AV1 encoding to IVF

[Dendraspis]

Hello rigaya,

I have an issue when encoding to AV1. Until now NVEncC created an .av1 file that was muxed to MKV/MP4. Due to a bug and to be compliant with the other encoders, I decided to switch the extension to .ivf which is the sort of default extension for AV1 encoders. This is also supported by NVEncC, but the result is broken. Maybe I am missing something or is it a bug?

Little addition: It should also affect QSVEncC and VCEEncC.

Source File

```

General
Complete name            : A:\_StaxRip-Test\XXX.mkv
Format                   : Matroska
Format version           : Version 4
File size                : 17.5 MiB
Duration                 : 3 min 33 s
Overall bit rate         : 686 kb/s
Frame rate               : 25.000 FPS
Writing application      : Lavf58.35.100
Writing library          : Lavf58.35.100
ErrorDetectionType       : Per level 1

Video
ID                       : 1
Format                   : VP9
Format profile           : 0
Codec ID                 : V_VP9
Duration                 : 3 min 33 s          <===
Width                    : 1 920 pixels
Height                   : 1 080 pixels
Display aspect ratio     : 16:9
Frame rate mode          : Constant
Frame rate               : 25.000 FPS          <===
Color space              : YUV
Chroma subsampling       : 4:2:0
Bit depth                : 8 bits
Language                 : English
Default                  : Yes
Forced                   : No
Color range              : Limited
Color primaries          : BT.709
Transfer characteristics : BT.709
Matrix coefficients      : BT.709

Audio
ID                       : 2
Format                   : AAC LC
Format/Info              : Advanced Audio Codec Low Complexity
Codec ID                 : A_AAC-2
Duration                 : 3 min 33 s
Channel(s)               : 2 channels
Channel layout           : L R
Sampling rate            : 44.1 kHz
Frame rate               : 43.066 FPS (1024 SPF)
Compression mode         : Lossy
Title                    : ISO Media file produced by Google Inc.
Language                 : English
Default                  : Yes
Forced                   : No
```

---

Without altering the fps using this command line:
NVEncC64.exe --avsdll [..]\AviSynth.dll --qvbr 28 --codec av1 --preset P1 --output-depth 10 --colormatrix bt709 --colorprim bt709 --transfer bt709 -i XXX_AV1.avs -o XXX_AV1_out.av1

...NVEncC outputs the right values:

Output Info    AV1 main 10bit @ Level auto
               1920x1080p 0:0 25.000fps (25/1fps)

... and the media info is okay, even the fps are not mentioned, and the playback is also okay:

AV1 File

```

General
Count                                    : 349
Count of stream of this kind             : 1
Kind of stream                           : General
Kind of stream                           : General
Stream identifier                        : 0
Complete name                            : .\XXX_AV1_out.av1
Folder name                              : .
File name extension                      : XXX_AV1_out.av1
File name                                : XXX_AV1_out
File extension                           : av1
File size                                : 27374358
File size                                : 26.1 MiB
File size                                : 26 MiB
File size                                : 26 MiB
File size                                : 26.1 MiB
File size                                : 26.11 MiB
Stream size                              : 27374358
Stream size                              : 26.1 MiB (100%)
Stream size                              : 26 MiB
Stream size                              : 26 MiB
Stream size                              : 26.1 MiB
Stream size                              : 26.11 MiB
Stream size                              : 26.1 MiB (100%)
Proportion of this stream                : 1.00000

```

---

But when using the same command line with an .ivf file extension, NVEncC is also right:

Output Info    AV1 main 10bit @ Level auto
               1920x1080p 0:0 25.000fps (25/1fps)
               avwriter: av1 => ivf

... but the result is completely off, indicating 100 fps instead of 25, which leads to massive issues when mixing with audio to MKV/MP4:

IVF File

```

General
Complete name                            : .\XXX_AV1_out.ivf
Format                                   : IVF
File size                                : 26.2 MiB
Duration                                 : 53 s 420 ms
Overall bit rate                         : 4 109 kb/s
Frame rate                               : 100.000 FPS

Video
Format                                   : AV1
Format/Info                              : AOMedia Video 1
Codec ID                                 : AV01
Duration                                 : 53 s 420 ms          <===
Bit rate                                 : 4 099 kb/s
Width                                    : 1 920 pixels
Height                                   : 1 080 pixels
Display aspect ratio                     : 16:9
Frame rate                               : 100.000 FPS          <===
Bits/(Pixel*Frame)                       : 0.020
Stream size                              : 26.1 MiB (100%)

```

[rigaya]

It seems like that ivf format requires it's timebase of the stream to be as exact inverse of framerate, it's little weird behavior.

I'll have it changed in the next release, but I recommend to avoid use of ivf format, as "setting timebase to exact inverse of framerate" means that it cannot handle VFR (variable framerate) properly, and can only handle CFR (constant framerate).

I recommend to output video in mkv or mp4 format, which can handle timestamps more precisely. You shall be able to mux audio afterwards even if the video is in mkv or mp4 format.

[Dendraspis]

Oh, okay, very interesting and truly weird.

So I will avoid IVF and find another way and see, if I can implement a workflow with an MKV or MP4 file.

Thank you.