Fix up black-filling logic.

3 files changed, 92 insertions, 0 deletions

diff --git a/doc/design/who_fills_the_gaps.tex b/doc/design/Attic/who_fills_the_gaps.tex
index 00e8ac39f..00e8ac39f 100644
--- a/doc/design/who_fills_the_gaps.tex
+++ b/doc/design/Attic/who_fills_the_gaps.tex
diff --git a/doc/design/gap_filling.tex b/doc/design/gap_filling.tex
new file mode 100644
index 000000000..a6f748748
--- /dev/null
+++ b/doc/design/gap_filling.tex
@@ -0,0 +1,56 @@
+\documentclass{article}
+\renewcommand{\c}[1]{\texttt{#1}}
+\begin{document}
+
+There are two sources of video gaps:
+
+\begin{enumerate}
+\item Discontiguous outputs from \c{FFmpegDecoder} --- it makes sense
+  to fix these when the frame after the gap is seen, as that's the
+  first time we know about the gap.  For example, it emits frame~1
+  then frame~3; when we see 3 we should emit 2 to fill the gap.
+\item Periods where there is no video content --- these could be long,
+  so you can't just wait for the frame after the gap.
+\end{enumerate}
+
+Two solutions suggest themselves for the period of no video content:
+
+\begin{enumerate}
+\item Create `black' \c{Piece}s to act as dummy content and emit black
+  frames as required.
+\item Fix it in \c{Player::pass()}.
+\end{enumerate}
+
+Dummy pieces feels like a nice solution but quite wordy as you need a
+hierarchy of \c{Piece}s with virtual functions and so on.
+
+If we can trust \c{Decoder::position()} we know the earliest time that
+a decoder will emit data when it is next \c{pass()}ed.  If this is
+more than one frame since the last video frame emitted we know we need
+to emit a black frame.  This much seems straightforward.
+
+Things appear to get harder with seeking.  There are two paths here:
+
+\begin{enumerate}
+\item Seeking into the middle of some video content.
+\item Seeking into some empty space.
+\end{enumerate}
+
+and also differences between accurate and inaccurate seek.
+
+Let's take them case-by-case:
+
+\begin{enumerate}
+  \item \emph{Accurate seek into content} --- we should not fill
+    anything since the correct data will be generated, in time, by
+    \c{pass()}.
+  \item \emph{Accurate seek into space} --- we should fill up to the
+    earliest decoder position.
+  \item \emph{Inaccurate seek into content} --- we should not fill
+    anything since \c{pass()} will generate something at some
+    unknown time.
+  \item \emph{Inaccurate seek into space} --- we should fill up to
+    the earliest decoder position from the seek time.
+\end{enumerate}
+
+\end{document}
diff --git a/doc/design/servers_and_ports.tex b/doc/design/servers_and_ports.tex
new file mode 100644
index 000000000..c635b3054
--- /dev/null
+++ b/doc/design/servers_and_ports.tex
@@ -0,0 +1,36 @@
+\documentclass{article}
+\usepackage[usenames]{xcolor}
+\usepackage{listings}
+\title{Servers and ports}
+\author{}
+\date{}
+\begin{document}
+\maketitle
+
+\begin{tabular}{|l|l|l|}
+  \hline
+  \textbf{Port offset} & \textbf{Component} & \textbf{Purpose} \\
+  \hline
+  0 & \texttt{EncodeServer} & Listen for frame encoding requests \\
+  \hline
+  1 & \texttt{EncodeServer} & Listen for \texttt{DCPOMATIC\_HELLO} from masters \\
+  \hline
+  2 & \texttt{EncodeServerFinder} & Listen for replies to \texttt{DCPOMATIC\_HELLO} from servers \\
+  \hline
+  3 & Batch converter & Listen for job requests \\
+  \hline
+\end{tabular}
+
+
+\texttt{EncodeServer} listens on \texttt{server\_port\_base}.
+Receives an XML \texttt{EncodingRequest} and then the video data.
+Sends back the encoded data.
+
+\texttt{EncodeServer} also listens on $\texttt{server\_port\_base} +
+1$.  A main DCP-o-matic instance broadcasts \texttt{DCPOMATIC\_HELLO}
+on this port.  When a server receives this it connects to the main
+DCP-o-matic on $\texttt{server\_port\_base} + 1$ and tells it what it can do.
+
+Batch Converter listens on $\texttt{server\_port\_base} + 2$ for jobs.
+
+\end{document}