Apakah ssim ffmpeg tidak melakukan apa yang seharusnya dilakukan?

Hanya karena penasaran, saya memeriksa dua versi file video yang TIDAK di-encode, hanya di-muxed. Saya mengharapkan skor ssim menjadi 1,0. Sebaliknya, saya melihat skor <1,0.

Bagaimana cara mengulang:

Pertama, lakukan mux-ulang video:

MP4Box -cat video.mp4 -new test-1.mp4

-atau-

mkvmerge -o test-2.mkv video.mp4

Sekarang, saya berharap bahwa ketiga file tersebut menjadi 100% identik dalam hal kualitas. Tetapi ketika saya menggunakan ffmpeg untuk memeriksa mereka berdua dengan ssim, saya mendapatkan sesuatu seperti ini:

[Parsed_ssim_0 @ 0x7413a0] SSIM Y:0.899826 U:0.994930 V:0.994679 All:0.931486 (11.642182)

Jadi apa yang terjadi? Mengapa ketiga file ini tidak mendapatkan skor ssim 1,0, saat diuji satu sama lain? Bagaimana ini memengaruhi skor ssim yang saya dapatkan dengan video yang sebenarnya disandikan ulang?

ffmpeg: ffmpeg version 2.8.14-0ubuntu0.16.04.1

//// Edit: Menambahkan perintah dan output terminal aktual:

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

mux-ulang file:

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

Bandingkan dua file dengan ffmpeg / ssim:

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)

Ini adalah bagian yang saya tidak harapkan: SSIM Y:0.893099 U:0.994654 V:0.994361 All:0.926902

Inilah penyebabnya: multiple edit list entries, a/v desync might occur, patch welcome

Saya sarankan menggunakan

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 -