[postprocessor/ffmpeg] Do not copy Apple TV chapter tracks

[Tatsh]

This is a continuation of #15846 since I no longer can write to that fork/branch.

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• At least skimmed through adding new extractor tutorial and youtube-dl coding conventions sections
• Searched the bugtracker for similar pull requests
• Checked the code with flake8

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What is the purpose of your pull request?

• Bug fix
• Improvement
• New extractor
• New feature

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Description of your pull request and other information

Some files coming from YouTube and probably others come with chapter data (or subtitle?) in a stream seen by ffmpeg as the bin_data codec, usually at 0:2. Without some help, ffmpeg will simply refuse to make an mp4 file containing this. This causes the subtitle post-processor to fail, which also stops any further processing (embed thumbnail, etc).

    Stream #0:2(eng): Data: bin_data (text / 0x74786574), 0 kb/s
    Metadata:
      handler_name    : SubtitleHandler

This PR adjusts the subtitle post-processor to 'disable' (but not really) all data streams in the ffmpeg command. The resulting files still end up having the bin_data stream, but the SRT subtitle is now properly embedded before it:

    Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p(tv, bt709), 1920x1080 [SAR 1:1 DAR 16:9], 1234 kb/s, 29.97 fps, 29.97 tbr, 90k tbn, 59.94 tbc (default)
    Metadata:
      handler_name    : VideoHandler
    Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 125 kb/s (default)
    Metadata:
      handler_name    : SoundHandler
    Stream #0:2(eng): Subtitle: mov_text (tx3g / 0x67337874), 0 kb/s (default)
    Metadata:
      handler_name    : SubtitleHandler
    Stream #0:3(eng): Data: bin_data (text / 0x74786574), 0 kb/s
    Metadata:
      handler_name    : SubtitleHandler
    Stream #0:4: Video: mjpeg, yuvj420p(pc, bt470bg/unknown/unknown), 1280x720 [SAR 1:1 DAR 16:9], 90k tbr, 90k tbn, 90k tbc

Example YouTube ID: KaAdS8Oso9U

Related ffmpeg issue

This also disables "Last message repeated" messages which cause non-zero exit status. Most of the time these messages are programmer issues for the ffmpeg team and do not apply to users.