[FFmpeg-devel] Apparently wrong bitdepth set for RGBA PNG in mov

[Robert Krüger]

Hi,

I transcoded an PNG(RGBA)-Mov sample again into PNG(RGBA)-Mov and the
resulting file is displayed as RGBA and when I export a png frame from
the resulting file, transparency is still there. However, when using
the ffmpeg-generated file in Final Cut, transparency is gone (works
with original). Comparing the atom structure I saw that the
ffmpeg-generated file has a depth of 24 in the stsd atom, while the
original file has 32. Changing the value to 32 in the atom makes FCP
work with the file as expected.

When I just remux the file, 32 is preserved.

command line and output:

ffmpeg -i in.mov -vcodec png out.mov
ffmpeg version N-50095-gb9237aa Copyright (c) 2000-2013 the FFmpeg developers
  built on Feb 20 2013 12:09:22 with llvm-gcc 4.2.1 (LLVM build 2336.11.00)
  configuration:
  libavutil      52. 17.102 / 52. 17.102
  libavcodec     54. 92.100 / 54. 92.100
  libavformat    54. 63.100 / 54. 63.100
  libavdevice    54.  3.103 / 54.  3.103
  libavfilter     3. 38.103 /  3. 38.103
  libswscale      2.  2.100 /  2.  2.100
  libswresample   0. 17.102 /  0. 17.102
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'in.mov':
  Metadata:
    major_brand     : qt
    minor_version   : 512
    compatible_brands: qt
    encoder         : Lavf54.63.100
  Duration: 00:00:00.04, start: 0.000000, bitrate: 10307 kb/s
    Stream #0:0(eng): Video: png (png  / 0x20676E70), rgba, 1920x1080
[SAR 1:1 DAR 16:9], 10162 kb/s, 25 fps, 25 tbr, 12800 tbn, 12800 tbc
    Metadata:
      handler_name    : DataHandler
Output #0, mov, to 'out.mov':
  Metadata:
    major_brand     : qt
    minor_version   : 512
    compatible_brands: qt
    encoder         : Lavf54.63.100
    Stream #0:0(eng): Video: png (png  / 0x20676E70), rgba, 1920x1080
[SAR 1:1 DAR 16:9], q=2-31, 200 kb/s, 12800 tbn, 25 tbc
    Metadata:
      handler_name    : DataHandler
Stream mapping:
  Stream #0:0 -> #0:0 (png -> png)
Press [q] to stop, [?] for help
frame=    1 fps=0.0 q=0.0 Lsize=      50kB time=00:00:00.04
bitrate=10307.4kbits/s
video:50kB audio:0kB subtitle:0 global headers:0kB muxing overhead 1.428824%

Do you need a sample?

Regards,

Robert