The pixel format has an alpha channel. This is set on all formats that
support alpha in some way, including AV_PIX_FMT_PAL8. 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.
The pixel format has an alpha channel. This is set on all formats that support alpha in some way, including AV_PIX_FMT_PAL8. 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.