Some of these things are not documented anywhere, even though all FFmpeg components seem to handle alpha sufficiently consistently. --- libavutil/pixdesc.h | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-)
diff --git a/libavutil/pixdesc.h b/libavutil/pixdesc.h index 705377d..9f0f441 100644 --- a/libavutil/pixdesc.h +++ b/libavutil/pixdesc.h @@ -139,8 +139,16 @@ typedef struct AVPixFmtDescriptor { * An example of a pseudo-paletted format is AV_PIX_FMT_GRAY8 */ #define AV_PIX_FMT_FLAG_PSEUDOPAL (1 << 6) + /** - * The pixel format has an alpha channel. + * The pixel format has an alpha channel. This is set on all formats that + * support alpha in some way. Details are explained in the AVPixelFormat + * enum, and are also encoded in the corresponding AVPixFmtDescriptor. + * The alpha is always straight, never pre-multiplied. + * + * If a codec or a filter does not support alpha, it should support the + * alpha-free format variants only, e.g. AV_PIX_FMT_RGB0 instead of + * AV_PIX_FMT_RGBA. */ #define AV_PIX_FMT_FLAG_ALPHA (1 << 7) -- 2.1.4 _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-devel