我有一堆高带宽 AVC 视频文件，我想将它们重新编码为较低的比特率，以使这种转换尽可能无损。
因此我想保留原始帧速率。有些文件的帧速率可变：
$ mediainfo "$SOURCE".mp4|grep -i frame
Format settings : CABAC / 1 Ref Frames
Format settings, Reference frames : 1 frame
Frame rate mode : Variable
Frame rate : 29.970 (29970/1000) FPS
Minimum frame rate : 25.395 FPS
Maximum frame rate : 30.090 FPS
Bits/(Pixel*Frame) : 0.322
Frame rate : 46.875 FPS (1024 SPF)
但重新编码后：
ffmpeg -i "$SOURCE".mp4 -vsync 0 -c:v libvpx-vp9 -crf 30 -b:v 0 -c:a copy "$OUT".mp4
生成的文件具有恒定的 CFR：
$ mediainfo "$OUT".mp4|grep -i frame
Frame rate mode : Constant
Frame rate : 30.000 FPS
Bits/(Pixel*Frame) : 0.132
Frame rate : 46.875 FPS (1024 SPF)
我认为-vsync 0应该可以解决问题。我遗漏了什么？
更新：每个请求的完整日志：
ffmpeg -i VID_20191130_125715.mp4 -vsync 0 -c:v libvpx-vp9 -crf 30 -b:v 0 -c:a copy VID_20191130_125715_vsync0_2.mp4 ffmpeg version n4.2.1 Copyright (c) 2000-2019 the FFmpeg developers
built with gcc 9.2.0 (GCC)
configuration: --prefix=/usr --disable-debug --disable-static --disable-stripping --enable-fontconfig --enable-gmp --enable-gnutls --enable-gpl --enable-ladspa --enable-libaom --enable-libass --enable-libbluray --enable-libdav1d --enable-libdrm --enable-libfreetype --enable-libfribidi --enable-libgsm --enable-libiec61883 --enable-libjack --enable-libmodplug --enable-libmp3lame --enable-libopencore_amrnb --enable-libopencore_amrwb --enable-libopenjpeg --enable-libopus --enable-libpulse --enable-libsoxr --enable-libspeex --enable-libssh --enable-libtheora --enable-libv4l2 --enable-libvidstab --enable-libvorbis --enable-libvpx --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxcb --enable-libxml2 --enable-libxvid --enable-nvdec --enable-nvenc --enable-omx --enable-shared --enable-version3
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
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 'VID_20191130_125715.mp4':
Metadata:
major_brand : mp42
minor_version : 0
compatible_brands: isommp42
creation_time : 2019-11-30T09:57:27.000000Z
location : <HIDDEN>
location-eng : <HIDDEN>
com.android.version: 9
Duration: 00:00:11.27, start: 0.000000, bitrate: 20733 kb/s
Stream #0:0(eng): Video: h264 (High) (avc1 / 0x31637661), yuv420p(tv, unknown/bt470bg/unknown), 1920x1080, 20031 kb/s, SAR 1:1 DAR 16:9, 29.98 fps, 30 tbr, 90k tbn, 180k tbc (default)
Metadata:
rotate : 90
creation_time : 2019-11-30T09:57:27.000000Z
handler_name : VideoHandle
Side data:
displaymatrix: rotation of -90.00 degrees
Stream #0:1(eng): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 128 kb/s (default)
Metadata:
creation_time : 2019-11-30T09:57:27.000000Z
handler_name : SoundHandle
Stream mapping:
Stream #0:0 -> #0:0 (h264 (native) -> vp9 (libvpx-vp9))
Stream #0:1 -> #0:1 (copy)
Press [q] to stop, [?] for help
[libvpx-vp9 @ 0x564718caf5c0] v1.8.1
Output #0, mp4, to 'VID_20191130_125715_vsync0_2.mp4':
Metadata:
major_brand : mp42
minor_version : 0
compatible_brands: isommp42
com.android.version: 9
location : <HIDDEN>
location-eng : <HIDDEN>
encoder : Lavf58.29.100
Stream #0:0(eng): Video: vp9 (libvpx-vp9) (vp09 / 0x39307076), yuv420p, 1080x1920 [SAR 1:1 DAR 9:16], q=-1--1, 30 fps, 15360 tbn, 30 tbc (default)
Metadata:
encoder : Lavc58.54.100 libvpx-vp9
creation_time : 2019-11-30T09:57:27.000000Z
handler_name : VideoHandle
Side data:
cpb: bitrate max/min/avg: 0/0/0 buffer size: 0 vbv_delay: -1
displaymatrix: rotation of -0.00 degrees
Stream #0:1(eng): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 128 kb/s (default)
Metadata:
creation_time : 2019-11-30T09:57:27.000000Z
handler_name : SoundHandle
frame= 338 fps=4.0 q=0.0 Lsize= 11511kB time=00:00:11.23 bitrate=8394.3kbits/s speed=0.132x
video:11324kB audio:176kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.093868%
$ mediainfo VID_20191130_125715.mp4 VID_20191130_125715_vsync0_2.mp4
General
Complete name : VID_20191130_125715.mp4
Format : MPEG-4
Format profile : Base Media / Version 2
Codec ID : mp42 (isom/mp42)
File size : 27.9 MiB
Duration : 11 s 273 ms
Overall bit rate : 20.7 Mb/s
Encoded date : UTC 2019-11-30 09:57:27
Tagged date : UTC 2019-11-30 09:57:27
xyz : <HIDDEN>
com.android.version : 9
Video
ID : 1
Format : AVC
Format/Info : Advanced Video Codec
Format profile : [email protected]
Format settings : CABAC / 1 Ref Frames
Format settings, CABAC : Yes
Format settings, Reference frames : 1 frame
Format settings, GOP : M=1, N=30
Codec ID : avc1
Codec ID/Info : Advanced Video Coding
Duration : 11 s 273 ms
Bit rate : 20.0 Mb/s
Width : 1 920 pixels
Height : 1 080 pixels
Display aspect ratio : 16:9
Rotation : 90°
Frame rate mode : Variable
Frame rate : 29.970 (29970/1000) FPS
Minimum frame rate : 25.395 FPS
Maximum frame rate : 30.090 FPS
Color space : YUV
Chroma subsampling : 4:2:0
Bit depth : 8 bits
Scan type : Progressive
Bits/(Pixel*Frame) : 0.322
Stream size : 26.9 MiB (97%)
Title : VideoHandle
Language : English
Encoded date : UTC 2019-11-30 09:57:27
Tagged date : UTC 2019-11-30 09:57:27
Color range : Limited
Color primaries : BT.601 PAL
mdhd_Duration : 11273
Codec configuration box : avcC
Audio
ID : 2
Format : AAC LC
Format/Info : Advanced Audio Codec Low Complexity
Codec ID : mp4a-40-2
Duration : 11 s 221 ms
Bit rate mode : Constant
Bit rate : 128 kb/s
Channel(s) : 2 channels
Channel layout : L R
Sampling rate : 48.0 kHz
Frame rate : 46.875 FPS (1024 SPF)
Compression mode : Lossy
Stream size : 176 KiB (1%)
Title : SoundHandle
Language : English
Encoded date : UTC 2019-11-30 09:57:27
Tagged date : UTC 2019-11-30 09:57:27
General
Complete name : VID_20191130_125715_vsync0_2.mp4
Format : MPEG-4
Format profile : Base Media
Codec ID : isom (isom/iso2/mp41)
File size : 11.2 MiB
Duration : 11 s 267 ms
Overall bit rate : 8 369 kb/s
Writing application : Lavf58.29.100
Video
ID : 1
Format : vp09
Codec ID : vp09
Duration : 11 s 267 ms
Bit rate : 8 234 kb/s
Width : 1 080 pixels
Height : 1 920 pixels
Display aspect ratio : 0.562
Frame rate mode : Constant
Frame rate : 30.000 FPS
Scan type : Progressive
Bits/(Pixel*Frame) : 0.132
Stream size : 11.1 MiB (98%)
Title : VideoHandle
Language : English
Audio
ID : 2
Format : AAC LC
Format/Info : Advanced Audio Codec Low Complexity
Codec ID : mp4a-40-2
Duration : 11 s 222 ms
Bit rate mode : Constant
Bit rate : 128 kb/s
Channel(s) : 2 channels
Channel layout : L R
Sampling rate : 48.0 kHz
Frame rate : 46.875 FPS (1024 SPF)
Compression mode : Lossy
Stream size : 176 KiB (2%)
Title : SoundHandle
Language : English
Default : Yes
Alternate group : 1