alpha channel not preserved when transcoding

[matteosistisette]

When transcoding an flv file which has an alpha channel into a video or image file using codecs that support alpha channel (such as h264, or Apple Animation (qtrle), or PNG) the alpha channel is lost and the output video has an opaque background.

An example flv input file with transparency can be downloaded from  http://totalwebvideo.com/pitchalt.flv

It has alpha channel. H264, Apple Animation and PNG all support alpha channel, so if any of these is used as the encoder and if the input video has alpha channel, the alpha channel should be preserved by default when transcoding.

[michael]

Did this work in the past?
and full uncut output from ffmpeg and command line used is missing

[cehoyos]

Both -vcodec qtrle -pix_fmt argb and -vcodec png -pix_fmt rgb32 encode the alpha channel of your sample as expected.

Does libx264 support encoding an alpha channel?

[cehoyos]

The issue - if there ever was one - has been fixed: The output pix_fmt selection for yuva420 input format works now correctly and chooses 32-bit rgb for png and qtrle.