# Choose FFmpec decoder

**URL:** <https://forum.opencv.org/t/choose-ffmpec-decoder/8358>\
**Category:** C++\
**Tags:** ffmpeg, videoio\
**Created:** [April 10, 2022, 10:38pm UTC](https://forum.opencv.org/t/choose-ffmpec-decoder/8358 "2022-04-10T22:38:33Z")\
**Posts on this page:** 1\
**Showing post:** 6

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**Author:** ![cudawarped](https://avatars.discourse-cdn.com/v4/letter/c/9dc877/32.png) [@cudawarped](https://forum.opencv.org/u/cudawarped)\
**Post date:** [April 12, 2022, 9:08am UTC](https://forum.opencv.org/t/choose-ffmpec-decoder/8358/6 "2022-04-12T09:08:32Z")

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> [@TheEnigmist](#):
>
> So there is some problem either with opencv or ffmpeg.

As stated in your other post

> [@Open Video file (.gif/.mov/.webm) with alpha channel](https://forum.opencv.org/t/open-video-file-gif-mov-webm-with-alpha-channel/8347):
>
> I’m trying to open a video file (.gif / .webm) with alpha channel on it, but always it gives me 3 channels and it displays with a solid background in Qt6. If I open a normal image .png with alpha channel it works correctly. What I’ve done so far is: VideoCapture capture; capture.open(filename, cv::CAP\_FFMPEG); capture.set(cv::CAP\_PROP\_CONVERT\_RGB, false); //to force loading alpha channel frameRate = capture.get(cv::CAP\_PROP\_FPS); capture.get(cv::CAP\_PROP\_CONVERT\_RGB); // gives 0 //in a thread …

the OpenCV FFMpeg backend does not support an alpha channel

> <https://github.com/opencv/opencv/blob/9aa647068b2eba4a34462927b1878353dfd3df69/modules/videoio/src/cap_ffmpeg_impl.hpp#L1598>

Additonaly `CAP_PROP_CONVERT_RGB` doesn’t have any effect in FFMpeg and if it did I assume it would be to convert from BGR to RGB but I may be wrong.

Out of interest why do you need an alpha channel?

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