2019-04-17 11:37 GMT+02:00, Simone Donadini <simone.donad...@avolites.com>:
> When opening a media i need to check if the pixel format holds an alpha > channel. > I can check for the alpha flag in the pixel format description, like this: > const AVPixFmtDescriptor *pixDesc = av_pix_fmt_desc_get(pix_format); > bool has_alpha = pixDesc->flags & AV_PIX_FMT_FLAG_ALPHA; > > But i noticed that inside libavutil/pixdesc.c there is a function for > checking for an alpha channel, which is defined like this: > #define pixdesc_has_alpha(pixdesc) ((pixdesc)->nb_components == 2 || > (pixdesc)->nb_components == 4 || (pixdesc)->flags & AV_PIX_FMT_FLAG_PAL) > I understand the use of AV_PIX_FMT_FLAG_PAL as it is an exception, but could > a pixel format with alpha have a number of components different from 2 and > 4? > > So, which one of the two methods is more reliable? For you as a user, only one method exist, the macro is not exported. If you plan to copy the macro: It is not correct as FFmpeg contains several formats with four components where alpha should be ignored, it is meaningless (RGB0 and friends). Carl Eugen _______________________________________________ Libav-user mailing list Libav-user@ffmpeg.org https://ffmpeg.org/mailman/listinfo/libav-user To unsubscribe, visit link above, or email libav-user-requ...@ffmpeg.org with subject "unsubscribe".
