我希望水印缩放到与输出文件相同的分辨率。我该怎么做呢？ 或者，我怎样才能将水印置于输出的中间？
以下是我所拥有的：
ffmpeg -i input.mp4 -i watermark.png -filter_complex \
"[0:v]scale=min(640\, iw):-1[scaled]; \
[scaled][1:v]overlay[scaledwatermarked]; \
[scaledwatermarked]drawtext=fontfile=/path/to/FreeSans.ttf:text='TEST':\
x=0:y=0[text]" -map "[text]" \
-vcodec libx264 output.mov
因此，我使用 缩放输入电影文件scale=min(640\, iw):-1，即水平方向最大缩放至 640 像素，同时保持输入电影文件的纵横比。然后我添加水印和一些文本。
水印应缩放至与输出文件相同的大小，忽略水印文件的最终纵横比。它应被拉伸或收缩以适合输出的宽度和高度，忽略水印文件的原始纵横比。使用上述命令，水印文件将被截断而不是缩放。
（为了清楚起见，我从命令中删除了一些质量、时间码和音频选项。）
以下是 ffmpeg 的输出：
ffmpeg version 2.1.1 Copyright (c) 2000-2013 the FFmpeg developers
built on Dec 7 2013 16:02:05 with gcc 4.2.1 (GCC) (Apple Inc. build 5577)
configuration: --prefix=/opt/local --enable-swscale --enable-avfilter --enable-avresample --enable-libmp3lame --enable-libvorbis --enable-libopus --enable-libtheora --enable-libschroedinger --enable-libopenjpeg --enable-libmodplug --enable-libvpx --enable-libspeex --enable-libass --enable-libbluray --enable-gnutls --enable-libfreetype --disable-indev=jack --disable-outdev=xv --mandir=/opt/local/share/man --enable-shared --enable-pthreads --cc=/usr/bin/gcc-4.2 --arch=i386 --enable-yasm --enable-gpl --enable-postproc --enable-libx264 --enable-libxvid --enable-nonfree --enable-libfaac
libavutil 52. 48.101 / 52. 48.101
libavcodec 55. 39.101 / 55. 39.101
libavformat 55. 19.104 / 55. 19.104
libavdevice 55. 5.100 / 55. 5.100
libavfilter 3. 90.100 / 3. 90.100
libavresample 1. 1. 0 / 1. 1. 0
libswscale 2. 5.101 / 2. 5.101
libswresample 0. 17.104 / 0. 17.104
libpostproc 52. 3.100 / 52. 3.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'input.mp4':
Metadata:
major_brand : mp42
minor_version : 1
compatible_brands: mp42mp41
creation_time : 2013-12-04 18:19:48
Duration: 01:00:04.67, start: 0.000000, bitrate: 4182 kb/s
Stream #0:0(eng): Video: mpeg4 (Advanced Simple Profile) (mp4v / 0x7634706D), yuv420p, 1280x720 [SAR 1:1 DAR 16:9], 3923 kb/s, 23.98 fps, 23.98 tbr, 2398 tbn, 1k tbc (default)
Metadata:
creation_time : 2013-12-04 18:19:48
handler_name : Apple Video Media Handler
Stream #0:1(eng): Audio: aac (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 255 kb/s (default)
Metadata:
creation_time : 2013-12-04 18:19:48
handler_name : Apple Sound Media Handler
Input #1, image2, from 'watermark.png':
Duration: 00:00:00.04, start: 0.000000, bitrate: N/A
Stream #1:0: Video: png, rgba, 640x480 [SAR 2835:2835 DAR 4:3], 25 tbr, 25 tbn, 25 tbc
[libx264 @ 0x300f620] using SAR=1/1
[libx264 @ 0x300f620] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.1 Cache64
[libx264 @ 0x300f620] profile High, level 3.0
[libx264 @ 0x300f620] 264 - core 136 - H.264/MPEG-4 AVC codec - Copyleft 2003-2013 - http://www.videolan.org/x264.html - options: cabac=1 ref=5 deblock=1:0:0 analyse=0x3:0x113 me=umh subme=8 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=12 lookahead_threads=2 sliced_threads=0 nr=0 decimate=1 interlaced=0 bluray_compat=0 constrained_intra=0 bframes=3 b_pyramid=2 b_adapt=2 b_bias=0 direct=3 weightb=1 open_gop=0 weightp=2 keyint=250 keyint_min=23 scenecut=40 intra_refresh=0 rc_lookahead=50 rc=crf mbtree=1 crf=18.0 qcomp=0.60 qpmin=0 qpmax=69 qpstep=4 vbv_maxrate=5000 vbv_bufsize=5000 crf_max=0.0 nal_hrd=none ip_ratio=1.40 aq=1:1.00
Output #0, mp4, to 'output.mov':
Metadata:
major_brand : mp42
minor_version : 1
compatible_brands: mp42mp41
encoder : Lavf55.19.104
Stream #0:0: Video: h264 (libx264) ([33][0][0][0] / 0x0021), yuv420p, 640x360 [SAR 1:1 DAR 16:9], q=-1--1, max. 5000 kb/s, 19184 tbn, 23.98 tbc (default)
Stream mapping:
Stream #0:0 (mpeg4) -> scale
Stream #1:0 (png) -> overlay:overlay
drawtext -> Stream #0:0 (libx264)
Press [q] to stop, [?] for help
frame= 552 fps= 64 q=-1.0 Lsize= 5218kB time=00:00:22.93 bitrate=1863.8kbits/s
video:5211kB audio:0kB subtitle:0 global headers:0kB muxing overhead 0.140648%
[libx264 @ 0x300f620] frame I:5 Avg QP:17.84 size: 34541
[libx264 @ 0x300f620] frame P:144 Avg QP:19.27 size: 16691
[libx264 @ 0x300f620] frame B:403 Avg QP:21.00 size: 6846
[libx264 @ 0x300f620] consecutive B-frames: 1.3% 1.1% 9.2% 88.4%
[libx264 @ 0x300f620] mb I I16..4: 37.9% 33.1% 29.0%
[libx264 @ 0x300f620] mb P I16..4: 2.2% 6.8% 1.8% P16..4: 30.8% 34.1% 20.4% 0.0% 0.0% skip: 3.8%
[libx264 @ 0x300f620] mb B I16..4: 0.7% 0.7% 0.2% B16..8: 41.1% 19.1% 10.2% direct:12.8% skip:15.1% L0:46.2% L1:43.9% BI: 9.9%
[libx264 @ 0x300f620] 8x8 transform intra:52.6% inter:31.2%
[libx264 @ 0x300f620] direct mvs spatial:98.3% temporal:1.7%
[libx264 @ 0x300f620] coded y,uvDC,uvAC intra: 91.2% 85.9% 59.9% inter: 51.7% 33.6% 9.4%
[libx264 @ 0x300f620] i16 v,h,dc,p: 8% 34% 36% 22%
[libx264 @ 0x300f620] i8 v,h,dc,ddl,ddr,vr,hd,vl,hu: 6% 19% 10% 8% 11% 9% 13% 8% 16%
[libx264 @ 0x300f620] i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 11% 15% 8% 8% 11% 11% 12% 10% 16%
[libx264 @ 0x300f620] i8c dc,h,v,p: 49% 31% 13% 7%
[libx264 @ 0x300f620] Weighted P-Frames: Y:4.9% UV:4.9%
[libx264 @ 0x300f620] ref P L0: 46.8% 13.7% 22.3% 8.1% 8.4% 0.6% 0.1%
[libx264 @ 0x300f620] ref B L0: 89.8% 7.1% 2.0% 1.0%
[libx264 @ 0x300f620] ref B L1: 98.5% 1.5%
[libx264 @ 0x300f620] kb/s:1854.19
例子：
input.mp4 为 640x100。watermark.png 为 640x480。输出将为 640x100。如何告诉 ffmpeg 将 watermark.png 缩放到 640x100 而不是将其剪切到 640x100？
另外，我如何告诉 ffmpeg 将 watermark.png 放在中心，即在此示例中在输出文件中将其中心点放在 (320,50) 处？