#290 closed defect (fixed)
alpha channel not preserved when transcoding
Reported by: | matteosistisette | Owned by: | Michael Niedermayer |
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Priority: | normal | Component: | undetermined |
Version: | unspecified | Keywords: | alpha yuva420 |
Cc: | Blocked By: | ||
Blocking: | Reproduced by developer: | no | |
Analyzed by developer: | no |
Description
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.
Change History (3)
comment:1 by , 14 years ago
Component: | FFmpeg → undetermined |
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Priority: | critical → normal |
comment:2 by , 13 years ago
Resolution: | → worksforme |
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Status: | new → closed |
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?
comment:3 by , 13 years ago
Keywords: | alpha yuva420 added |
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Resolution: | worksforme → fixed |
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.
Did this work in the past?
and full uncut output from ffmpeg and command line used is missing