Based on Georgy's email (
https://www.mail-archive.com/[email protected]/msg09216.html) and
his further explanations, I would like to propose an addition to the manual
regarding an important aspect of CinGG's operation. I am attaching a
document and an image. If you can improve, correct, and add information, we
can then consider modifying the manual.[image: AV_sync.png]
Adjacent Edits in timeline
In \CGG{}, it can happen that two consecutive pieces of footage (edits) in a
video track are not exactly adjacent to each other in timeline, so that in
between there is a tiny (narrower than one single frame) empty segment in the
track where there is no video at all. This happens when the next edit is
attached to the preceding one, in which the lengts of audio (quantified in
units of audio samples, at let's say, 48000 Hz) is slightly more than the
length of video (quantified in frames, at let's say 30 Hz). If this is the
case, \CGG{} can blink with a black frame at this position. See fig ...
The figure shows that edit 2 (audio and video) should be placed next to edit 1
(audio and video) at position A, so that they are adjacent. Instead, edit 2 is
positioned at position C, which is the next frame. This is because the audio 1
samples are longer than determined by the fps of video 1. Edit 2 cannot even be
placed next to position B, i.e., at the end of audio edit 1, because this is
within a single frame and the program only works discretely from frame to frame.
This difference can appear at any stage, reading source, editing/compositing,
rendering the result. The desynchronization can even accumulate and become
worse.
The cause is probably the way in which \CGG{} internally resamples the media to
conform it to the project settings. The source media are allowed to be in
different formats, have different framerates/samplerates from that of the
project. If this is the case, \CGG{} tries to resample them, this is resource
consuming and not very accurate, leading to desync and black blinking frames.
For example, if the source media has VFR (variable frame rate) formats, the
program will definitely perform its own internal resampling. The rendering
phase can also be affected by desync, as can cutting, splicing, and
overwriting. Desync does not always occur (and worse still, propagate during
the editing phases), but if it does occur, the cause is probably internal
resampling. Codecs and formats can also affect desync or the functionality of
\CGG{} for audio/video synchronization via waveform or “GoTo.”
A first solution is to prevent the problem by using source media with settings
identical to those of the project, or transcoded externally to the project
values before being imported into \CGG{}.
If, on the other hand, we notice blinking black frames during editing or in the
final rendering, we must cut away the excess samples from audio edit 1 (A-B
region) to allow for precise alignment of audio/video edits 2 on A point. If
the user sets Settings --> Align cursor on frames in the Program window menu
and manually cuts out this tiny empty segment, two edits segments become
exactly adjacent and black blinking disappears.
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