[Libav-user] transcode.c not working

[Julius Naeumann]

Hi,

I am trying to use the example "transcode.c" example and it isn't working for any file I am feeding it with. 
I am trying to run it on an iPhone using XCode. My FFMPEG version is  3.4.2.
When the function "init_filter" is called for the Video stream, the function avfilter_graph_config will return error -78 : Function not implemented .
The call will also print this message: 
Impossible to convert between the formats supported by the filter 'in' and the filter 'auto_scaler_0'

I have linked against all required libraries: 
AudioToolbox.framework
CoreMedia.framework
VideoToolbox
libiconv
libz
libbz2
( and all of the libav* libraries)

In case anyone needs this, here's info about one of the input files:

Input #0, mov,mp4,m4a,3gp,3g2,mj2, from '/private/var/mobile/Containers/Data/Application/7F65CE6B-F580-40A3-8096-021279F638FF/tmp/6AD45C18-338A-447E-8803-EE8CD92C69C1.MOV':
  Metadata:
    major_brand     : qt  
    minor_version   : 0
    compatible_brands: qt  
    creation_time   : 2018-08-07T14:02:47.000000Z
  Duration: 00:00:06.53, start: 0.000000, bitrate: 4517 kb/s
    Stream #0:0(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, mono, fltp, 63 kb/s (default)
    Metadata:
      creation_time   : 2018-08-07T14:02:47.000000Z
      handler_name    : Core Media Data Handler
    Stream #0:1(und): Video: h264 (High) (avc1 / 0x31637661), yuvj420p(pc, bt709), 1280x720, 4449 kb/s, 26.50 fps, 30 tbr, 600 tbn, 53 tbc (default)
    Metadata:
      rotate          : 90
      creation_time   : 2018-08-07T14:02:47.000000Z
      handler_name    : Core Media Data Handler
      encoder         : H.264
    Side data:
      displaymatrix: rotation of -90.00 degrees

Have I missed something? Can anyone point me into the right direction? Thanks in advance.