diff options
| -rw-r--r-- | libavutil/pixdesc.h | 13 | ||||
| -rw-r--r-- | libavutil/pixfmt.h | 4 |
2 files changed, 14 insertions, 3 deletions
diff --git a/libavutil/pixdesc.h b/libavutil/pixdesc.h index c8e32518a8..c4d0548ad6 100644 --- a/libavutil/pixdesc.h +++ b/libavutil/pixdesc.h @@ -139,8 +139,19 @@ 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. The exception is AV_PIX_FMT_PAL8, which can + * carry alpha as part of the palette. 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 set all alpha to + * opaque, or use the equivalent pixel formats without alpha component, e.g. + * AV_PIX_FMT_RGB0 (or AV_PIX_FMT_RGB24 etc.) instead of AV_PIX_FMT_RGBA. */ #define AV_PIX_FMT_FLAG_ALPHA (1 << 7) diff --git a/libavutil/pixfmt.h b/libavutil/pixfmt.h index 5d443ce9a4..73d4cc987a 100644 --- a/libavutil/pixfmt.h +++ b/libavutil/pixfmt.h @@ -44,11 +44,11 @@ * big-endian CPUs. * * @par - * When the pixel format is palettized RGB (AV_PIX_FMT_PAL8), the palettized + * When the pixel format is palettized RGB32 (AV_PIX_FMT_PAL8), the palettized * image data is stored in AVFrame.data[0]. The palette is transported in * AVFrame.data[1], is 1024 bytes long (256 4-byte entries) and is * formatted the same as in AV_PIX_FMT_RGB32 described above (i.e., it is - * also endian-specific). Note also that the individual RGB palette + * also endian-specific). Note also that the individual RGB32 palette * components stored in AVFrame.data[1] should be in the range 0..255. * This is important as many custom PAL8 video codecs that were designed * to run on the IBM VGA graphics adapter use 6-bit palette components. |