我在 iPhone 上录制了两个视频。一个是纵向录制的，另一个是横向录制的：
肖像视频：
ffprobe version 4.2.2 Copyright (c) 2007-2019 the FFmpeg developers
built with Apple clang version 11.0.0 (clang-1100.0.33.17)
configuration: --prefix=/usr/local/Cellar/ffmpeg/4.2.2_2 --enable-shared --enable-pthreads --enable-version3 --enable-avresample --cc=clang --host-cflags= --host-ldflags= --enable-ffplay --enable-gnutls --enable-gpl --enable-libaom --enable-libbluray --enable-libmp3lame --enable-libopus --enable-librubberband --enable-libsnappy --enable-libtesseract --enable-libtheora --enable-libvidstab --enable-libvorbis --enable-libvpx --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxvid --enable-lzma --enable-libfontconfig --enable-libfreetype --enable-frei0r --enable-libass --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-librtmp --enable-libspeex --enable-libsoxr --enable-videotoolbox --disable-libjack --disable-indev=jack
libavutil 56. 31.100 / 56. 31.100
libavcodec 58. 54.100 / 58. 54.100
libavformat 58. 29.100 / 58. 29.100
libavdevice 58. 8.100 / 58. 8.100
libavfilter 7. 57.100 / 7. 57.100
libavresample 4. 0. 0 / 4. 0. 0
libswscale 5. 5.100 / 5. 5.100
libswresample 3. 5.100 / 3. 5.100
libpostproc 55. 5.100 / 55. 5.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'IMG_7386.MOV':
Metadata:
major_brand : qt
minor_version : 0
compatible_brands: qt
creation_time : 2020-04-21T02:00:00.000000Z
com.apple.quicktime.make: Apple
com.apple.quicktime.model: iPhone XS
com.apple.quicktime.software: 13.3.1
com.apple.quicktime.creationdate: 2020-04-20T22:00:00-0400
Duration: 00:00:41.00, start: 0.000000, bitrate: 9994 kb/s
Stream #0:0(und): Video: hevc (Main) (hvc1 / 0x31637668), yuv420p(tv, bt709), 1920x1080, 9782 kb/s, 29.41 fps, 29.97 tbr, 600 tbn, 600 tbc (default)
Metadata:
rotate : 90
creation_time : 2020-04-21T02:00:00.000000Z
handler_name : Core Media Video
encoder : HEVC
Side data:
displaymatrix: rotation of -90.00 degrees
Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 171 kb/s (default)
Metadata:
creation_time : 2020-04-21T02:00:00.000000Z
handler_name : Core Media Audio
Stream #0:2(und): Data: none (mebx / 0x7862656D), 6 kb/s (default)
Metadata:
creation_time : 2020-04-21T02:00:00.000000Z
handler_name : Core Media Metadata
Stream #0:3(und): Data: none (mebx / 0x7862656D), 0 kb/s (default)
Metadata:
creation_time : 2020-04-21T02:00:00.000000Z
handler_name : Core Media Metadata
Stream #0:4(und): Data: none (mebx / 0x7862656D), 18 kb/s (default)
Metadata:
creation_time : 2020-04-21T02:00:00.000000Z
handler_name : Core Media Metadata
Unsupported codec with id 0 for input stream 2
Unsupported codec with id 0 for input stream 3
Unsupported codec with id 0 for input stream 4
风景视频：
ffprobe version 4.2.2 Copyright (c) 2007-2019 the FFmpeg developers
built with Apple clang version 11.0.0 (clang-1100.0.33.17)
configuration: --prefix=/usr/local/Cellar/ffmpeg/4.2.2_2 --enable-shared --enable-pthreads --enable-version3 --enable-avresample --cc=clang --host-cflags= --host-ldflags= --enable-ffplay --enable-gnutls --enable-gpl --enable-libaom --enable-libbluray --enable-libmp3lame --enable-libopus --enable-librubberband --enable-libsnappy --enable-libtesseract --enable-libtheora --enable-libvidstab --enable-libvorbis --enable-libvpx --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxvid --enable-lzma --enable-libfontconfig --enable-libfreetype --enable-frei0r --enable-libass --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-librtmp --enable-libspeex --enable-libsoxr --enable-videotoolbox --disable-libjack --disable-indev=jack
libavutil 56. 31.100 / 56. 31.100
libavcodec 58. 54.100 / 58. 54.100
libavformat 58. 29.100 / 58. 29.100
libavdevice 58. 8.100 / 58. 8.100
libavfilter 7. 57.100 / 7. 57.100
libavresample 4. 0. 0 / 4. 0. 0
libswscale 5. 5.100 / 5. 5.100
libswresample 3. 5.100 / 3. 5.100
libpostproc 55. 5.100 / 55. 5.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'IMG_7168.MOV':
Metadata:
major_brand : qt
minor_version : 0
compatible_brands: qt
creation_time : 2020-04-13T21:00:14.000000Z
com.apple.quicktime.make: Apple
com.apple.quicktime.model: iPhone XS
com.apple.quicktime.software: 13.3.1
com.apple.quicktime.creationdate: 2020-04-13T17:00:13-0400
Duration: 00:00:00.57, start: 0.000000, bitrate: 10809 kb/s
Stream #0:0(und): Video: hevc (Main) (hvc1 / 0x31637668), yuv420p(tv, bt709), 1920x1080, 10477 kb/s, 30 fps, 30 tbr, 600 tbn, 600 tbc (default)
Metadata:
creation_time : 2020-04-13T21:00:14.000000Z
handler_name : Core Media Video
encoder : HEVC
Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 189 kb/s (default)
Metadata:
creation_time : 2020-04-13T21:00:14.000000Z
handler_name : Core Media Audio
Stream #0:2(und): Data: none (mebx / 0x7862656D), 0 kb/s (default)
Metadata:
creation_time : 2020-04-13T21:00:14.000000Z
handler_name : Core Media Metadata
Stream #0:3(und): Data: none (mebx / 0x7862656D), 0 kb/s (default)
Metadata:
creation_time : 2020-04-13T21:00:14.000000Z
handler_name : Core Media Metadata
Stream #0:4(und): Data: none (mebx / 0x7862656D), 17 kb/s (default)
Metadata:
creation_time : 2020-04-13T21:00:14.000000Z
handler_name : Core Media Metadata
Unsupported codec with id 0 for input stream 2
Unsupported codec with id 0 for input stream 3
Unsupported codec with id 0 for input stream 4
这些视频的区别在于，肖像视频displaymatrix: rotation of -90.00 degrees中有侧面数据Stream #0:0。
我想使用以下命令调整这些视频的大小：
ffmpeg -y -i $filename -filter:v scale=-1:720 -vcodec libx265 -crf 30 output.mp4
但是，scale=-1:720仅适用于横向视频。要缩放纵向视频，我需要将命令更改为scale=720:-1。否则我会收到错误：
[libx265 @ 0x7f9ae1009c00] Cannot open libx265 encoder.
Error initializing output stream 0:0 -- Error while opening encoder for output stream #0:0 - maybe incorrect parameters such as bit_rate, rate, width or height
有没有办法让比例过滤器适应任何方向？我希望长边缩放到 720，无论是宽度还是高度。
答案1
这里有两个问题。
1) 无法成功初始化 x265 编码器。2
) 由于潜在的旋转，您无法瞄准正确的一侧。
对于 1.，您需要设置-2而不是，-1因为编码器需要均匀尺寸的默认输出像素格式。
对于 2. 你需要规模中的条件表达式，scale=w='if(gt(iw\,ih),720,-2)':h='if(gt(iw\,ih),-2,720)'