user1950: I've got a 16:9 standard-def movie into which I need to burn some subtitles. I'm using
 ffmpeg -y -i input.mov -vf ass="./captions.ass" output.mov

and in the subtitle.ass file I've tried
PlayResX: 1024
PlayResY: 576

and
PlayResX: 768
PlayResY: 576

But in both cases the subtitles came out stretched. Is there anything I can do to get them square—either with the ffmpeg command or the subtitle file? I'd rather not stretch the video twice, it's already looking a bit shabby.
Command and console output:
PS C:\Users\stib\Desktop> ffmpeg -i .\test.mov -vf "ass='./test_subs.ass'" test_out.mp4
ffmpeg version N-76144-ge91cd8a Copyright (c) 2000-2015 the FFmpeg developers
  built with gcc 5.2.0 (GCC)
  configuration: --enable-gpl --enable-version3 --disable-w32threads --enable-avisynth --enable-bzlib --enable-fontconfig --enable-frei0r --enable-gnutls --enable-iconv --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-libdcadec --enable-libfreetype --enable-libgme --enable-libgsm --enable-libilbc --enable-libmodplug --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-libopus --enable-librtmp --enable-libschroedinger --enable-libsoxr --enable-libspeex --enable-libtheora --enable-libtwolame --enable-libvidstab --enable-libvo-aacenc --enable-libvo-amrwbenc --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxavs --enable-libxvid --enable-lzma --enable-decklink --enable-zlib
  libavutil      55.  4.100 / 55.  4.100
  libavcodec     57.  7.100 / 57.  7.100
  libavformat    57.  8.102 / 57.  8.102
  libavdevice    57.  0.100 / 57.  0.100
  libavfilter     6. 12.100 /  6. 12.100
  libswscale      4.  0.100 /  4.  0.100
  libswresample   2.  0.100 /  2.  0.100
  libpostproc    54.  0.100 / 54.  0.100
Guessed Channel Layout for  Input Stream #0.1 : stereo
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from '.\test.mov':
  Metadata:
    major_brand     : qt
    minor_version   : 537199360
    compatible_brands: qt
    creation_time   : 2014-05-07 03:24:23
  Duration: 00:01:50.84, start: 0.000000, bitrate: 30340 kb/s
    Stream #0:0(eng): Video: dvvideo (dvcp / 0x70637664), yuv420p(bt470bg/smpte170m/bt709), 720x576 [SAR 64:45 DAR 16:9], 28800 kb/s, SAR 118:81 DAR 295:162, 25 fps, 25 tbr, 25 tbn, 25 tbc (default)
    Metadata:
      creation_time   : 2014-05-07 03:24:23
      handler_name    : Apple Alias Data Handler
      encoder         : DV - PAL
      timecode        : 01:00:00:00
    Stream #0:1(eng): Audio: pcm_s16le (sowt / 0x74776F73), 48000 Hz, 2 channels, s16, 1536 kb/s (default)
    Metadata:
      creation_time   : 2014-05-07 03:24:23
      handler_name    : Apple Alias Data Handler
    Stream #0:2(eng): Data: none (tmcd / 0x64636D74) (default)
    Metadata:
      creation_time   : 2014-05-07 03:24:34
      handler_name    : Apple Alias Data Handler
      timecode        : 01:00:00:00
[Parsed_ass_0 @ 0000000002f61880] Shaper: FriBidi 0.19.6 (SIMPLE)
[Parsed_ass_0 @ 0000000002f61880] Using font provider directwrite
[Parsed_ass_0 @ 0000000002f61880] Added subtitle file: './test_subs.ass' (2 styles, 34 events)
[libx264 @ 0000000002f50cc0] using SAR=118/81
[libx264 @ 0000000002f50cc0] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2 AVX
[libx264 @ 0000000002f50cc0] profile High, level 3.0
[libx264 @ 0000000002f50cc0] 264 - core 148 r2638 7599210 - H.264/MPEG-4 AVC codec - Copyleft 2003-2015 - 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=18 lookahead_threads=3 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=25 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, mp4, to 'test_out.mp4':
  Metadata:
    major_brand     : qt
    minor_version   : 537199360
    compatible_brands: qt
    encoder         : Lavf57.8.102
    Stream #0:0(eng): Video: h264 (libx264) ([33][0][0][0] / 0x0021), yuv420p, 720x576 [SAR 118:81 DAR 295:162], q=-1--1, 25 fps, 12800 tbn, 25 tbc (default)
    Metadata:
      creation_time   : 2014-05-07 03:24:23
      handler_name    : Apple Alias Data Handler
      timecode        : 01:00:00:00
      encoder         : Lavc57.7.100 libx264
    Stream #0:1(eng): Audio: aac (libvo_aacenc) ([64][0][0][0] / 0x0040), 48000 Hz, stereo, s16, 128 kb/s (default)
    Metadata:
      creation_time   : 2014-05-07 03:24:23
      handler_name    : Apple Alias Data Handler
      encoder         : Lavc57.7.100 libvo_aacenc
Stream mapping:
  Stream #0:0 -> #0:0 (dvvideo (native) -> h264 (libx264))
  Stream #0:1 -> #0:1 (pcm_s16le (native) -> aac (libvo_aacenc))
Press [q] to stop, [?] for help
[Parsed_ass_0 @ 0000000002f61880] fontselect: (Univers Com 55 Roman, 400, 0) -> UniversCom-55Roman, 0, UniversCom-55Roman
frame= 2771 fps=345 q=-1.0 Lsize=    8949kB time=00:01:50.85 bitrate= 661.3kbits/s
video:7133kB audio:1733kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.944520%
[libx264 @ 0000000002f50cc0] frame I:12    Avg QP:20.94  size: 50712
[libx264 @ 0000000002f50cc0] frame P:789   Avg QP:23.41  size:  6548
[libx264 @ 0000000002f50cc0] frame B:1970  Avg QP:26.27  size:   776
[libx264 @ 0000000002f50cc0] consecutive B-frames:  1.3%  5.5% 19.1% 74.2%
[libx264 @ 0000000002f50cc0] mb I  I16..4: 13.0% 72.4% 14.6%
[libx264 @ 0000000002f50cc0] mb P  I16..4:  1.0%  2.2%  0.4%  P16..4: 31.9%  9.3%  7.5%  0.0%  0.0%    skip:47.7%
[libx264 @ 0000000002f50cc0] mb B  I16..4:  0.0%  0.1%  0.0%  B16..8: 21.4%  0.9%  0.2%  direct: 0.4%  skip:76.9%  L0:41.3% L1:54.7% BI: 4.0%
[libx264 @ 0000000002f50cc0] 8x8 transform intra:64.5% inter:75.4%
[libx264 @ 0000000002f50cc0] coded y,uvDC,uvAC intra: 66.4% 69.9% 34.2% inter: 5.9% 10.1% 0.9%
[libx264 @ 0000000002f50cc0] i16 v,h,dc,p: 18% 65%  3% 14%
[libx264 @ 0000000002f50cc0] i8 v,h,dc,ddl,ddr,vr,hd,vl,hu: 31% 18% 22%  4%  4%  6%  4%  5%  6%
[libx264 @ 0000000002f50cc0] i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 31% 26% 11%  4%  5%  8%  5%  5%  5%
[libx264 @ 0000000002f50cc0] i8c dc,h,v,p: 42% 25% 28%  5%
[libx264 @ 0000000002f50cc0] Weighted P-Frames: Y:2.3% UV:2.3%
[libx264 @ 0000000002f50cc0] ref P L0: 55.6% 13.1% 21.8%  9.5%  0.0%
[libx264 @ 0000000002f50cc0] ref B L0: 82.5% 13.7%  3.8%
[libx264 @ 0000000002f50cc0] ref B L1: 92.9%  7.1%
[libx264 @ 0000000002f50cc0] kb/s:527.13

ASS file:
[Script Info]
ScriptType: v4.00+
PlayResX: 1024
PlayResY: 576

[V4+ Styles]
Format: Name, Fontname, Fontsize, PrimaryColour, SecondaryColour, OutlineColour, BackColour, Bold, Italic, Underline, BorderStyle, Outline, Shadow, Alignment, MarginL, Margi nR, MarginV, AlphaLevel, Encoding
Style: Default,Univers Com 55 Roman,36,&Hffffff,&Hffffff,&H0,&H0,0,0,0,1,2,0,2,10,10,16,0,0

[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:00.54,0:00:04.70,Default,,0,0,0,,Lorem ipsum dolor sit amet,\Nconsectetur adipiscing
Dialogue: 0,0:00:04.70,0:00:06.96,Default,,0,0,0,,Lorem ipsum dolor sit amet,\Nconsectetur adipiscing
Dialogue: 0,0:00:06.96,0:00:11.78,Default,,0,0,0,,Lorem ipsum dolor sit amet,\Nconsectetur adipiscing
Dialogue: 0,0:00:11.78,0:00:14.81,Default,,0,0,0,,Lorem ipsum dolor sit amet,\Nconsectetur adipiscing
Dialogue: 0,0:00:14.81,0:00:17.39,Default,,0,0,0,,Lorem ipsum dolor sit amet,\Nconsectetur adipiscing
Dialogue: 0,0:00:17.39,0:00:20.60,Default,,0,0,0,,Lorem ipsum dolor sit amet,\Nconsectetur adipiscing
Dialogue: 0,0:00:20.60,0:00:25.22,Default,,0,0,0,,Lorem ipsum dolor sit amet,\Nconsectetur adipiscing
Dialogue: 0,0:00:25.22,0:00:30.31,Default,,0,0,0,,Lorem ipsum dolor sit amet,\Nconsectetur adipiscing
Dialogue: 0,0:00:30.31,0:00:34.48,Default,,0,0,0,,Lorem ipsum dolor sit amet,\Nconsectetur adipiscing
Dialogue: 0,0:00:34.48,0:00:37.11,Default,,0,0,0,,Lorem ipsum dolor sit amet,\Nconsectetur adipiscing
Dialogue: 0,0:00:37.11,0:00:41.28,Default,,0,0,0,,Lorem ipsum dolor sit amet,\Nconsectetur adipiscing
Dialogue: 0,0:00:41.28,0:00:45.14,Default,,0,0,0,,Lorem ipsum dolor sit amet,\Nconsectetur adipiscing
Dialogue: 0,0:00:45.14,0:00:49.98,Default,,0,0,0,,Lorem ipsum dolor sit amet,\Nconsectetur adipiscing
Dialogue: 0,0:00:49.98,0:00:53.79,Default,,0,0,0,,Lorem ipsum dolor sit amet,\Nconsectetur adipiscing
Dialogue: 0,0:00:53.79,0:00:54.97,Default,,0,0,0,,Lorem ipsum dolor sit amet,\Nconsectetur adipiscing
Dialogue: 0,0:00:54.97,0:00:58.59,Default,,0,0,0,,Lorem ipsum dolor sit amet,\Nconsectetur adipiscing
Dialogue: 0,0:00:58.59,0:01:01.88,Default,,0,0,0,,Lorem ipsum dolor sit amet,\Nconsectetur adipiscing
Dialogue: 0,0:01:01.88,0:01:05.73,Default,,0,0,0,,Lorem ipsum dolor sit amet,\Nconsectetur adipiscing
Dialogue: 0,0:01:05.73,0:01:07.95,Default,,0,0,0,,Lorem ipsum dolor sit amet,\Nconsectetur adipiscing
Dialogue: 0,0:01:07.95,0:01:10.56,Default,,0,0,0,,Lorem ipsum dolor sit amet,\Nconsectetur adipiscing
Dialogue: 0,0:01:10.56,0:01:14.00,Default,,0,0,0,,Lorem ipsum dolor sit amet,\Nconsectetur adipiscing
Dialogue: 0,0:01:14.00,0:01:17.27,Default,,0,0,0,,Lorem ipsum dolor sit amet,\Nconsectetur adipiscing
Dialogue: 0,0:01:17.27,0:01:19.99,Default,,0,0,0,,Lorem ipsum dolor sit amet,\Nconsectetur adipiscing
Dialogue: 0,0:01:19.99,0:01:25.51,Default,,0,0,0,,Lorem ipsum dolor sit amet,\Nconsectetur adipiscing
Dialogue: 0,0:01:25.51,0:01:26.48,Default,,0,0,0,,Lorem ipsum dolor sit amet,\Nconsectetur adipiscing
Dialogue: 0,0:01:26.48,0:01:27.45,Default,,0,0,0,,Lorem ipsum dolor sit amet,\Nconsectetur adipiscing
Dialogue: 0,0:01:27.45,0:01:28.80,Default,,0,0,0,,Lorem ipsum dolor sit amet,\Nconsectetur adipiscing
Dialogue: 0,0:01:28.80,0:01:31.37,Default,,0,0,0,,Lorem ipsum dolor sit amet,\Nconsectetur adipiscing
Dialogue: 0,0:01:31.37,0:01:31.92,Default,,0,0,0,,Lorem ipsum dolor sit amet,\Nconsectetur adipiscing
Dialogue: 0,0:01:31.92,0:01:35.05,Default,,0,0,0,,Lorem ipsum dolor sit amet,\Nconsectetur adipiscing
Dialogue: 0,0:01:35.05,0:01:39.18,Default,,0,0,0,,Lorem ipsum dolor sit amet,\Nconsectetur adipiscing
Dialogue: 0,0:01:39.18,0:01:42.72,Default,,0,0,0,,Lorem ipsum dolor sit amet,\Nconsectetur adipiscing
Dialogue: 0,0:01:42.72,0:01:46.37,Default,,0,0,0,,Lorem ipsum dolor sit amet,\Nconsectetur adipiscing
Dialogue: 0,0:01:46.37,0:01:51.25,Default,,0,0,0,,Lorem ipsum dolor sit amet,\Nconsectetur adipiscing


user1871: I found some ASS files, like this sample, which contain a Video Aspect Ratio tag but it seems to not make a difference in ffmpeg hardcoding.
The workaround I can think of right now is to create a complex filter where you create a transparent RGBA canvas of 1024x576; burn the subtitles onto them, scale the result to 768x576 or 720x576, depending on your source video and then overlay that output onto your video.

user1760: You can try adding the original_size filter option, such as:
-vf "ass=test_subs.ass:original_size=768x576"


Specify the size of the original video, the video for which the ASS
  file was composed. For the syntax of this option, check the
  Video size section in the ffmpeg-utils manual. Due to
  a misdesign in ASS aspect ratio arithmetic, this is necessary to
  correctly scale the fonts if the aspect ratio has been changed.


1950: <p>I've got a 16:9 standard-def movie into which I need to burn some subtitles. I'm using</p>

<pre><code> ffmpeg -y -i input.mov -vf ass="./captions.ass" output.mov
</code></pre>

<p>and in the subtitle.ass file I've tried</p>

<pre><code>PlayResX: 1024
PlayResY: 576
</code></pre>

<p>and</p>

<pre><code>PlayResX: 768
PlayResY: 576
</code></pre>

<p>But in both cases the subtitles came out stretched. Is there anything I can do to get them square—either with the ffmpeg command or the subtitle file? I'd rather not stretch the video twice, it's already looking a bit shabby.</p>

<p>Command and console output:</p>

<pre><code>PS C:\Users\stib\Desktop&gt; ffmpeg -i .\test.mov -vf "ass='./test_subs.ass'" test_out.mp4
ffmpeg version N-76144-ge91cd8a Copyright (c) 2000-2015 the FFmpeg developers
  built with gcc 5.2.0 (GCC)
  configuration: --enable-gpl --enable-version3 --disable-w32threads --enable-avisynth --enable-bzlib --enable-fontconfig --enable-frei0r --enable-gnutls --enable-iconv --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-libdcadec --enable-libfreetype --enable-libgme --enable-libgsm --enable-libilbc --enable-libmodplug --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-libopus --enable-librtmp --enable-libschroedinger --enable-libsoxr --enable-libspeex --enable-libtheora --enable-libtwolame --enable-libvidstab --enable-libvo-aacenc --enable-libvo-amrwbenc --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxavs --enable-libxvid --enable-lzma --enable-decklink --enable-zlib
  libavutil      55.  4.100 / 55.  4.100
  libavcodec     57.  7.100 / 57.  7.100
  libavformat    57.  8.102 / 57.  8.102
  libavdevice    57.  0.100 / 57.  0.100
  libavfilter     6. 12.100 /  6. 12.100
  libswscale      4.  0.100 /  4.  0.100
  libswresample   2.  0.100 /  2.  0.100
  libpostproc    54.  0.100 / 54.  0.100
Guessed Channel Layout for  Input Stream #0.1 : stereo
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from '.\test.mov':
  Metadata:
    major_brand     : qt
    minor_version   : 537199360
    compatible_brands: qt
    creation_time   : 2014-05-07 03:24:23
  Duration: 00:01:50.84, start: 0.000000, bitrate: 30340 kb/s
    Stream #0:0(eng): Video: dvvideo (dvcp / 0x70637664), yuv420p(bt470bg/smpte170m/bt709), 720x576 [SAR 64:45 DAR 16:9], 28800 kb/s, SAR 118:81 DAR 295:162, 25 fps, 25 tbr, 25 tbn, 25 tbc (default)
    Metadata:
      creation_time   : 2014-05-07 03:24:23
      handler_name    : Apple Alias Data Handler
      encoder         : DV - PAL
      timecode        : 01:00:00:00
    Stream #0:1(eng): Audio: pcm_s16le (sowt / 0x74776F73), 48000 Hz, 2 channels, s16, 1536 kb/s (default)
    Metadata:
      creation_time   : 2014-05-07 03:24:23
      handler_name    : Apple Alias Data Handler
    Stream #0:2(eng): Data: none (tmcd / 0x64636D74) (default)
    Metadata:
      creation_time   : 2014-05-07 03:24:34
      handler_name    : Apple Alias Data Handler
      timecode        : 01:00:00:00
[Parsed_ass_0 @ 0000000002f61880] Shaper: FriBidi 0.19.6 (SIMPLE)
[Parsed_ass_0 @ 0000000002f61880] Using font provider directwrite
[Parsed_ass_0 @ 0000000002f61880] Added subtitle file: './test_subs.ass' (2 styles, 34 events)
[libx264 @ 0000000002f50cc0] using SAR=118/81
[libx264 @ 0000000002f50cc0] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2 AVX
[libx264 @ 0000000002f50cc0] profile High, level 3.0
[libx264 @ 0000000002f50cc0] 264 - core 148 r2638 7599210 - H.264/MPEG-4 AVC codec - Copyleft 2003-2015 - 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=18 lookahead_threads=3 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=25 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, mp4, to 'test_out.mp4':
  Metadata:
    major_brand     : qt
    minor_version   : 537199360
    compatible_brands: qt
    encoder         : Lavf57.8.102
    Stream #0:0(eng): Video: h264 (libx264) ([33][0][0][0] / 0x0021), yuv420p, 720x576 [SAR 118:81 DAR 295:162], q=-1--1, 25 fps, 12800 tbn, 25 tbc (default)
    Metadata:
      creation_time   : 2014-05-07 03:24:23
      handler_name    : Apple Alias Data Handler
      timecode        : 01:00:00:00
      encoder         : Lavc57.7.100 libx264
    Stream #0:1(eng): Audio: aac (libvo_aacenc) ([64][0][0][0] / 0x0040), 48000 Hz, stereo, s16, 128 kb/s (default)
    Metadata:
      creation_time   : 2014-05-07 03:24:23
      handler_name    : Apple Alias Data Handler
      encoder         : Lavc57.7.100 libvo_aacenc
Stream mapping:
  Stream #0:0 -&gt; #0:0 (dvvideo (native) -&gt; h264 (libx264))
  Stream #0:1 -&gt; #0:1 (pcm_s16le (native) -&gt; aac (libvo_aacenc))
Press [q] to stop, [?] for help
[Parsed_ass_0 @ 0000000002f61880] fontselect: (Univers Com 55 Roman, 400, 0) -&gt; UniversCom-55Roman, 0, UniversCom-55Roman
frame= 2771 fps=345 q=-1.0 Lsize=    8949kB time=00:01:50.85 bitrate= 661.3kbits/s
video:7133kB audio:1733kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.944520%
[libx264 @ 0000000002f50cc0] frame I:12    Avg QP:20.94  size: 50712
[libx264 @ 0000000002f50cc0] frame P:789   Avg QP:23.41  size:  6548
[libx264 @ 0000000002f50cc0] frame B:1970  Avg QP:26.27  size:   776
[libx264 @ 0000000002f50cc0] consecutive B-frames:  1.3%  5.5% 19.1% 74.2%
[libx264 @ 0000000002f50cc0] mb I  I16..4: 13.0% 72.4% 14.6%
[libx264 @ 0000000002f50cc0] mb P  I16..4:  1.0%  2.2%  0.4%  P16..4: 31.9%  9.3%  7.5%  0.0%  0.0%    skip:47.7%
[libx264 @ 0000000002f50cc0] mb B  I16..4:  0.0%  0.1%  0.0%  B16..8: 21.4%  0.9%  0.2%  direct: 0.4%  skip:76.9%  L0:41.3% L1:54.7% BI: 4.0%
[libx264 @ 0000000002f50cc0] 8x8 transform intra:64.5% inter:75.4%
[libx264 @ 0000000002f50cc0] coded y,uvDC,uvAC intra: 66.4% 69.9% 34.2% inter: 5.9% 10.1% 0.9%
[libx264 @ 0000000002f50cc0] i16 v,h,dc,p: 18% 65%  3% 14%
[libx264 @ 0000000002f50cc0] i8 v,h,dc,ddl,ddr,vr,hd,vl,hu: 31% 18% 22%  4%  4%  6%  4%  5%  6%
[libx264 @ 0000000002f50cc0] i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 31% 26% 11%  4%  5%  8%  5%  5%  5%
[libx264 @ 0000000002f50cc0] i8c dc,h,v,p: 42% 25% 28%  5%
[libx264 @ 0000000002f50cc0] Weighted P-Frames: Y:2.3% UV:2.3%
[libx264 @ 0000000002f50cc0] ref P L0: 55.6% 13.1% 21.8%  9.5%  0.0%
[libx264 @ 0000000002f50cc0] ref B L0: 82.5% 13.7%  3.8%
[libx264 @ 0000000002f50cc0] ref B L1: 92.9%  7.1%
[libx264 @ 0000000002f50cc0] kb/s:527.13
</code></pre>

<p>ASS file:</p>

<pre><code>[Script Info]
ScriptType: v4.00+
PlayResX: 1024
PlayResY: 576

[V4+ Styles]
Format: Name, Fontname, Fontsize, PrimaryColour, SecondaryColour, OutlineColour, BackColour, Bold, Italic, Underline, BorderStyle, Outline, Shadow, Alignment, MarginL, Margi nR, MarginV, AlphaLevel, Encoding
Style: Default,Univers Com 55 Roman,36,&amp;Hffffff,&amp;Hffffff,&amp;H0,&amp;H0,0,0,0,1,2,0,2,10,10,16,0,0

[Events]
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</code></pre>
 1871: <p>I found some ASS files, like this <a href="https://code.google.com/p/libass/issues/attachmentText?id=13&amp;aid=130011000&amp;name=sample.ass&amp;token=d55861faec05a2f3cf12b77da74d5505" rel="nofollow">sample</a>, which contain a <code>Video Aspect Ratio</code> tag but it seems to not make a difference in ffmpeg hardcoding.</p>

<p>The workaround I can think of right now is to create a complex filter where you create a transparent RGBA canvas of 1024x576; burn the subtitles onto them, scale the result to 768x576 or 720x576, depending on your source video and then overlay that output onto your video.</p>
 1760: <p>You can try adding the <code>original_size</code> filter option, such as:</p>

<pre><code>-vf "ass=test_subs.ass:original_size=768x576"
</code></pre>

<blockquote>
  <p>Specify the size of the original video, the video for which the ASS
  file was composed. For the syntax of this option, check the
  <a href="https://ffmpeg.org/ffmpeg-utils.html#Video-size" rel="nofollow">Video size section in the ffmpeg-utils manual</a>. Due to
  a misdesign in ASS aspect ratio arithmetic, this is necessary to
  correctly scale the fonts if the aspect ratio has been changed.</p>
</blockquote>
