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\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}
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