vf_drawtext causing font rendering jitter after libharfbuz commit

[Mark Burton]

Summary of the bug:

Prior to the below commit to vf_drawtext, it was possible to draw running timecode, justified to the centre or right edge and not have any horizontal jitter as the numbers ticked up. After the commit, this is no longer the case and the numbers move around horizontally as the width of the characters changes, even though a monospaced font is being used.

avfilter/vf_drawtext: improve glyph shaping and positioning
​https://git.ffmpeg.org/gitweb/ffmpeg.git/commit/1eeb59a2099479eeead8cdc0d4586443fb301a8a

How to reproduce:

% ffmpeg -f lavfi -i "color=black:size=300x100:rate=24" -t 2 -vf "drawtext=fontfile=/Library/Fonts/DroidSansMono.ttf: fontcolor=white: fontsize=40: x=(w-tw)/2: y=(h-th)/2: rate=24: timecode='01\:14\:13\:19'" timecode.mov
ffmpeg version N-111793-gcb1479faca-https://www.martin-riedl.de Copyright (c) 2000-2023 the FFmpeg developers
  built with Apple clang version 14.0.0 (clang-1400.0.29.102)
  configuration: --prefix=/Volumes/ffmpeg_arm64/out --pkg-config-flags=--static --extra-version='https://www.martin-riedl.de' --enable-gray --enable-libxml2 --enable-gpl --enable-libfreetype --enable-fontconfig --enable-libharfbuzz --enable-libbluray --enable-libsnappy --enable-libvmaf --enable-libass --enable-libklvanc --enable-libzimg --enable-libzvbi --enable-libaom --enable-libopenh264 --enable-libopenjpeg --enable-librav1e --enable-libsvtav1 --enable-libvpx --enable-libwebp --enable-libx264 --enable-libx265 --enable-libmp3lame --enable-libopus --enable-libvorbis --enable-libtheora
  libavutil      58. 17.100 / 58. 17.100
  libavcodec     60. 23.100 / 60. 23.100
  libavformat    60. 10.100 / 60. 10.100
  libavdevice    60.  2.101 / 60.  2.101
  libavfilter     9. 11.100 /  9. 11.100
  libswscale      7.  3.100 /  7.  3.100
  libswresample   4. 11.100 /  4. 11.100
  libpostproc    57.  2.100 / 57.  2.100
Input #0, lavfi, from 'color=black:size=300x100:rate=24':
  Duration: N/A, start: 0.000000, bitrate: N/A
  Stream #0:0: Video: wrapped_avframe, yuv420p, 300x100 [SAR 1:1 DAR 3:1], 24 fps, 24 tbr, 24 tbn
Stream mapping:
  Stream #0:0 -> #0:0 (wrapped_avframe (native) -> h264 (libx264))
Press [q] to stop, [?] for help
[libx264 @ 0x1326070e0] using SAR=1/1
[libx264 @ 0x1326070e0] using cpu capabilities: ARMv8 NEON
[libx264 @ 0x1326070e0] profile High, level 1.2, 4:2:0, 8-bit
[libx264 @ 0x1326070e0] 264 - core 164 - H.264/MPEG-4 AVC codec - Copyleft 2003-2023 - http://www.videolan.org/x264.html - options: cabac=1 ref=3 deblock=1:0:0 analyse=0x3:0x113 me=hex subme=7 psy=1 psy_rd=1.00:0.00 mixed_ref=1 me_range=16 chroma_me=1 trellis=1 8x8dct=1 cqm=0 deadzone=21,11 fast_pskip=1 chroma_qp_offset=-2 threads=3 lookahead_threads=1 sliced_threads=0 nr=0 decimate=1 interlaced=0 bluray_compat=0 constrained_intra=0 bframes=3 b_pyramid=2 b_adapt=1 b_bias=0 direct=1 weightb=1 open_gop=0 weightp=2 keyint=250 keyint_min=24 scenecut=40 intra_refresh=0 rc_lookahead=40 rc=crf mbtree=1 crf=23.0 qcomp=0.60 qpmin=0 qpmax=69 qpstep=4 ip_ratio=1.40 aq=1:1.00
Output #0, mov, to 'timecode.mov':
  Metadata:
    encoder         : Lavf60.10.100
  Stream #0:0: Video: h264 (avc1 / 0x31637661), yuv420p(progressive), 300x100 [SAR 1:1 DAR 3:1], q=2-31, 24 fps, 12288 tbn
    Metadata:
      encoder         : Lavc60.23.100 libx264
    Side data:
      cpb: bitrate max/min/avg: 0/0/0 buffer size: 0 vbv_delay: N/A
[out#0/mov @ 0x600003f583c0] video:11kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 12.111263%
frame=   48 fps=0.0 q=-1.0 Lsize=      12kB time=00:00:01.87 bitrate=  52.5kbits/s speed=59.3x    
[libx264 @ 0x1326070e0] frame I:1     Avg QP:12.89  size:  1394
[libx264 @ 0x1326070e0] frame P:14    Avg QP:18.93  size:   239
[libx264 @ 0x1326070e0] frame B:33    Avg QP:25.90  size:   168
[libx264 @ 0x1326070e0] consecutive B-frames:  2.1%  0.0% 56.2% 41.7%
[libx264 @ 0x1326070e0] mb I  I16..4: 68.4%  3.0% 28.6%
[libx264 @ 0x1326070e0] mb P  I16..4:  1.0%  0.3%  1.5%  P16..4:  0.6%  1.5%  1.5%  0.0%  0.0%    skip:93.6%
[libx264 @ 0x1326070e0] mb B  I16..4:  2.9%  0.3%  0.9%  B16..8: 18.4%  2.8%  0.8%  direct: 0.2%  skip:73.6%  L0:31.1% L1:68.4% BI: 0.5%
[libx264 @ 0x1326070e0] 8x8 transform intra:6.8% inter:30.9%
[libx264 @ 0x1326070e0] coded y,uvDC,uvAC intra: 17.4% 0.0% 0.0% inter: 2.4% 0.0% 0.0%
[libx264 @ 0x1326070e0] i16 v,h,dc,p: 81% 11%  8%  0%
[libx264 @ 0x1326070e0] i8 v,h,dc,ddl,ddr,vr,hd,vl,hu: 44% 22% 32%  0%  0%  0%  1%  0%  1%
[libx264 @ 0x1326070e0] i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 44% 10% 22%  6%  3%  2%  3%  7%  2%
[libx264 @ 0x1326070e0] i8c dc,h,v,p: 100%  0%  0%  0%
[libx264 @ 0x1326070e0] Weighted P-Frames: Y:0.0% UV:0.0%
[libx264 @ 0x1326070e0] ref P L0: 66.0%  8.6% 13.1% 12.3%
[libx264 @ 0x1326070e0] ref B L0: 56.9% 41.0%  2.2%
[libx264 @ 0x1326070e0] ref B L1: 98.9%  1.1%
[libx264 @ 0x1326070e0] kb/s:41.16

Patches should be submitted to the ffmpeg-devel mailing list and not this bug tracker.

[Elon Musk]

Fixed in aeff5bcba092583cb85b823bb5dbc14099591408