我目前正在我的 Android 应用程序上使用 ffmpeg 的实现。我允许用户在我的应用程序中拍摄短视频，然后当他们将它们上传到服务器时，我会使用 ffmpeg 对其进行处理以减小文件大小，这样他们就不会通过网络传递大量数据。
问题是，在 Android 设备上对视频进行编码需要很长时间。这些视频通常不超过 45 秒，编码可能需要 20 分钟。我已经在 ffmpeg 命令行上尝试了一些不同的开关/参数，现在我可以在更舒适的时间使用它，但文件大小明显更大。我只是不确定我应该使用什么编解码器（最快的编码但具有良好的质量输出），ffmpeg 如何处理编码速度等方面的大小变化（长宽比）。
这是我一直在使用的两个命令。第一个输出我想要的文件大小/质量，但编码时间太长，更不用说它使我的设备在编码这么长时间时变得非常热：
ffmpeg -i input.mp4 -b:v 1024k -c:a copy -vf scale=960:540 output.mp4
我已经调整了一些比特率，并将比例更改为较小的尺寸，但我不想让视频非常小（就比例而言）来完成更快的编码。第二个命令运行速度更快，但文件大小明显变大：
ffmpeg -i input.mp4 -vcodec libx264 -preset fast -c:a copy -s 960x540 output.mp4
我想找到一种令人满意的媒介（文件大小较小但编码速度更快），使视频缩放大小接近原始大小。 ffmpeg 有太多不同的参数/开关，以至于很难让我明白我应该做什么。
编辑：添加 ffmpeg 输出。
ffmpeg -i input.mp4 -vcodec libx264 -crf 30 -preset veryfast -c:a copy -s 960x540 output.mp4
09-13 11:06:28.330 10881-10881/someapp D/home: ffmpeg version n3.0.1 Copyright (c) 2000-2016 the FFmpeg developers
09-13 11:06:28.330 10881-10881/someapp D/home: built with gcc 4.8 (GCC)
09-13 11:06:28.331 10881-10881/someapp D/home: configuration: --target-os=linux --cross-prefix=/home/vagrant/SourceCode/ffmpeg-android/toolchain-android/bin/arm-linux-androideabi- --arch=arm --cpu=cortex-a8 --enable-runtime-cpudetect --sysroot=/home/vagrant/SourceCode/ffmpeg-android/toolchain-android/sysroot --enable-pic --enable-libx264 --enable-libass --enable-libfreetype --enable-libfribidi --enable-libmp3lame --enable-fontconfig --enable-pthreads --disable-debug --disable-ffserver --enable-version3 --enable-hardcoded-tables --disable-ffplay --disable-ffprobe --enable-gpl --enable-yasm --disable-doc --disable-shared --enable-static --pkg-config=/home/vagrant/SourceCode/ffmpeg-android/ffmpeg-pkg-config --prefix=/home/vagrant/SourceCode/ffmpeg-android/build/armeabi-v7a --extra-cflags='-I/home/vagrant/SourceCode/ffmpeg-android/toolchain-android/include -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=2 -fno-strict-overflow -fstack-protector-all' --extra-ldflags='-L/home/vagrant/SourceCode/ffmpeg-android/toolchain-android/lib -Wl,-z,relro -Wl,-z,now -pie' --extra-libs='-lpng -lexpat -lm' --extra-cxxflags=
09-13 11:06:28.331 10881-10881/someapp D/home: libavutil 55. 17.103 / 55. 17.103
09-13 11:06:28.331 10881-10881/someapp D/home: libavcodec 57. 24.102 / 57. 24.102
09-13 11:06:28.331 10881-10881/someapp D/home: libavformat 57. 25.100 / 57. 25.100
09-13 11:06:28.331 10881-10881/someapp D/home: libavdevice 57. 0.101 / 57. 0.101
09-13 11:06:28.331 10881-10881/someapp D/home: libavfilter 6. 31.100 / 6. 31.100
09-13 11:06:28.331 10881-10881/someapp D/home: libswscale 4. 0.100 / 4. 0.100
09-13 11:06:28.331 10881-10881/someapp D/home: libswresample 2. 0.101 / 2. 0.101
09-13 11:06:28.331 10881-10881/someapp D/home: libpostproc 54. 0.100 / 54. 0.100
09-13 11:06:28.430 10881-10881/someapp D/home: Input #0, mov,mp4,m4a,3gp,3g2,mj2, from '/storage/emulated/0/ExpeditionSpot/Videos/20160913110411.mp4':
09-13 11:06:28.430 10881-10881/someapp D/home: Metadata:
09-13 11:06:28.430 10881-10881/someapp D/home: major_brand : mp42
09-13 11:06:28.430 10881-10881/someapp D/home: minor_version : 0
09-13 11:06:28.430 10881-10881/someapp D/home: compatible_brands: isommp42
09-13 11:06:28.430 10881-10881/someapp D/home: creation_time : 2016-09-13 17:04:33
09-13 11:06:28.430 10881-10881/someapp D/home: com.android.version: 6.0.1
09-13 11:06:28.430 10881-10881/someapp D/home: Duration: 00:00:19.41, start: 0.000000, bitrate: 20222 kb/s
09-13 11:06:28.430 10881-10881/someapp D/home: Stream #0:0(eng): Video: h264 (Baseline) (avc1 / 0x31637661), yuv420p, 1920x1080, 19963 kb/s, SAR 1:1 DAR 16:9, 30.03 fps, 30 tbr, 90k tbn, 180k tbc (default)
09-13 11:06:28.430 10881-10881/someapp D/home: Metadata:
09-13 11:06:28.430 10881-10881/someapp D/home: creation_time : 2016-09-13 17:04:33
09-13 11:06:28.430 10881-10881/someapp D/home: handler_name : VideoHandle
09-13 11:06:28.431 10881-10881/someapp D/home: Stream #0:1(eng): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 96 kb/s (default)
09-13 11:06:28.431 10881-10881/someapp D/home: Metadata:
09-13 11:06:28.431 10881-10881/someapp D/home: creation_time : 2016-09-13 17:04:33
09-13 11:06:28.431 10881-10881/someapp D/home: handler_name : SoundHandle
09-13 11:06:28.448 10881-10881/someapp D/home: [libx264 @ 0xf71c4400] using SAR=1/1
09-13 11:06:28.448 10881-10881/someapp D/home: [libx264 @ 0xf71c4400] using cpu capabilities: none!
09-13 11:06:28.516 10881-10881/someapp D/home: [libx264 @ 0xf71c4400] profile High, level 3.1
09-13 11:06:28.516 10881-10881/someapp D/home: [libx264 @ 0xf71c4400] 264 - core 148 - H.264/MPEG-4 AVC codec - Copyleft 2003-2015 - http://www.videolan.org/x264.html - options: cabac=1 ref=1 deblock=1:0:0 analyse=0x3:0x113 me=hex subme=2 psy=1 psy_rd=1.00:0.00 mixed_ref=0 me_range=16 chroma_me=1 trellis=0 8x8dct=1 cqm=0 deadzone=21,11 fast_pskip=1 chroma_qp_offset=0 threads=12 lookahead_threads=4 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=1 keyint=250 keyint_min=25 scenecut=40 intra_refresh=0 rc_lookahead=10 rc=crf mbtree=1 crf=27.0 qcomp=0.60 qpmin=0 qpmax=69 qpstep=4 ip_ratio=1.40 aq=1:1.00
09-13 11:06:28.532 10881-10881/someapp D/home: Output #0, mp4, to '/storage/emulated/0/ExpeditionSpot/.tmp/small-20160913110411.mp4':
09-13 11:06:28.532 10881-10881/someapp D/home: Metadata:
09-13 11:06:28.532 10881-10881/someapp D/home: major_brand : mp42
09-13 11:06:28.533 10881-10881/someapp D/home: minor_version : 0
09-13 11:06:28.533 10881-10881/someapp D/home: compatible_brands: isommp42
09-13 11:06:28.533 10881-10881/someapp D/home: com.android.version: 6.0.1
09-13 11:06:28.533 10881-10881/someapp D/home: encoder : Lavf57.25.100
09-13 11:06:28.533 10881-10881/someapp D/home: Stream #0:0(eng): Video: h264 (libx264) ([33][0][0][0] / 0x0021), yuv420p, 960x540 [SAR 1:1 DAR 16:9], q=-1--1, 30 fps, 15360 tbn, 30 tbc (default)
09-13 11:06:28.533 10881-10881/someapp D/home: Metadata:
09-13 11:06:28.533 10881-10881/someapp D/home: creation_time : 2016-09-13 17:04:33
09-13 11:06:28.533 10881-10881/someapp D/home: handler_name : VideoHandle
09-13 11:06:28.533 10881-10881/someapp D/home: encoder : Lavc57.24.102 libx264
09-13 11:06:28.533 10881-10881/someapp D/home: Side data:
09-13 11:06:28.533 10881-10881/someapp D/home: unknown side data type 10 (24 bytes)
09-13 11:06:28.533 10881-10881/someapp D/home: Stream #0:1(eng): Audio: aac (LC) ([64][0][0][0] / 0x0040), 48000 Hz, stereo, 96 kb/s (default)
09-13 11:06:28.533 10881-10881/someapp D/home: Metadata:
09-13 11:06:28.533 10881-10881/someapp D/home: creation_time : 2016-09-13 17:04:33
09-13 11:06:28.533 10881-10881/someapp D/home: handler_name : SoundHandle
09-13 11:06:28.533 10881-10881/someapp D/home: Stream mapping:
09-13 11:06:28.533 10881-10881/someapp D/home: Stream #0:0 -> #0:0 (h264 (native) -> h264 (libx264))
09-13 11:06:28.533 10881-10881/someapp D/home: Stream #0:1 -> #0:1 (copy)
09-13 11:06:28.533 10881-10881/someapp D/home: Press [q] to stop, [?] for help
09-13 11:06:29.102 10881-10881/someapp D/home: frame= 7 fps=0.0 q=0.0 size= 0kB time=00:00:01.04 bitrate= 0.4kbits/s speed=2.08x
09-13 11:06:29.699 10881-10881/someapp D/home: frame= 16 fps= 15 q=0.0 size= 0kB time=00:00:01.04 bitrate= 0.4kbits/s speed=0.998x
....
09-13 11:07:12.674 10881-10881/someapp D/home: [libx264 @ 0xf71c4400] frame I:3 Avg QP:26.83 size: 21896
09-13 11:07:12.674 10881-10881/someapp D/home: [libx264 @ 0xf71c4400] frame P:279 Avg QP:28.76 size: 5859
09-13 11:07:12.674 10881-10881/someapp D/home: [libx264 @ 0xf71c4400] frame B:296 Avg QP:29.93 size: 863
09-13 11:07:12.674 10881-10881/someapp D/home: [libx264 @ 0xf71c4400] consecutive B-frames: 18.3% 32.2% 23.9% 25.6%
09-13 11:07:12.674 10881-10881/someapp D/home: [libx264 @ 0xf71c4400] mb I I16..4: 16.9% 54.2% 28.9%
09-13 11:07:12.674 10881-10881/someapp D/home: [libx264 @ 0xf71c4400] mb P I16..4: 7.7% 9.1% 0.4% P16..4: 27.5% 11.1% 4.0% 0.0% 0.0% skip:40.1%
09-13 11:07:12.674 10881-10881/someapp D/home: [libx264 @ 0xf71c4400] mb B I16..4: 0.8% 0.6% 0.0% B16..8: 10.9% 2.4% 0.1% direct: 1.8% skip:83.5% L0:35.8% L1:54.2% BI:10.0%
09-13 11:07:12.675 10881-10881/someapp D/home: [libx264 @ 0xf71c4400] 8x8 transform intra:52.0% inter:41.3%
09-13 11:07:12.675 10881-10881/someapp D/home: [libx264 @ 0xf71c4400] coded y,uvDC,uvAC intra: 28.9% 26.0% 2.1% inter: 6.4% 5.0% 0.0%
09-13 11:07:12.675 10881-10881/someapp D/home: [libx264 @ 0xf71c4400] i16 v,h,dc,p: 57% 20% 17% 6%
09-13 11:07:12.675 10881-10881/someapp D/home: [libx264 @ 0xf71c4400] i8 v,h,dc,ddl,ddr,vr,hd,vl,hu: 33% 23% 34% 1% 2% 1% 3% 2% 2%
09-13 11:07:12.675 10881-10881/someapp D/home: [libx264 @ 0xf71c4400] i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 36% 21% 17% 2% 7% 4% 6% 4% 4%
09-13 11:07:12.675 10881-10881/someapp D/home: [libx264 @ 0xf71c4400] i8c dc,h,v,p: 59% 16% 23% 2%
09-13 11:07:12.675 10881-10881/someapp D/home: [libx264 @ 0xf71c4400] Weighted P-Frames: Y:16.8% UV:4.7%
09-13 11:07:12.675 10881-10881/someapp D/home: [libx264 @ 0xf71c4400] kb/s:812.09
尝试
ffmpeg -i input.mp4 -vcodec libx264 -crf 27 -preset veryfast -c:a copy -s 960x540 output.mp4
在CRF模式下，x264对视频进行编码以保持一定的质量。较低的值会产生较高质量但较大的文件。与
veryfastffmpeg，x264 1 pass 转换，具有良好的压缩和质量以及合理的文件大小，例如：
视频：
-c:v libx264 -preset veryfast -tune film -crf 22 -s 640x360 -aspect 16:9 -g 250 -r 25
音频：
-c:a aac -b:a 128k -ac 2 -ar 44100
Asamof：crf 20 到 23。如果您想保留原始内容，可以省略 fps (-r 25)。除了 crf 和大小之外，最能减少文件大小的因素之一是 gop 大小 (-g)，也称为关键帧间隔。不过，如果您打算更精确地剪切视频，我建议将 gop 设置为（0 到）12（对于 25 fps 的电影，为 fps 的一半）。如果您不打算剪切/编辑太多，只想按原样转换，我会说默认 gop 为 250。
音频对大小的影响较小。 96（合理）和 128 kbps（CD 质量，首选）之间。
当然，您也可以在 Avidemux 中进行这些转换（和编辑）（http://fixounet.free.fr/avidemux/）。在其中的“视频输出，配置”中，您可以使用或不使用高级模式（并进行自己的设置）。 gop 位于“框架”选项卡下。
再见。
P.S.：请勿在 Android 设备上对视频进行转码。使用一台像样的笔记本电脑，最好有 2 个或更多内核和 4 个或更多 G(i)b 内存。电脑的其他优点：你可以用 1 到 10 个手指打字！ ;-P