问题
I'm currently using an implementation of ffmpeg on my android app. I'm allowing users to take short videos within my app and then when they upload them to the server, I'm crunching them down with ffmpeg to decrease file size so they're not passing huge amounts of data over the wire.
the problem is, it's taking forever to encode the videos on the android device. These videos usually aren't longer than 45 seconds and can take 20 minutes to encode. I've done some playing around with different switches / parameters on the ffmpeg command line and I now have it at a more comfortable time, but the file sizes are significantly bigger. I'm just not sure what codec I should use (fastest encoding but with decent quality output), how ffmpeg handles changing size (aspect ratio) in terms of speed of encoding etc.
Here are the two commands I've been using. This first one outputs the file size / quality that I want, but it just takes way too long to encode, not to mention it makes my device get really hot while it's encoding for so long:
ffmpeg -i input.mp4 -b:v 1024k -c:a copy -vf scale=960:540 output.mp4
I've tweaked the bitrate some on that as well as changed the scale to a smaller size, but I don't want to have to make the videos really small (in terms of scale) to accomplish a faster encoding. this second command goes a lot faster but makes the file size significantly bigger:
ffmpeg -i input.mp4 -vcodec libx264 -preset fast -c:a copy -s 960x540 output.mp4
I'd like to find a happy medium (smaller file size but faster encoding) keeping the video scale size close to the original. ffmpeg just has so many different parameters / switches that it's difficult to wrap my head around what I should be doing.
EDIT: adding ffmpeg output.
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
回答1:
Try
ffmpeg -i input.mp4 -vcodec libx264 -crf 27 -preset veryfast -c:a copy -s 960x540 output.mp4
In CRF mode, x264 encodes video to maintain a certain quality throughout. Lower values produce higher quality but larger files. Combined with veryfast preset, it should provide an acceptable tradeoff between speed and size.
来源：https://stackoverflow.com/questions/39473434/ffmpeg-command-for-faster-encoding-at-a-decent-bitrate-with-smaller-file-size