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| author | Steven Robertson <steven@strobe.cc> | 2012-07-10 22:14:57 -0700 |
|---|---|---|
| committer | Stefano Sabatini <stefasab@gmail.com> | 2012-07-22 12:17:34 +0200 |
| commit | 82ecae8a7069104698d491000b37629cd8d96fd8 (patch) | |
| tree | 90de57d08d4e0c14ff9b05f40172b25255a30392 /doc | |
| parent | 8c2ce16f93be0fc1362ab74846b46c9818da14be (diff) | |
lavfi: add alphaextract and alphamerge filters
These filters are designed for storing and transmitting video sequences
with alpha using higher-efficiency codecs such as x264 which don't
natively support an alpha channel. 'alphaextract' takes an input stream
with an alpha channel and returns a video containing just the alpha
component as a grayscale value; 'alphamerge' takes an RGB or YUV stream
and adds an alpha channel recovered from a second grayscale stream.
Signed-off-by: Steven Robertson <steven@strobe.cc>
Signed-off-by: Stefano Sabatini <stefasab@gmail.com>
Diffstat (limited to 'doc')
| -rw-r--r-- | doc/filters.texi | 25 |
1 files changed, 25 insertions, 0 deletions
diff --git a/doc/filters.texi b/doc/filters.texi index 4a6c092e59..2b5cc875f5 100644 --- a/doc/filters.texi +++ b/doc/filters.texi @@ -1101,6 +1101,31 @@ build. Below is a description of the currently available video filters. +@section alphaextract + +Extract the alpha component from the input as a grayscale video. This +is especially useful with the @var{alphamerge} filter. + +@section alphamerge + +Add or replace the alpha component of the primary input with the +grayscale value of a second input. This is intended for use with +@var{alphaextract} to allow the transmission or storage of frame +sequences that have alpha in a format that doesn't support an alpha +channel. + +For example, to reconstruct full frames from a normal YUV-encoded video +and a separate video created with @var{alphaextract}, you might use: +@example +movie=in_alpha.mkv [alpha]; [in][alpha] alphamerge [out] +@end example + +Since this filter is designed for reconstruction, it operates on frame +sequences without considering timestamps, and terminates when either +input reaches end of stream. This will cause problems if your encoding +pipeline drops frames. If you're trying to apply an image as an +overlay to a video stream, consider the @var{overlay} filter instead. + @section ass Draw ASS (Advanced Substation Alpha) subtitles on top of input video |