that speaker gets.  Click on a
speaker icon and drag to change the audio channel location.  The
speakers can be in any orientation.  A different speaker arrangement
is stored for every number of audio channels since normally you do
not want the same speaker arrangement for different numbers of
channels.

  Channel positions is the only setting that does not affect the
output necessarily.  It is merely a convenience, so that when more
than two channels are used, the pan controls on the timeline can
distinguish between them.  It has nothing to do with the actual
arrangement of speakers.  Different channels can be positioned very
close together to make them have the same output.
\end{description}


\section{Video attributes}%
\label{sec:video_attributes}
\index{video!attributes}

\begin{description}
\item[Tracks:] (in New Project menu only) sets the number of video
tracks the new project is assigned.  Tracks can be added or deleted
later, but options are provided here for convenience.

\item[Framerate:] \index{framerate} sets the framerate of the video.  The project
framerate does not have to be the same as an individual media file
frame rate that you load.  Media is reframed to match the project
framerate.

\item[Canvas size:] \index{canvas size} sets the size of the video output \index{output size}.  In addition,
each track also has its own frame size.  Initially, the New Project
dialog creates video tracks whose size match the video output.  The
video track sizes can be changed later without changing the video
output.

\item[Aspect ratio:] \index{aspect ratio} sets the aspect ratio; this aspect ratio refers
to the screen aspect ratio.  The aspect ratio is applied to the
video output.  The aspect ratio can be different than the ratio that
results from the formula: $\dfrac{h}{v}$ (the number of horizontal
pixels divided into the number of vertical pixels).  If the aspect
ratio differs from the results of the formula above, your output
will be in non-square pixels.

\item[Auto aspect ratio:] if this option is checked, the Set Format
dialog always recalculates the Aspect ratio setting based upon the
given Canvas size. This ensures pixels are always square.

\item[Color model:] \index{color!model} the internal color space of \CGG{} is X11 sRGB
without color profile. \CGG{} always switches to sRGB when applying
filters or using the compositing engine. Different case for
decoding/playback or encoding/output; the project will be stored in
the color model video that is selected in the dropdown.  Color model
is important for video playback because video has the disadvantage
of being slow compared to audio.  Video is stored on disk in one
colormodel, usually a YUV derivative.  When played back, \CGG{}
decompresses it from the file format directly into the format of the
output device.  If effects are processed, the program decompresses
the video into an intermediate colormodel first and then converts it
to the format of the output device.  The selection of an
intermediate colormodel determines how fast and accurate the effects
are.  A list of the current colormodel choices follows.

  \begin{description}
  \item[RGB-8 bit] Allocates 8\,bits for the R, G, and B channels
and no alpha. This is normally used for uncompressed media with low
dynamic range.
  \item[RGBA-8 bit] Allocates an alpha channel to the 8\,bit RGB
colormodel. It can be used for overlaying multiple tracks.
  \item[RGB-Float] Allocates a 32\,bit float for the R, G, and B
channels and no alpha. This is used for high dynamic range
processing with no transparency.
  \item[RGBA-Float] This adds a 32\,bit float for alpha to
RGB-Float. It is used for high dynamic range processing with
transparency. Or when we don't want to lose data during workflow,
for example in color correction, key extraction and motion
tracking.
  \item[YUV-8 bit] Allocates 8\,bits for Y, U, and V. This is used
for low dynamic range operations in which the media is compressed in
the YUV color space. Most compressed media is in YUV and this
derivative allows video to be processed fast with the least color
degradation.
  \item[YUVA-8 bit] Allocates an alpha channel to the 8\,bit YUV
colormodel for transparency.
  \end{description}

In order to do effects which involve alpha
channels \index{alpha channel}, a colormodel with an alpha channel must be selected.
These are RGBA-8 bit, YUVA-8 bit, and RGBA-Float.  The 4 channel
colormodels are slower than 3\,channel colormodels, with the slowest
being RGBA-Float.  Some effects, like fade, work around the need for
alpha channels while other effects, like chromakey, require an alpha
channel in order to be functional.  So in order to get faster
results, it is always a good idea to try the effect without alpha
channels to see if it works before settling on an alpha channel and
slowing it down.

  When using compressed footage, YUV colormodels \index{yuv} are usually faster
than RGB colormodels \index{RGB}.  They also destroy fewer colors than RGB
colormodels.  If footage stored as JPEG or MPEG is processed many
times in RGB, the colors will fade whereas they will not fade if
processed in YUV\@.  Years of working with high dynamic range footage
has shown floating point RGB to be the best format for high dynamic
range.  16 bit integers were used in the past and were too lossy and
slow for the amount of improvement.  RGB float does not destroy
information when used with YUV source footage and also supports
brightness above 100\,\%.  Be aware that some effects, like
Histogram, still clip above 100\,\% when in floating point. See also \ref{sec:color_space_range_playback} and \ref{sec:conform_the_project}.

\item[Interlace mode:] \index{interlacing} this is mostly obsolete in the modern digital
age, but may be needed for older media such as that from broadcast
TV\@.  Interlacing uses two fields to create a frame. One field
contains all odd-numbered lines in the image; the other contains all
even-numbered lines.  Interlaced fields are stored in alternating
lines of interlaced source footage. The alternating lines missing on
each output frame are interpolated.
\end{description}

\section{Best practice in pre-editing}%
\label{sec:best_practice_pre_editing}

\CGG{} supports the simultaneous presence in the Timeline of sources with different frame sizes and frame rates. However, audio/video synchronization problems may occur due to their different timing.\protect\footnote{credit to sge and Andrew Randrianasulu}
Plugins that rely on the timing of each frame, for example \textit{Motion} and \textit{Interpolate} plugins, may have problems when used at the same time with engines which increase frame rate. Frame rate per definition cannot be increased without either duplicating some frames or generating them in some intelligent way. But to work reliably, the \textit{Motion} plugin requires access to all actual frames. These kinds of plugins (and also the rare cases of audio/video desync) explicitly require the \textit{Play every frame} option.

There is no problem as long as the source fps, project fps, and destination fps are identical. In most cases, high frame rates such as 120 or 144 or any fps, will be just fine for \textit{Motion} provided that source footage all has the same frame rate.

But when \textit{project} and \textit{source} frame rates are different (or \textit{project} and
\textit{rendered} fps), then the \CGG{} engine has to either duplicate (interpolate) some frames or throw some away. Because of this, the audio tracks and the timeline get out of sync with such accelerated (or slowed down) video. And to make \textit{Motion} plugins reliably calculate interframe changes, you have to ensure the consistent frame numbers and frame properties.

Generally, best practice is to perform the following sequence of preparations for video editing.

\begin{enumerate}
	\item Motion stabilization, and maybe some other preparations, to improve the quality of the source video is best done under the properties identical to the properties of the original video; it may be different codec, but same frame size and same frame rate.
	\item If you need to alter the frame rate, for example because different source clips have different frame rates, then recode all the necessary clips to the same future project frame rate. Here frame sizes can still have different sizes, but frame rates should be all the same.
	\item Whole editing: if you need to change frame rate of some restricted part, particularly when smooth acceleration/deceleration is needed, it can be done here. But if frame rate has to be changed only due to different source fps, it is better to do it during the preparation stage.
\end{enumerate}

\CGG{} does not have color management \index{color management}, but we can still give some general advice on how to set color spaces:

\begin{enumerate}
	\item Profiling and setting the monitor: \\
	source: \textit{sRGB} $\rightarrow$ monitor: \textit{sRGB}  (we get a correct color reproduction) \\
	source: \textit{sRGB} $\rightarrow$ monitor: \textit{rec709} (we get slightly dark colors) \\
	source: \textit{sRGB} $\rightarrow$ monitor: \textit{DCI-P3} (we get over-saturated colors) \\
	
	source: \textit{rec709} $\rightarrow$ monitor: \textit{rec709} (we get a correct color reproduction) \\
	source: \textit{rec709} $\rightarrow$ monitor: \textit{sRGB} (we get slightly faded colors) \\
	source: \textit{rec709} $\rightarrow$ monitor: \textit{DCI-P3} (we get over-saturated colors)
	\item It would be better to set the project as RGB(A)-FLOAT, allowing system performance, because it collects all available data and does not make rounding errors. If we can't afford it, starting from YUV type media it is better to set the project as YUV(A)8, so as not to have a darker rendering in the timeline. On the contrary, if we start from RGB signals, it is better to use RGB(A)8. If we don't display correctly on the timeline, we'll make adjustments from the wrong base (metamerism) and get false results.
	\item Having correct color representation in the Compositor can be complicated. You can convert the imput \textit{YUV color range} to a new YUV color range that provides more correct results (i.e. MPEG to JPEG). The \texttt{Colorspace} plugin can be used for this conversion.
	\item Among the rendering options always set the values \\	
	\texttt{color\_trc=...} (gamma correction) \\
	\texttt{color\_primaries=...} (gamut) \\
	\texttt{colorspace=...} (color spaces conversion, more depth-color); \\
	or \\
	\texttt{colormatrix=...} (color spaces conversion, faster).
	
	These are only metadata that do not affect rendering but when the file is read by a player later they are used to reproduce the colors without errors.
\end{enumerate}

For more tips on how \CGG{} processes colors on the timeline see  \nameref{sec:color_space_range_playback} and \nameref{sec:conform_the_project}.

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