Encoding to mp3 produces a file with audio and video by default

[Carl Eugen Hoyos]

​http://thread.gmane.org/gmane.comp.video.ffmpeg.user/37424
Since 2dfea12, FFmpeg by default creates a video (png) stream when encoding mp3, this causes a severe performance regression because video has to be decoded.

$ ffmpeg -i fate-suite/svq3/Vertical400kbit.sorenson3.mov out.mp3            ffmpeg version N-41284-ge00b2d2 Copyright (c) 2000-2012 the FFmpeg developers
  built on Jun  4 2012 08:52:52 with gcc 4.3.2
  configuration: --cc=/usr/local/gcc-4.3.2/bin/gcc --enable-gpl --enable-libopenjpeg --enable-libvorbis --enable-libspeex --enable-libmp3lame --enable-libtheora --extra-ldflags=-lm --enable-libvpx --enable-libxavs
  libavutil      51. 56.100 / 51. 56.100
  libavcodec     54. 23.100 / 54. 23.100
  libavformat    54.  6.101 / 54.  6.101
  libavdevice    54.  0.100 / 54.  0.100
  libavfilter     2. 78.100 /  2. 78.100
  libswscale      2.  1.100 /  2.  1.100
  libswresample   0. 15.100 /  0. 15.100
  libpostproc    52.  0.100 / 52.  0.100
[mov,mp4,m4a,3gp,3g2,mj2 @ 0x90123c0] max_analyze_duration 5000000 reached at 5000998
Guessed Channel Layout for  Input Stream #0.1 : mono
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'fate-suite/svq3/Vertical400kbit.sorenson3.mov':
  Metadata:
    creation_time   : 2001-03-20 16:17:18
    title           : Vertical Online SV3 Demo
    title-eng       : Vertical Online SV3 Demo
    artist          : Logan Kelsey
    artist-eng      : Logan Kelsey
    copyright       : © Vertical Online 2001
    copyright-eng   : © Vertical Online 2001
    encoder         : Sorenson Video 3
    encoder-eng     : Sorenson Video 3
  Duration: 00:00:43.57, start: 0.000000, bitrate: 580 kb/s
    Stream #0:0(eng): Video: svq3 (SVQ3 / 0x33515653), yuvj420p, 320x240, 391 kb/s, 30.02 fps, 30 tbr, 600 tbn, 600 tbc
    Metadata:
      creation_time   : 2001-03-20 16:17:18
      handler_name    : Apple Alias Data Handler
    Stream #0:1(eng): Audio: adpcm_ima_qt (ima4 / 0x34616D69), 44100 Hz, mono, s16, 176 kb/s
    Metadata:
      creation_time   : 2001-03-20 16:17:18
      handler_name    : Apple Alias Data Handler
[buffer @ 0x900fa20] w:320 h:240 pixfmt:yuvj420p tb:1/600 sar:0/1 sws_param:flags=2
[ffmpeg_buffersink @ 0x900f8e0] No opaque field provided
[format @ 0x900f9e0] auto-inserting filter 'auto-inserted scaler 0' between the filter 'Parsed_null_0' and the filter 'format'
[auto-inserted scaler 0 @ 0x9012280] w:320 h:240 fmt:yuvj420p sar:0/1 -> w:320 h:240 fmt:rgb24 sar:0/1 flags:0x4
Output #0, mp3, to 'out.mp3':
  Metadata:
    TDEN            : 2001-03-20 16:17:18
    TIT2            : Vertical Online SV3 Demo
    title-eng       : Vertical Online SV3 Demo
    TPE1            : Logan Kelsey
    artist-eng      : Logan Kelsey
    TCOP            : © Vertical Online 2001
    copyright-eng   : © Vertical Online 2001
    encoder-eng     : Sorenson Video 3
    TSSE            : Lavf54.6.101
    Stream #0:0(eng): Video: png, rgb24, 320x240, q=2-31, 200 kb/s, 90k tbn, 30 tbc
    Metadata:
      creation_time   : 2001-03-20 16:17:18
      handler_name    : Apple Alias Data Handler
    Stream #0:1(eng): Audio: mp3, 44100 Hz, mono, s16
    Metadata:
      creation_time   : 2001-03-20 16:17:18
      handler_name    : Apple Alias Data Handler
Stream mapping:
  Stream #0:0 -> #0:0 (svq3 -> png)
  Stream #0:1 -> #0:1 (adpcm_ima_qt -> libmp3lame)
Press [q] to stop, [?] for help
Multiple frames in a packet from stream 1
[mp3 @ 0x9018fa0] Got more than one picture in stream 0, ignoring.
frame= 1308 fps= 49 q=0.0 Lsize=     341kB time=00:00:43.57 bitrate=  64.2kbits/s
video:86771kB audio:341kB global headers:0kB muxing overhead -99.608084%
[libmp3lame @ 0x9011780] 1 frames left in que on closing

[Elon Musk]

Video codec can be disabled, but storing image into tags should not be enabled by default....