出于好奇，我检查了两个版本的视频文件，这两个版本没有重新编码，只是重新混合。我原本预计 ssim 分数为 1.0。相反，我看到的分数小于 1.0。
如何重复：
首先，重新混合视频：
MP4Box -cat video.mp4 -new test-1.mp4
-或者-
mkvmerge -o test-2.mkv video.mp4
现在，我希望这三个文件的质量 100% 相同。但是当我使用 ffmpeg 用 ssim 检查其中任意两个文件时，我得到了如下结果：
[Parsed_ssim_0 @ 0x7413a0] SSIM Y:0.899826 U:0.994930 V:0.994679 All:0.931486 (11.642182)
那么，到底发生了什么？为什么这三个文件在相互测试时没有获得 1.0 的 ssim 分数？这对我实际重新编码的视频获得的 ssim 分数有何影响？
ffmpeg：ffmpeg version 2.8.14-0ubuntu0.16.04.1
//// 编辑：添加实际的终端命令和输出：
exiftool video.mp4
ExifTool Version Number : 10.10
File Name : video.mp4
Directory : .
File Size : 10 MB
File Modification Date/Time : 2018:07:02 02:08:41+12:00
File Access Date/Time : 2018:07:02 02:09:09+12:00
File Inode Change Date/Time : 2018:07:02 02:09:04+12:00
File Permissions : rw-r--r--
File Type : MP4
File Type Extension : mp4
MIME Type : video/mp4
Major Brand : MP4 Base Media v1 [IS0 14496-12:2003]
Minor Version : 0.2.0
Compatible Brands : isom, iso2, mp41
Movie Data Size : 10427101
Movie Data Offset : 44
Movie Header Version : 0
Create Date : 0000:00:00 00:00:00
Modify Date : 0000:00:00 00:00:00
Time Scale : 1000
Duration : 0:01:01
Preferred Rate : 1
Preferred Volume : 100.00%
Preview Time : 0 s
Preview Duration : 0 s
Poster Time : 0 s
Selection Time : 0 s
Selection Duration : 0 s
Current Time : 0 s
Next Track ID : 3
Track Header Version : 0
Track Create Date : 0000:00:00 00:00:00
Track Modify Date : 0000:00:00 00:00:00
Track ID : 1
Track Duration : 0:01:01
Track Layer : 0
Track Volume : 0.00%
Image Width : 1920
Image Height : 1100
Graphics Mode : srcCopy
Op Color : 0 0 0
Compressor ID : hev1
Source Image Width : 1920
Source Image Height : 1100
X Resolution : 72
Y Resolution : 72
Bit Depth : 24
Video Frame Rate : 30
Matrix Structure : 1 0 0 0 1 0 0 0 1
Media Header Version : 0
Media Create Date : 0000:00:00 00:00:00
Media Modify Date : 0000:00:00 00:00:00
Media Time Scale : 44100
Media Duration : 0:01:01
Media Language Code : und
Handler Description : SoundHandler
Balance : 0
Audio Format : mp4a
Audio Channels : 2
Audio Bits Per Sample : 16
Audio Sample Rate : 44100
Handler Type : Metadata
Handler Vendor ID : Apple
Encoder : Lavf56.40.101
Avg Bitrate : 1.36 Mbps
Image Size : 1920x1100
Megapixels : 2.1
Rotation : 0
重新混合文件：
MP4Box -cat video.mp4 -new test-1.mp4
Appending file video.mp4 No suitable destination track found - creating new one (type vide)
No suitable destination track found - creating new one (type soun)
Saving test-1.mp4: 0.500 secs Interleaving
使用 ffmpeg/ssim 比较这两个文件：
ffmpeg -hide_banner -i video.mp4 -i test-1.mp4 -filter_complex "ssim" -f null -
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'video.mp4':
Metadata:
major_brand : isom
minor_version : 512
compatible_brands: isomiso2mp41
title : Intro
encoder : Lavf56.40.101
Duration: 00:01:01.14, start: 0.000000, bitrate: 1376 kb/s
Stream #0:0(und): Video: hevc (Main) (hev1 / 0x31766568), yuv420p(tv), 1920x1100, 1236 kb/s, 30 fps, 30 tbr, 16k tbn, 30 tbc (default)
Metadata:
handler_name : VideoHandler
Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 127 kb/s (default)
Metadata:
handler_name : SoundHandler
[mov,mp4,m4a,3gp,3g2,mj2 @ 0x24117e0] multiple edit list entries, a/v desync might occur, patch welcome
Last message repeated 1 times
Input #1, mov,mp4,m4a,3gp,3g2,mj2, from 'test-1.mp4':
Metadata:
major_brand : isom
minor_version : 1
compatible_brands: isom
creation_time : 2018-07-01 14:09:09
Duration: 00:01:01.14, start: 0.000000, bitrate: 1372 kb/s
Stream #1:0(und): Video: hevc (Main) (hev1 / 0x31766568), yuv420p(tv), 1920x1100, 1236 kb/s, 30 fps, 30 tbr, 44100 tbn, 30 tbc (default)
Metadata:
handler_name : VideoHandler
Stream #1:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 128 kb/s (default)
Metadata:
handler_name : SoundHandler
Output #0, null, to 'pipe:':
Metadata:
major_brand : isom
minor_version : 512
compatible_brands: isomiso2mp41
title : Intro
encoder : Lavf56.40.101
Stream #0:0: Video: rawvideo (I420 / 0x30323449), yuv420p, 1920x1100, q=2-31, 200 kb/s, 30 fps, 30 tbn, 30 tbc (default)
Metadata:
encoder : Lavc56.60.100 rawvideo
Stream #0:1(und): Audio: pcm_s16le, 44100 Hz, stereo, s16, 1411 kb/s (default)
Metadata:
handler_name : SoundHandler
encoder : Lavc56.60.100 pcm_s16le
Stream mapping:
Stream #0:0 (hevc) -> ssim:main (graph 0)
Stream #1:0 (hevc) -> ssim:reference (graph 0)
ssim (graph 0) -> Stream #0:0 (rawvideo)
Stream #0:1 -> #0:1 (aac (native) -> pcm_s16le (native))
Press [q] to stop, [?] for help
[null @ 0x24d47c0] Encoder did not produce proper pts, making some up.
frame= 1834 fps= 54 q=-0.0 Lsize=N/A time=00:01:01.13 bitrate=N/A
video:172kB audio:10532kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: unknown
[Parsed_ssim_0 @ 0x23f90c0] SSIM Y:0.893099 U:0.994654 V:0.994361 All:0.926902 (11.360919)
这是我没想到的部分：
SSIM Y:0.893099 U:0.994654 V:0.994361 All:0.926902
答案1
原因如下：
multiple edit list entries, a/v desync might occur, patch welcome
我建议使用
ffmpeg -hide_banner -ignore_editlist 1 -i video.mp4 -ignore_editlist 1 -i test-1.mp4
-filter_complex "[0]setpts=N/30/TB[a];[1]setpts=N/30/TB[b];[a][b]ssim" -f null -