[FFmpeg-user] Turning an image set into an FLV with transparent background

[Adam]

I have an image set (over 900 PNGs) that I want to merge into FLV.
I've been searching on Google and other places and the best result I got is
a working movie, with a black background.

The command I've been trying:
avconv -r 24 -i HippoBingo_B_Render_%04d.png -i music.wav -r 24 -ac 1
-vcodec flv -strict experimental -s 256x384 -ab 128k z.flv

console output:

adam at ubuntu:~/render$ avconv -r 24 -i HippoBingo_B_Render_%04d.png -i
music.wav -r 24 -ac 1 -vcodec flv -strict experimental -s 256x384 -ab 128k
z.flv
avconv version 0.8.6-6:0.8.6-1ubuntu2, Copyright (c) 2000-2013 the Libav
developers
  built on Mar 30 2013 22:20:06 with gcc 4.7.2
Input #0, image2, from 'HippoBingo_B_Render_%04d.png':
  Duration: 00:00:34.16, start: 0.000000, bitrate: N/A
    Stream #0.0: Video: png, bgra, 400x600, 24 fps, 24 tbr, 24 tbn, 24 tbc
[wav @ 0x1ba8840] max_analyze_duration reached
Input #1, wav, from 'music.wav':
  Duration: 00:00:32.66, bitrate: 1412 kb/s
    Stream #1.0: Audio: pcm_s16le, 44100 Hz, 2 channels, s16, 1411 kb/s
File 'z.flv' already exists. Overwrite ? [y/N] y
Incompatible pixel format 'bgra' for codec 'flv', auto-selecting format
'yuv420p'
[buffer @ 0x21091a0] w:400 h:600 pixfmt:bgra
[scale @ 0x211fda0] w:400 h:600 fmt:bgra -> w:256 h:384 fmt:yuv420p
flags:0x4
Output #0, flv, to 'z.flv':
  Metadata:
    encoder         : Lavf53.21.1
    Stream #0.0: Video: flv, yuv420p, 256x384, q=2-31, 200 kb/s, 1k tbn, 24
tbc
    Stream #0.1: Audio: adpcm_swf, 44100 Hz, 1 channels, s16, 176 kb/s
Stream mapping:
  Stream #0:0 -> #0:0 (png -> flv)
  Stream #1:0 -> #0:1 (pcm_s16le -> adpcm_swf)
Press ctrl-c to stop encoding
frame=  820 fps=198 q=2.0 Lsize=    1776kB time=32.69 bitrate= 445.1kbits/s

video:1046kB audio:706kB global headers:0kB muxing overhead 1.376779%
adam at ubuntu:~/render$ avconv -r 24 -i HippoBingo_B_Render_%04d.png -i
music.wav -r 24 -ac 1 -vcodec flv -strict experimental -s 256x384 -ab 128k
z.flv
avconv version 0.8.6-6:0.8.6-1ubuntu2, Copyright (c) 2000-2013 the Libav
developers
  built on Mar 30 2013 22:20:06 with gcc 4.7.2
Input #0, image2, from 'HippoBingo_B_Render_%04d.png':
  Duration: 00:00:34.16, start: 0.000000, bitrate: N/A
    Stream #0.0: Video: png, bgra, 400x600, 24 fps, 24 tbr, 24 tbn, 24 tbc
[wav @ 0x1ba8840] max_analyze_duration reached
Input #1, wav, from 'music.wav':
  Duration: 00:00:32.66, bitrate: 1412 kb/s
    Stream #1.0: Audio: pcm_s16le, 44100 Hz, 2 channels, s16, 1411 kb/s
File 'z.flv' already exists. Overwrite ? [y/N] y
Incompatible pixel format 'bgra' for codec 'flv', auto-selecting format
'yuv420p'
[buffer @ 0x21091a0] w:400 h:600 pixfmt:bgra
[scale @ 0x211fda0] w:400 h:600 fmt:bgra -> w:256 h:384 fmt:yuv420p
flags:0x4
Output #0, flv, to 'z.flv':
  Metadata:
    encoder         : Lavf53.21.1
    Stream #0.0: Video: flv, yuv420p, 256x384, q=2-31, 200 kb/s, 1k tbn, 24
tbc
    Stream #0.1: Audio: adpcm_swf, 44100 Hz, 1 channels, s16, 176 kb/s
Stream mapping:
  Stream #0:0 -> #0:0 (png -> flv)
  Stream #1:0 -> #0:1 (pcm_s16le -> adpcm_swf)
Press ctrl-c to stop encoding
frame=  820 fps=198 q=2.0 Lsize=    1776kB time=32.69 bitrate= 445.1kbits/s

video:1046kB audio:706kB global headers:0kB muxing overhead 1.376779%




Why do I get a black background?


Sincerely,
Adam.