How to see progress with --exec function

[lcartel]

How to see the progress of the conversion when using ffmpeg with --exec option ?

[dstftw]

C:\Dev\youtube-dl\master>py -3.6 .\youtube_dl\__main__.py BaW_jenozKc  --exec "ffmpeg -y -i {} Kc.webm"
[youtube] BaW_jenozKc: Downloading webpage
[youtube] BaW_jenozKc: Downloading video info webpage
[youtube] BaW_jenozKc: Extracting video information
[youtube] BaW_jenozKc: Downloading MPD manifest
WARNING: Requested formats are incompatible for merge and will be merged into mkv.
[download] Destination: youtube-dl test video ''_ä↭𝕐-BaW_jenozKc.f137.mp4
[download] 100% of 2.11MiB in 00:00
[download] Destination: youtube-dl test video ''_ä↭𝕐-BaW_jenozKc.f251.webm
[download] 100% of 186.27KiB in 00:00
[ffmpeg] Merging formats into "youtube-dl test video ''_ä↭𝕐-BaW_jenozKc.mkv"
Deleting original file youtube-dl test video ''_ä↭𝕐-BaW_jenozKc.f137.mp4 (pass -k to keep)
Deleting original file youtube-dl test video ''_ä↭𝕐-BaW_jenozKc.f251.webm (pass -k to keep)
[exec] Executing command: ffmpeg -y -i "youtube-dl test video ''_ä↭𝕐-BaW_jenozKc.mkv" Kc.webm
ffmpeg version N-85653-gb4330a0 Copyright (c) 2000-2017 the FFmpeg developers
  built with gcc 6.3.0 (GCC)
  configuration: --enable-gpl --enable-version3 --enable-cuda --enable-cuvid --enable-d3d11va --enable-dxva2 --enable-libmfx --enable-nvenc --enable-avisynth --enable-bzlib --enable-fontconfig --enable-frei0r --enable-gnutls --enable-iconv --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-libfreetype --enable-libgme --enable-libgsm --enable-libilbc --enable-libmodplug --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenh264 --enable-libopenjpeg --enable-libopus --enable-librtmp --enable-libsnappy --enable-libsoxr --enable-libspeex --enable-libtheora --enable-libtwolame --enable-libvidstab --enable-libvo-amrwbenc --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxavs --enable-libxvid --enable-libzimg --enable-lzma --enable-zlib
  libavutil      55. 61.100 / 55. 61.100
  libavcodec     57. 93.100 / 57. 93.100
  libavformat    57. 72.101 / 57. 72.101
  libavdevice    57.  7.100 / 57.  7.100
  libavfilter     6. 87.100 /  6. 87.100
  libswscale      4.  7.101 /  4.  7.101
  libswresample   2.  8.100 /  2.  8.100
  libpostproc    54.  6.100 / 54.  6.100
Input #0, matroska,webm, from 'youtube-dl test video ''_├дтЖнЁЭХР-BaW_jenozKc.mkv':
  Metadata:
    COMPATIBLE_BRANDS: iso6avc1mp41
    MAJOR_BRAND     : dash
    MINOR_VERSION   : 0
    ENCODER         : Lavf57.72.101
  Duration: 00:00:09.86, start: -0.007000, bitrate: 1945 kb/s
    Stream #0:0: Video: h264 (High), yuv420p(progressive), 1920x1080, 30 fps, 30 tbr, 1k tbn, 60 tbc (default)
    Metadata:
      HANDLER_NAME    : VideoHandler
      DURATION        : 00:00:09.800000000
    Stream #0:1(eng): Audio: opus, 48000 Hz, stereo, fltp (default)
    Metadata:
      DURATION        : 00:00:09.861000000
Stream mapping:
  Stream #0:0 -> #0:0 (h264 (native) -> vp9 (libvpx-vp9))
  Stream #0:1 -> #0:1 (opus (native) -> opus (libopus))
Press [q] to stop, [?] for help
[libopus @ 00000000023492e0] No bit rate set. Defaulting to 96000 bps.
[libvpx-vp9 @ 00000000024469c0] v1.6.1
Output #0, webm, to 'Kc.webm':
  Metadata:
    COMPATIBLE_BRANDS: iso6avc1mp41
    MAJOR_BRAND     : dash
    MINOR_VERSION   : 0
    encoder         : Lavf57.72.101
    Stream #0:0: Video: vp9 (libvpx-vp9), yuv420p, 1920x1080, q=-1--1, 200 kb/s, 30 fps, 1k tbn, 30 tbc (default)
    Metadata:
      HANDLER_NAME    : VideoHandler
      DURATION        : 00:00:09.800000000
      encoder         : Lavc57.93.100 libvpx-vp9
    Side data:
      cpb: bitrate max/min/avg: 0/0/0 buffer size: 0 vbv_delay: -1
    Stream #0:1(eng): Audio: opus (libopus), 48000 Hz, stereo, flt, 96 kb/s (default)
    Metadata:
      DURATION        : 00:00:09.861000000
      encoder         : Lavc57.93.100 libopus
frame=  179 fps=7.2 q=0.0 Lsize=     335kB time=00:00:06.21 bitrate= 441.5kbits/s speed=0.25x
video:264kB audio:67kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 1.173642%
Exiting normally, received signal 2.