[FFmpeg-user] Question for alphamerge

[Paul B Mahol]

On 12/31/12, Johnny <qiangpenggg at gmail.com> wrote:
> Hi,
>
>
> I'm using ffmpeg to produce a video with transparent background, there
> are two videos, one has a pink background and a women walking around,
> and the other is just a white-black luma clip of the first video, i want
> to make the video to be transarent except the women, however, the output
> format is always "Video: vp8, yuv420p", the yuv420p does not support
> alpha channel, but i have no idea how to set the output video pixel
> format, i tried -pix_fmt argb and others, all are failed, please help
> me, thank you very much!
>
> Here is my command:
> $: ffmpeg -i original.webm -vf
> "movie=alpha.webm[alpha];[in][alpha]alphamerge[out]" out.webm

Sorry but, vp8 codec does not support any alpha pixel format, it only
supports yuv420p.

>
> Here is the out put:
> ffmpeg version N-47062-g26c531c Copyright (c) 2000-2012 the FFmpeg
> developers
> built on Nov 25 2012 12:23:20 with gcc 4.7.2 (GCC)
> configuration: --disable-static --enable-shared --enable-gpl
> --enable-version3 --disable-pthreads --enable-runtime-cpudetect --enable-
> ynth --enable-bzlib --enable-frei0r --enable-libass
> --enable-libopencore-amrnb --enable-libopencore-amrwb
> --enable-libfreetype --enable-
> sm --enable-libmp3lame --enable-libnut --enable-libopenjpeg
> --enable-libopus --enable-librtmp --enable-libschroedinger
> --enable-libspeex
> nable-libtheora --enable-libutvideo --enable-libvo-aacenc
> --enable-libvo-amrwbenc --enable-libvorbis --enable-libvpx
> --enable-libx264 --
> le-libxavs --enable-libxvid --enable-zlib
> libavutil 52. 9.100 / 52. 9.100
> libavcodec 54. 77.100 / 54. 77.100
> libavformat 54. 37.100 / 54. 37.100
> libavdevice 54. 3.100 / 54. 3.100
> libavfilter 3. 23.102 / 3. 23.102
> libswscale 2. 1.102 / 2. 1.102
> libswresample 0. 17.101 / 0. 17.101
> libpostproc 52. 2.100 / 52. 2.100
> Input #0, matroska,webm, from 'original.webm':
> Metadata:
> creation_time : 2012-12-14 09:14:51
> Duration: 00:00:38.96, start: 0.000000, bitrate: 1515 kb/s
> Stream #0:0(eng): Video: vp8, yuv420p, 800x1280, SAR 1:1 DAR 5:8, 25
> fps, 25 tbr, 1k tbn, 1k tbc (default)
> [libvpx @ 00bf8980] v1.1.0
> Output #0, webm, to 'out.webm':
> Metadata:
> encoder : Lavf54.37.100
> Stream #0:0(eng): Video: vp8, yuv420p, 800x1280 [SAR 1:1 DAR 5:8],
> q=-1--1, 200 kb/s, 1k tbn, 25 tbc (default)
> Stream mapping:
> Stream #0:0 -> #0:0 (vp8 -> libvpx)
> Press [q] to stop, [?] for help
> frame= 974 fps=7.8 q=0.0 Lsize= 1025kB time=00:00:38.96 bitrate=
> 215.5kbits/s
> video:1018kB audio:0kB subtitle:0 global headers:0kB muxing overhead
> 0.725502%
>
>
> Best Regards & many thanks!
> Johnny
>
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