这是一个普遍的问题，但这样的事情存在吗？我将 .ass 全格式字幕刻录到 .mp4 视频中，刻录字幕的质量在输出视频中降低了，例如：文本边框模糊。
我使用的命令：
ffmpeg -i input.mp4 -vf "ass=subtitle.ass" output.mp4
输出：
>ffmpeg -i input.mp4 -vf "ass=subtitle.ass" output.mp4
ffmpeg version N-73010-gbb3703a Copyright (c) 2000-2015 the FFmpeg developers
built with gcc 4.9.2 (GCC)
configuration: --enable-gpl --enable-version3 --disable-w32threads --enable-av
isynth --enable-bzlib --enable-fontconfig --enable-frei0r --enable-gnutls --enab
le-iconv --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --
enable-libdcadec --enable-libfreetype --enable-libgme --enable-libgsm --enable-l
ibilbc --enable-libmodplug --enable-libmp3lame --enable-libopencore-amrnb --enab
le-libopencore-amrwb --enable-libopenjpeg --enable-libopus --enable-librtmp --en
able-libschroedinger --enable-libsoxr --enable-libspeex --enable-libtheora --ena
ble-libtwolame --enable-libvidstab --enable-libvo-aacenc --enable-libvo-amrwbenc
--enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libwebp --enabl
e-libx264 --enable-libx265 --enable-libxavs --enable-libxvid --enable-lzma --ena
ble-decklink --enable-zlib
libavutil 54. 27.100 / 54. 27.100
libavcodec 56. 41.100 / 56. 41.100
libavformat 56. 37.100 / 56. 37.100
libavdevice 56. 4.100 / 56. 4.100
libavfilter 5. 17.100 / 5. 17.100
libswscale 3. 1.101 / 3. 1.101
libswresample 1. 2.100 / 1. 2.100
libpostproc 53. 3.100 / 53. 3.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'input.mp4':
Metadata:
major_brand : isom
minor_version : 512
compatible_brands: isomiso2avc1mp41
encoder : PotEncoder
Duration: 00:01:17.69, start: 0.000000, bitrate: 1159 kb/s
Stream #0:0(und): Video: h264 (Main) (avc1 / 0x31637661), yuv420p, 640x360 [
SAR 1:1 DAR 16:9], 1026 kb/s, 29.97 fps, 29.97 tbr, 63507 tbn, 59.94 tbc (defaul
t)
Metadata:
handler_name : VideoHandler
Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, flt
p, 128 kb/s (default)
Metadata:
handler_name : SoundHandler
[Parsed_ass_0 @ 03b938c0] Added subtitle file: 'subtitle.ass' (5 styles, 24 even
ts)
[libx264 @ 03c5d5c0] using SAR=1/1
[libx264 @ 03c5d5c0] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.1 Cache64
[libx264 @ 03c5d5c0] profile High, level 3.0
[libx264 @ 03c5d5c0] 264 - core 146 r2538 121396c - H.264/MPEG-4 AVC codec - Cop
yleft 2003-2015 - http://www.videolan.org/x264.html - options: cabac=1 ref=3 deb
lock=1:0:0 analyse=0x3:0x113 me=hex subme=7 psy=1 psy_rd=1.00:0.00 mixed_ref=1 m
e_range=16 chroma_me=1 trellis=1 8x8dct=1 cqm=0 deadzone=21,11 fast_pskip=1 chro
ma_qp_offset=-2 threads=3 lookahead_threads=1 sliced_threads=0 nr=0 decimate=1 i
nterlaced=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 scenec
ut=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 'output.mp4':
Metadata:
major_brand : isom
minor_version : 512
compatible_brands: isomiso2avc1mp41
encoder : Lavf56.37.100
Stream #0:0(und): Video: h264 (libx264) ([33][0][0][0] / 0x0021), yuv420p, 6
40x360 [SAR 1:1 DAR 16:9], q=-1--1, 29.97 fps, 63507 tbn, 29.97 tbc (default)
Metadata:
handler_name : VideoHandler
encoder : Lavc56.41.100 libx264
Stream #0:1(und): Audio: aac (libvo_aacenc) ([64][0][0][0] / 0x0040), 44100
Hz, stereo, s16, 128 kb/s (default)
Metadata:
handler_name : SoundHandler
encoder : Lavc56.41.100 libvo_aacenc
Stream mapping:
Stream #0:0 -> #0:0 (h264 (native) -> h264 (libx264))
Stream #0:1 -> #0:1 (aac (native) -> aac (libvo_aacenc))
Press [q] to stop, [?] for help
frame= 53 fps=0.0 q=29.0 size= 55kB time=00:00:01.79 bitrate= 248.9kbits/
frame= 75 fps= 73 q=29.0 size= 158kB time=00:00:02.54 bitrate= 508.7kbits/
frame= 95 fps= 61 q=29.0 size= 256kB time=00:00:03.19 bitrate= 657.4kbits/
frame= 115 fps= 54 q=29.0 size= 368kB time=00:00:03.86 bitrate= 779.2kbits/
frame= 132 fps= 50 q=29.0 size= 467kB time=00:00:04.44 bitrate= 861.0kbits/
frame= 149 fps= 48 q=29.0 size= 576kB time=00:00:05.00 bitrate= 943.9kbits/
frame= 166 fps= 46 q=29.0 size= 680kB time=00:00:05.55 bitrate=1002.4kbits/
frame= 182 fps= 44 q=29.0 size= 796kB time=00:00:06.09 bitrate=1069.8kbits/
frame= 197 fps= 42 q=29.0 size= 925kB time=00:00:06.60 bitrate=1147.3kbits/
frame= 213 fps= 41 q=29.0 size= 1033kB time=00:00:07.13 bitrate=1185.6kbits/
frame= 230 fps= 40 q=29.0 size= 1157kB time=00:00:07.69 bitrate=1231.3kbits/
frame= 245 fps= 39 q=29.0 size= 1261kB time=00:00:08.20 bitrate=1259.1kbits/
frame= 260 fps= 38 q=29.0 size= 1364kB time=00:00:08.71 bitrate=1281.5kbits/
frame= 275 fps= 37 q=29.0 size= 1479kB time=00:00:09.20 bitrate=1316.3kbits/
frame= 289 fps= 37 q=29.0 size= 1597kB time=00:00:09.66 bitrate=1352.9kbits/
frame= 305 fps= 36 q=29.0 size= 1731kB time=00:00:10.20 bitrate=1389.7kbits/
frame= 322 fps= 36 q=29.0 size= 1829kB time=00:00:10.78 bitrate=1389.0kbits/
frame= 338 fps= 36 q=29.0 size= 1945kB time=00:00:11.31 bitrate=1407.9kbits/
frame= 354 fps= 35 q=29.0 size= 2084kB time=00:00:11.85 bitrate=1440.6kbits/
frame= 370 fps= 35 q=29.0 size= 2214kB time=00:00:12.38 bitrate=1464.1kbits/
frame= 388 fps= 35 q=29.0 size= 2336kB time=00:00:12.96 bitrate=1475.9kbits/
frame= 404 fps= 35 q=29.0 size= 2443kB time=00:00:13.50 bitrate=1482.2kbits/
frame= 422 fps= 35 q=29.0 size= 2584kB time=00:00:14.10 bitrate=1500.7kbits/
frame= 439 fps= 35 q=29.0 size= 2702kB time=00:00:14.68 bitrate=1507.3kbits/
frame= 455 fps= 35 q=29.0 size= 2818kB time=00:00:15.21 bitrate=1516.8kbits/
frame= 471 fps= 34 q=29.0 size= 2930kB time=00:00:15.75 bitrate=1523.4kbits/
frame= 489 fps= 34 q=29.0 size= 3047kB time=00:00:16.35 bitrate=1525.9kbits/
frame= 507 fps= 34 q=29.0 size= 3153kB time=00:00:16.93 bitrate=1525.1kbits/
frame= 525 fps= 34 q=29.0 size= 3246kB time=00:00:17.54 bitrate=1516.1kbits/
frame= 544 fps= 34 q=29.0 size= 3353kB time=00:00:18.19 bitrate=1509.7kbits/
frame= 563 fps= 35 q=29.0 size= 3478kB time=00:00:18.81 bitrate=1514.2kbits/
frame= 583 fps= 34 q=29.0 size= 3590kB time=00:00:19.49 bitrate=1508.6kbits/
frame= 600 fps= 34 q=29.0 size= 3710kB time=00:00:20.04 bitrate=1515.9kbits/
frame= 614 fps= 34 q=29.0 size= 3818kB time=00:00:20.51 bitrate=1524.8kbits/
frame= 629 fps= 34 q=29.0 size= 3949kB time=00:00:21.02 bitrate=1538.9kbits/
frame= 645 fps= 34 q=29.0 size= 4075kB time=00:00:21.55 bitrate=1548.5kbits/
frame= 661 fps= 34 q=29.0 size= 4193kB time=00:00:22.09 bitrate=1554.9kbits/
frame= 680 fps= 34 q=29.0 size= 4315kB time=00:00:22.71 bitrate=1555.9kbits/
frame= 700 fps= 34 q=29.0 size= 4423kB time=00:00:23.39 bitrate=1548.9kbits/
frame= 719 fps= 34 q=29.0 size= 4527kB time=00:00:24.01 bitrate=1543.8kbits/
frame= 738 fps= 34 q=29.0 size= 4632kB time=00:00:24.64 bitrate=1539.5kbits/
frame= 758 fps= 34 q=29.0 size= 4747kB time=00:00:25.31 bitrate=1535.7kbits/
frame= 774 fps= 34 q=29.0 size= 4857kB time=00:00:25.85 bitrate=1539.0kbits/
frame= 790 fps= 34 q=29.0 size= 4967kB time=00:00:26.38 bitrate=1541.9kbits/
frame= 807 fps= 34 q=29.0 size= 5108kB time=00:00:26.96 bitrate=1551.6kbits/
frame= 825 fps= 34 q=29.0 size= 5223kB time=00:00:27.54 bitrate=1553.1kbits/
frame= 842 fps= 34 q=29.0 size= 5344kB time=00:00:28.12 bitrate=1556.4kbits/
frame= 861 fps= 34 q=29.0 size= 5489kB time=00:00:28.75 bitrate=1563.7kbits/
frame= 879 fps= 34 q=29.0 size= 5596kB time=00:00:29.36 bitrate=1561.3kbits/
frame= 897 fps= 34 q=29.0 size= 5705kB time=00:00:29.96 bitrate=1559.7kbits/
frame= 914 fps= 34 q=29.0 size= 5810kB time=00:00:30.52 bitrate=1559.6kbits/
frame= 929 fps= 34 q=29.0 size= 5914kB time=00:00:31.03 bitrate=1561.1kbits/
frame= 946 fps= 34 q=29.0 size= 6033kB time=00:00:31.58 bitrate=1564.6kbits/
frame= 961 fps= 34 q=29.0 size= 6154kB time=00:00:32.10 bitrate=1570.6kbits/
frame= 976 fps= 34 q=29.0 size= 6281kB time=00:00:32.58 bitrate=1578.8kbits/
frame= 991 fps= 33 q=29.0 size= 6396kB time=00:00:33.09 bitrate=1582.9kbits/
frame= 1007 fps= 33 q=29.0 size= 6496kB time=00:00:33.63 bitrate=1582.2kbits/
frame= 1021 fps= 33 q=29.0 size= 6575kB time=00:00:34.09 bitrate=1579.6kbits/
frame= 1038 fps= 33 q=29.0 size= 6662kB time=00:00:34.67 bitrate=1573.8kbits/
frame= 1054 fps= 33 q=29.0 size= 6767kB time=00:00:35.21 bitrate=1574.3kbits/
frame= 1069 fps= 33 q=29.0 size= 6834kB time=00:00:35.69 bitrate=1568.1kbits/
frame= 1086 fps= 33 q=29.0 size= 6932kB time=00:00:36.25 bitrate=1566.2kbits/
frame= 1103 fps= 33 q=29.0 size= 7015kB time=00:00:36.83 bitrate=1560.1kbits/
frame= 1121 fps= 33 q=29.0 size= 7104kB time=00:00:37.44 bitrate=1554.3kbits/
frame= 1137 fps= 33 q=29.0 size= 7176kB time=00:00:37.97 bitrate=1548.1kbits/
frame= 1157 fps= 33 q=29.0 size= 7255kB time=00:00:38.64 bitrate=1537.7kbits/
frame= 1171 fps= 33 q=29.0 size= 7315kB time=00:00:39.11 bitrate=1532.1kbits/
frame= 1184 fps= 33 q=29.0 size= 7377kB time=00:00:39.53 bitrate=1528.7kbits/
frame= 1204 fps= 33 q=29.0 size= 7478kB time=00:00:40.20 bitrate=1523.7kbits/
frame= 1224 fps= 33 q=29.0 size= 7566kB time=00:00:40.87 bitrate=1516.3kbits/
frame= 1238 fps= 33 q=29.0 size= 7651kB time=00:00:41.34 bitrate=1516.1kbits/
frame= 1253 fps= 33 q=29.0 size= 7763kB time=00:00:41.82 bitrate=1520.4kbits/
frame= 1270 fps= 33 q=29.0 size= 7890kB time=00:00:42.40 bitrate=1524.0kbits/
frame= 1286 fps= 33 q=29.0 size= 8012kB time=00:00:42.94 bitrate=1528.3kbits/
frame= 1300 fps= 33 q=29.0 size= 8147kB time=00:00:43.40 bitrate=1537.5kbits/
frame= 1317 fps= 33 q=29.0 size= 8267kB time=00:00:43.96 bitrate=1540.5kbits/
frame= 1332 fps= 33 q=29.0 size= 8365kB time=00:00:44.47 bitrate=1540.8kbits/
frame= 1347 fps= 33 q=29.0 size= 8470kB time=00:00:44.98 bitrate=1542.4kbits/
frame= 1365 fps= 33 q=29.0 size= 8573kB time=00:00:45.56 bitrate=1541.2kbits/
frame= 1383 fps= 33 q=29.0 size= 8706kB time=00:00:46.17 bitrate=1544.6kbits/
frame= 1398 fps= 33 q=29.0 size= 8797kB time=00:00:46.68 bitrate=1543.7kbits/
frame= 1414 fps= 33 q=29.0 size= 8905kB time=00:00:47.21 bitrate=1544.9kbits/
frame= 1432 fps= 33 q=29.0 size= 9008kB time=00:00:47.81 bitrate=1543.2kbits/
frame= 1451 fps= 33 q=29.0 size= 9125kB time=00:00:48.44 bitrate=1543.0kbits/
frame= 1467 fps= 33 q=29.0 size= 9233kB time=00:00:48.98 bitrate=1544.2kbits/
frame= 1483 fps= 33 q=29.0 size= 9340kB time=00:00:49.51 bitrate=1545.3kbits/
frame= 1500 fps= 33 q=29.0 size= 9461kB time=00:00:50.07 bitrate=1547.9kbits/
frame= 1515 fps= 33 q=29.0 size= 9566kB time=00:00:50.58 bitrate=1549.2kbits/
frame= 1532 fps= 33 q=29.0 size= 9685kB time=00:00:51.14 bitrate=1551.4kbits/
frame= 1542 fps= 33 q=29.0 size= 9758kB time=00:00:51.48 bitrate=1552.6kbits/
frame= 1559 fps= 33 q=29.0 size= 9908kB time=00:00:52.04 bitrate=1559.5kbits/
frame= 1577 fps= 33 q=29.0 size= 10035kB time=00:00:52.62 bitrate=1562.1kbits/
frame= 1593 fps= 33 q=29.0 size= 10145kB time=00:00:53.18 bitrate=1562.6kbits/
frame= 1609 fps= 33 q=29.0 size= 10247kB time=00:00:53.71 bitrate=1562.6kbits/
frame= 1627 fps= 33 q=29.0 size= 10360kB time=00:00:54.32 bitrate=1562.4kbits/
frame= 1645 fps= 33 q=29.0 size= 10462kB time=00:00:54.92 bitrate=1560.3kbits/
frame= 1664 fps= 33 q=29.0 size= 10552kB time=00:00:55.55 bitrate=1556.1kbits/
frame= 1681 fps= 33 q=29.0 size= 10637kB time=00:00:56.10 bitrate=1552.9kbits/
frame= 1699 fps= 33 q=29.0 size= 10729kB time=00:00:56.71 bitrate=1549.7kbits/
frame= 1716 fps= 33 q=29.0 size= 10800kB time=00:00:57.29 bitrate=1544.2kbits/
frame= 1733 fps= 33 q=29.0 size= 10880kB time=00:00:57.85 bitrate=1540.7kbits/
frame= 1752 fps= 33 q=29.0 size= 10948kB time=00:00:58.50 bitrate=1533.1kbits/
frame= 1770 fps= 33 q=29.0 size= 11025kB time=00:00:59.08 bitrate=1528.7kbits/
frame= 1790 fps= 33 q=29.0 size= 11098kB time=00:00:59.75 bitrate=1521.5kbits/
frame= 1810 fps= 33 q=29.0 size= 11203kB time=00:01:00.42 bitrate=1518.7kbits/
frame= 1828 fps= 33 q=29.0 size= 11280kB time=00:01:01.03 bitrate=1514.1kbits/
frame= 1847 fps= 33 q=29.0 size= 11367kB time=00:01:01.65 bitrate=1510.2kbits/
frame= 1866 fps= 33 q=29.0 size= 11457kB time=00:01:02.28 bitrate=1506.9kbits/
frame= 1883 fps= 33 q=29.0 size= 11546kB time=00:01:02.86 bitrate=1504.6kbits/
frame= 1899 fps= 33 q=29.0 size= 11647kB time=00:01:03.40 bitrate=1504.9kbits/
frame= 1916 fps= 33 q=29.0 size= 11751kB time=00:01:03.95 bitrate=1505.2kbits/
frame= 1930 fps= 33 q=29.0 size= 11849kB time=00:01:04.42 bitrate=1506.8kbits/
frame= 1943 fps= 33 q=29.0 size= 11949kB time=00:01:04.86 bitrate=1509.2kbits/
frame= 1957 fps= 33 q=29.0 size= 12057kB time=00:01:05.32 bitrate=1512.0kbits/
frame= 1973 fps= 33 q=29.0 size= 12196kB time=00:01:05.86 bitrate=1516.9kbits/
frame= 1987 fps= 33 q=29.0 size= 12305kB time=00:01:06.32 bitrate=1519.8kbits/
frame= 2003 fps= 33 q=29.0 size= 12423kB time=00:01:06.86 bitrate=1522.1kbits/
frame= 2018 fps= 33 q=29.0 size= 12533kB time=00:01:07.37 bitrate=1523.9kbits/
frame= 2034 fps= 33 q=29.0 size= 12651kB time=00:01:07.90 bitrate=1526.2kbits/
frame= 2051 fps= 33 q=29.0 size= 12789kB time=00:01:08.46 bitrate=1530.3kbits/
frame= 2066 fps= 33 q=29.0 size= 12891kB time=00:01:08.97 bitrate=1531.1kbits/
frame= 2083 fps= 33 q=29.0 size= 13017kB time=00:01:09.53 bitrate=1533.6kbits/
frame= 2100 fps= 33 q=29.0 size= 13125kB time=00:01:10.11 bitrate=1533.5kbits/
frame= 2118 fps= 33 q=29.0 size= 13240kB time=00:01:10.69 bitrate=1534.2kbits/
frame= 2137 fps= 33 q=29.0 size= 13351kB time=00:01:11.34 bitrate=1533.1kbits/
frame= 2157 fps= 33 q=29.0 size= 13468kB time=00:01:11.99 bitrate=1532.5kbits/
frame= 2176 fps= 33 q=29.0 size= 13565kB time=00:01:12.64 bitrate=1529.8kbits/
frame= 2193 fps= 33 q=29.0 size= 13672kB time=00:01:13.19 bitrate=1530.1kbits/
frame= 2208 fps= 33 q=29.0 size= 13767kB time=00:01:13.71 bitrate=1530.0kbits/
frame= 2228 fps= 33 q=29.0 size= 13872kB time=00:01:14.38 bitrate=1527.8kbits/
frame= 2246 fps= 33 q=29.0 size= 13976kB time=00:01:14.96 bitrate=1527.3kbits/
frame= 2263 fps= 33 q=29.0 size= 14081kB time=00:01:15.54 bitrate=1527.0kbits/
frame= 2281 fps= 33 q=29.0 size= 14183kB time=00:01:16.12 bitrate=1526.3kbits/
frame= 2296 fps= 33 q=26.0 size= 14265kB time=00:01:16.63 bitrate=1524.8kbits/
frame= 2313 fps= 33 q=29.0 size= 14400kB time=00:01:17.21 bitrate=1527.8kbits/
frame= 2324 fps= 32 q=-1.0 Lsize= 14851kB time=00:01:17.70 bitrate=1565.7kbits
/s
video:13553kB audio:1215kB subtitle:0kB other streams:0kB global headers:0kB mux
ing overhead: 0.565642%
[libx264 @ 03c5d5c0] frame I:10 Avg QP:23.07 size: 38966
[libx264 @ 03c5d5c0] frame P:1167 Avg QP:26.28 size: 9096
[libx264 @ 03c5d5c0] frame B:1147 Avg QP:31.55 size: 2504
[libx264 @ 03c5d5c0] consecutive B-frames: 2.5% 94.1% 3.1% 0.3%
[libx264 @ 03c5d5c0] mb I I16..4: 5.3% 22.2% 72.5%
[libx264 @ 03c5d5c0] mb P I16..4: 0.4% 1.3% 1.1% P16..4: 58.5% 16.1% 8.9%
0.0% 0.0% skip:13.6%
[libx264 @ 03c5d5c0] mb B I16..4: 0.1% 0.1% 0.1% B16..8: 54.8% 6.1% 1.8%
direct: 2.1% skip:34.9% L0:51.9% L1:37.5% BI:10.5%
[libx264 @ 03c5d5c0] 8x8 transform intra:41.3% inter:39.6%
[libx264 @ 03c5d5c0] coded y,uvDC,uvAC intra: 76.5% 70.7% 32.2% inter: 24.0% 17.
6% 2.4%
[libx264 @ 03c5d5c0] i16 v,h,dc,p: 31% 38% 8% 22%
[libx264 @ 03c5d5c0] i8 v,h,dc,ddl,ddr,vr,hd,vl,hu: 35% 16% 16% 4% 5% 7% 5%
7% 6%
[libx264 @ 03c5d5c0] i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 34% 22% 12% 4% 5% 6% 6%
6% 5%
[libx264 @ 03c5d5c0] i8c dc,h,v,p: 48% 22% 23% 7%
[libx264 @ 03c5d5c0] Weighted P-Frames: Y:0.0% UV:0.0%
[libx264 @ 03c5d5c0] ref P L0: 69.6% 21.7% 6.8% 1.9%
[libx264 @ 03c5d5c0] ref B L0: 91.8% 8.2% 0.0%
[libx264 @ 03c5d5c0] ref B L1: 99.6% 0.4%
[libx264 @ 03c5d5c0] kb/s:1431.69
我检查了这里并且没有其他选择。
答案1
出现模糊的原因是您正在重新编码整个视频，而不是因为字幕刻录机有故障。
我建议指定 H.264 作为您的视频编解码器并同时复制音轨，否则 ffmpeg 将使用 libvo_aacenc 对其进行重新编码：
ffmpeg -i input.mp4 -vf "ass=subtitle.ass" -vcodec libx264 -x264-params crf=18 -preset veryslow -acodec copy out.mp4
如果输出太大，请随意将 crf 值更改为更高的值（原始命令中使用的 x264 默认 crf 是 23），如果编码太慢，则将预设为更快的值。
编辑：我忘记了最重要的部分。您的视频是 640x360，因此字幕在此分辨率下会烧毁。虽然如果在此分辨率下播放视频，字幕会很清晰，但一旦视频升级到显示器的输出，字幕就会变得模糊。如果您的显示器是 1080p，字幕出现模糊是完全正常的。
你最后的希望就是升级视频，这里有一个 720p 的示例：
ffmpeg -i input.mp4 -s 1280x720 -sws_flags lanczos -vf "ass=subtitle.ass" -vcodec libx264 -x264-params crf=18 -preset veryslow -acodec copy out.mp4
但是，这将生成一个更大的文件，并且不会提高质量，除非是在订阅上。