Support multiline metadata values parsing in 'ffmpeg_parse_infos'

[mondeja]

From #207, the output reported by the user can't be parsed correctly by FFMpegInfosParser:

  Metadata:
    major_brand     : qt  
    minor_version   : 537199360
    compatible_brands: qt  
    creation_time   : 2015-09-14 14:57:32
    xmp             : <?xpacket begin="" id="W5M0MpCehiHzreSzNTczkc9d"?>
                    : <x:xmpmeta xmlns:x="adobe:ns:meta/" x:xmptk="Adobe XMP Core 5.0-c060 61.136967, 2010/06/15-10:43:27        ">
                    :  <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
                    :   <rdf:Description rdf:about=""
                    :     xmlns:xmpMM="http://ns.adobe.com/xap/1.0/mm/"
                    :     xmlns:xmpDM="http://ns.adobe.com/xmp/1.0/DynamicMedia/"
                    :     xmlns:stDim="http://ns.adobe.com/xap/1.0/sType/Dimensions#"
                    :     xmlns:dc="http://purl.org/dc/elements/1.1/"
                    :    xmpMM:DocumentID="xmp.did:39FA818BE85AE511B9009F953BF804AA"
                    :    xmpMM:InstanceID="xmp.iid:39FA818BE85AE511B9009F953BF804AA"
                    :    xmpDM:videoFrameRate="24.000000"
                    :    xmpDM:videoFieldOrder="Progressive"
                    :    xmpDM:videoPixelAspectRatio="1/1"
                    :    xmpDM:audioSampleRate="44100"
                    :    xmpDM:audioSampleType="16Int"
                    :    xmpDM:audioChannelType="Mono"
                    :    dc:format="QuickTime">
                    :    <xmpDM:startTimecode
                    :     xmpDM:timeValue="00:00:00:00"
                    :     xmpDM:timeFormat="24Timecode"/>
                    :    <xmpDM:altTimecode
                    :     xmpDM:timeValue="00:00:00:00"
                    :     xmpDM:timeFormat="24Timecode"/>
                    :    <xmpDM:videoFrameSize
                    :     stDim:w="768"
                    :     stDim:h="576"
                    :     stDim:unit="pixel"/>
                    :   </rdf:Description>
                    :  </rdf:RDF>
                    : </x:xmpmeta>
                    :                                                                                                     
                    :                                                                                                     
                    :                                                                                                     
                    :                                                                                                     
                    :                                                                                                     
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                    :                                                                                                     
                    :                                                                                                     
                    :                                                                                                     
                    :                            
                    : <?xpacket end="w"?>
  Duration: 00:02:10.67, start: 0.000000, bitrate: 26287 kb/s
    Stream #0:0(eng): Video: mjpeg (jpeg / 0x6765706A), yuvj422p(pc, bt470bg), 768x576 [SAR 72:72 DAR 4:3], 26213 kb/s, 24 fps, 24 tbr, 24 tbn, 24 tbc (default)
    Metadata:
      creation_time   : 2015-09-14 14:57:32
      handler_name    : Gestionnaire d�alias Apple
      encoder         : Photo - JPEG
      timecode        : 00:00:00:00
    Stream #0:1(eng): Audio: aac (mp4a / 0x6134706D), 44100 Hz, mono, fltp, 64 kb/s (default)
    Metadata:
      creation_time   : 2015-09-14 14:57:32
      handler_name    : Gestionnaire d�alias Apple
      timecode        : 00:00:00:00
    Stream #0:2(eng): Data: none (tmcd / 0x64636D74) (default)
    Metadata:
      creation_time   : 2015-09-14 14:58:24
      handler_name    : Gestionnaire d�alias Apple
      timecode        : 00:00:00:00
At least one output file must be specified

XMP fields included currently in the result are:

• xmp -> <?xpacket begin="" id="W5M0MpCehiHzreSzNTczkc9d"?>
• <empty> -> <?xpacket end="w"?>