how to encode .flv with alpha channel?

[Barbara]

Hello, I am trying to make a .flv video with alpha channel, but the BG keeps coming out black.
I was able to get a transparent background with the .webv format, but the machine I will be using this file is very weird and only reads .flv files.

Do I need to add some special code on the "extra parameters..." box to achieve a transparent BG?

Build: ffmpeg-20180522-fe84f70-win64-static

From: quicktime .mov animation codec with alpha to .flv with alpha.

This is the log:

---

starting ffe job on 2020-09-22 @ 23:05:18.941
command-line: D:\Users\Babs\Desktop\FFMPEG\ffmpeg-20180522-fe84f70-win64-static\bin\ffmpeg.exe -i "D:\Users\Babs\Desktop\CA00666_Multitaction video price oil 2.mov" -vcodec flv -an -b:v 4000k -r 30 "D:\Users\Babs\Desktop\FFMPEG\teste4.flv"

ffmpeg version N-91146-gfe84f70819 Copyright (c) 2000-2018 the FFmpeg developers

built with gcc 7.3.0 (GCC)
configuration: --enable-gpl --enable-version3 --enable-sdl2 --enable-bzlib --enable-fontconfig --enable-gnutls --enable-iconv --enable-libass --enable-libbluray --enable-libfreetype --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-libopus --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libtheora --enable-libtwolame --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxml2 --enable-libzimg --enable-lzma --enable-zlib --enable-gmp --enable-libvidstab --enable-libvorbis --enable-libvo-amrwbenc --enable-libmysofa --enable-libspeex --enable-libxvid --enable-libaom --enable-libmfx --enable-amf --enable-ffnvcodec --enable-cuvid --enable-d3d11va --enable-nvenc --enable-nvdec --enable-dxva2 --enable-avisynth
libavutil 56. 18.102 / 56. 18.102
libavcodec 58. 19.102 / 58. 19.102
libavformat 58. 16.100 / 58. 16.100
libavdevice 58. 4.100 / 58. 4.100
libavfilter 7. 24.100 / 7. 24.100
libswscale 5. 2.100 / 5. 2.100
libswresample 3. 2.100 / 3. 2.100
libpostproc 55. 2.100 / 55. 2.100

[mov,mp4,m4a,3gp,3g2,mj2 @ 000001ded6599c80] Referenced QT chapter track not found
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'D:\Users\Babs\Desktop\CA00666_Multitaction video price oil 2.mov':

Metadata:

major_brand : qt
minor_version : 537199360
compatible_brands: qt
creation_time : 2020-09-29T21:42:32.000000Z

Duration: 00:00:39.90, start: 0.000000, bitrate: 547147 kb/s

Stream #0:0(eng): Video: qtrle (rle / 0x20656C72), bgra(progressive), 4350x1920, 546937 kb/s, SAR 1:1 DAR 145:64, 30 fps, 30 tbr, 30 tbn, 30 tbc (default)
Metadata:

creation_time : 2020-09-29T21:42:32.000000Z
handler_name : Apple Alias Data Handler
encoder : Animation
timecode : 00:00:00:01

Stream #0:1(eng): Data: none (tmcd / 0x64636D74) (default)
Metadata:

creation_time : 2020-09-29T21:42:32.000000Z
handler_name : Apple Alias Data Handler
timecode : 00:00:00:01

Stream mapping:

Stream #0:0 -> #0:0 (qtrle (native) -> flv1 (flv))

Press [q] to stop, ? for help
Output #0, flv, to 'D:\Users\Babs\Desktop\FFMPEG\teste4.flv':

Metadata:

major_brand : qt
minor_version : 537199360
compatible_brands: qt
encoder : Lavf58.16.100
Stream #0:0(eng): Video: flv1 (flv) ([2][0][0][0] / 0x0002), yuv420p, 4350x1920 [SAR 1:1 DAR 145:64], q=2-31, 4000 kb/s, 30 fps, 1k tbn, 30 tbc (default)
Metadata:

creation_time : 2020-09-29T21:42:32.000000Z
handler_name : Apple Alias Data Handler
timecode : 00:00:00:01
encoder : Lavc58.19.102 flv

[Carl Eugen Hoyos]

Feel free to reopen if you can provide an flv file with transparency.

[Barbara]

On the LEFT a .mov with alpha convertet to FLV with alpha in After Effects CS6 - On the RIGHT the same .MOV converted to FLV using FFmpeg

[Barbara]

On the LEFT a .mov with alpha convertet to FLV with alpha in After Effects CS6 - On the RIGHT the same .MOV converted to FLV using FFmpeg

[Carl Eugen Hoyos]

Don't hold your breath.

[Marton Balint]

FFmpeg does not even support VP6 encoding, let alone VP6 encoding with alpha channel...

[Barbara]

Oh ok! Thanks for the help guys!