[FFmpeg-user] Weird results with drawtext

[Michael Koch]

Am 19.09.2021 um 01:08 schrieb Cecil Westerhof via ffmpeg-user:
> Cecil Westerhof via ffmpeg-user <ffmpeg-user at ffmpeg.org> writes:
>
>> I have several of the following (simplified):
>>      drawtext=
>>         enable     = 'between(t, 105, 115)':
>>         text       = 'speaker':
>>         y          = main_h - (text_h * 4),
>>      drawtext=
>>         enable     = 'between(t, 105, 115)':
>>         text       = 'subject':
>>         y          = main_h - (text_h * 2.2),
>>
>> I have been carefully tweaking to get them on the correct place.
>> But when I was satisfied and generated all eight places where I wanted
>> to have them the placement of the speaker and subject text is on
>> different heights. Sometimes one or the other is different, sometimes
>> both and sometimes they are the same.
>>
>> Is this a bug, or am I doing something wrong?
> As Michael Koch said:
>      The content of the variable "text_h" depends on which characters
>      you are printing.
>
> So I changed:
>      drawtext=
>         enable     = 'between(t, 105, 115)':
>         text       = 'speaker':
>         y          = main_h - (text_h * 4),
>      drawtext=
>         enable     = 'between(t, 105, 115)':
>         text       = 'subject':
>         y          = main_h - (text_h * 2.2),
>
> to:
>      drawtext=
>         enable     = 'between(t, 105, 115)':
>         text       = 'speaker':
>         y          = main_h - 200,
>      drawtext=
>         enable     = 'between(t, 105, 115)':
>         text       = 'subject':
>         y          = main_h - 140,
>
> That gives satisfactory results. The only problem is when the font
> size changes. Then I have to remember I need to change these two
> values also. But I do not expect that to happen often, so I can live
> with that.

As a workaround you could define the strings in a subtitle file and burn 
the subtitles into the frames.
See chapters 2.164 and 2.165 in my book:
http://www.astro-electronic.de/FFmpeg_Book.pdf

Michael