• Compression Techniques

  How to convert an image sequence to a PNG encoded MOV with alpha channel

  Posted by Uli Kilian on February 24, 2012 at 3:52 pm

  Hi Guys,

  I’ve searched the whole web and RTFM but couldn’t find an answer to the simple question:
  How can I convert an image sequence with an alpha channel (eg TGA) to a MOV file using the PNG codec while preserving alpha channel.

  I know this is possible because I can export such a MOV out of other software. But I need ffmpeg to do it.

  Again:
  —————–
  What I have:
  32bit TGA files including alpha channel

  What I want:
  A lossless but as small as possible Quicktime file which includes the alpha channel
  —————–

  What I was able to achieve:
  A MOV file holding raw uncompressed data including alpha channel. But that is sometimes 10 times bigger than the (lossless) compressed PNG codec in Quicktime. So I really need it to be smaller. I would be also happy with some other lossless (but compressed) alternative.
  What I used to achieve the uncompressed huge MOV file:

  ffmpeg.exe -r 30 -i C:\temp\test_%04d.tga -y -r 30 -vcodec rawvideo -pix_fmt rgba test.mov

  ffmpeg version N-37208-g01fcbdf Copyright (c) 2000-2012 the FFmpeg developers
built on Jan 27 2012 18:34:52 with gcc 4.6.2
configuration: --enable-gpl --enable-version3 --disable-w32threads --enable-runtime-cpudetect --enable-avisynth --enab
le-bzlib --enable-frei0r --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libfreetype --enable-libgsm --en
able-libmp3lame --enable-libopenjpeg --enable-librtmp --enable-libschroedinger --enable-libspeex --enable-libtheora --en
able-libvo-aacenc --enable-libvo-amrwbenc --enable-libvorbis --enable-libvpx --enable-libx264 --enable-libxavs --enable-
libxvid --enable-zlib
libavutil 51. 34.101 / 51. 34.101
libavcodec 53. 60.100 / 53. 60.100
libavformat 53. 31.100 / 53. 31.100
libavdevice 53. 4.100 / 53. 4.100
libavfilter 2. 60.100 / 2. 60.100
libswscale 2. 1.100 / 2. 1.100
libswresample 0. 6.100 / 0. 6.100
libpostproc 52. 0.100 / 52. 0.100
Input #0, image2, from 'C:\temp\test\nounderscore%04d.tga':
Duration: 00:00:01.03, start: 0.000000, bitrate: N/A
Stream #0:0: Video: targa, bgra, 1920x1080, 30 tbr, 30 tbn, 30 tbc
[buffer @ 01E39C80] w:1920 h:1080 pixfmt:bgra tb:1/1000000 sar:0/1 sws_param:
[buffersink @ 03C302C0] auto-inserting filter 'auto-inserted scale 0' between the filter 'src' and the filter 'out'
[scale @ 03C311E0] w:1920 h:1080 fmt:bgra -> w:1920 h:1080 fmt:rgba flags:0x4
Output #0, mov, to 'nounderscore.mov':
Metadata:
encoder : Lavf53.31.100
Stream #0:0: Video: rawvideo (RGBA / 0x41424752), rgba, 1920x1080, q=2-31, 200 kb/s, 30 tbn, 30 tbc
Stream mapping:
Stream #0:0 -> #0:0 (targa -> rawvideo)
Press [q] to stop, [?] for help
frame= 31 fps= 19 q=0.0 Lsize= 251101kB time=00:00:01.03 bitrate=1990663.1kbits/s
video:251100kB audio:0kB global headers:0kB muxing overhead 0.000325%

  But when I change “-vcode rawvideo” to “-vcode png” it drops the alpha channel alltogether.
  I played around with
  -pix_fmt rgba
  -pix_fmt argb
  -pix_fmt bgra
  -pix_fmt abgr

  but nothing worked…

  On the web there are different solutions but nothing worked for me. It seems my ffmpeg version (which is a fairly new build) doesn’t support it because other people claimed they did it by using exactly the same command.

  Are there any other suggested builds?
  Or am I missing something here?

  Any help is very much appreciated indeed.

  Thanks
  Uli

  Samuel Were replied 13 years, 8 months ago 4 Members · 4 Replies
• 4 Replies

• 

  Reuben Martin

  February 25, 2012 at 2:59 am

  It should work. You might try specifying the input pix_fmt option in front of the -i option to ensure that 32bit mode is enforced.

  You can also try the “qtrle” codec which is basically quicktime animation codec. It supports alpha.
• 

  Uli Kilian

  February 27, 2012 at 7:15 pm

  Reuben – Thanks a lot!
  The qtrle option works. Finally I can encode with alpha channel.
  Thanks for sharing!

  However – as the PNG compression is a bit more efficient it would be nice to get that encoded with ffmpeg.
  If anyone has any idea – please share.
  I tried to put the “-pix_fmt argb” option in front of the -i option – but didn’t make any difference. Nor did all the others (abgr, rgba, etc).

  Anyway.
  Thanks again, Reuben!

  Uli
• 

  Tatiana Solano

  April 23, 2012 at 5:35 pm

  Hello

  I have been working with ffmpeg an a gif animation, so I was trying to do a video from it with alpha channel, and finally with your coments I figure it out, I use a sequence of png images that get from the gif animation and use the next code:

  ffmpeg -i homer%05d.png -vcodec png -pix_fmt rgb32 -y z.mov

  And it works… Hope it helps you
• 

  Samuel Were

  November 1, 2012 at 3:26 pm

  It doesn’t work for me 🙁
  I have mov png with alpha on input and I would like scaled down with alpa on output.
  Everything works OK except output mov has no alpha.
  Please help!

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