FFmpeg AAC CBR

gwaugh

Is there a way using the Premiere / MediaEncoder plugin to use CBR AAC using the FFMpeg encoder? It seems to always produce VBR audio even if the video codec is set to CBR. For example, on one project the highest audio bitrate it will produce is 232Kb/s (according to FFmpeg -i) if you set it any higher than 192k.

The issue is our master control has a QC check that requires the audio bitrate to be > 300Kb/s and if the metadata says anything less it will fail the asset right away.

UPDATE:

According to this, AAC by default (-v 0) will be CBR:

http://wiki.hydrogenaud.io/index.php?titl…K_AAC#Bandwidth

Something else is going on here then… no matter what I set it to, any bitrate greater than 192Kb/s will result in the audio bitrate being 232Kb/s.

According to ffmpeg -I:

"Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 232 kb/s (default)"

Any ideas?

Vouk

So when I export like this ...

.. I get:

Code

Audio
ID                                       : 2
Format                                   : AAC LC
Format/Info                              : Advanced Audio Codec Low Complexity
Codec ID                                 : mp4a-40-2
Duration                                 : 8 s 438 ms
Duration_LastFrame                       : -10 ms
Bit rate mode                            : Constant
Bit rate                                 : 319 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                              : 329 KiB (4%)
Default                                  : Yes
Alternate group                          : 1

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which should be okay, right?

gwaugh

That's exactly how my export settings look. How can I see the "Code" view that you have above?

Vouk

Just install the "Media Info" tool.

gwaugh

Interesting... so it is doing VBR.

ID : 2

Format : AAC LC

Format/Info : Advanced Audio Codec Low Complexity

Codec ID : mp4a-40-2

Duration : 11 min 50 s

Bit rate mode : Variable

Bit rate : 233 kb/s

Maximum bit rate : 320 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 : 19.7 MiB (1%)

Default : Yes

Alternate group : 1

I thought I could add custom parameters into the encoder dialog but I guess not. Is there somewhere else I can look to force it to do CBR?

Vouk

According to the ffmpeg documentation:

https://www.ffmpeg.org/ffmpeg-codecs.html#Options-6

Zitat

b

Set bit rate in bits/s. Setting this automatically activates constant bit rate (CBR) mode. If this option is unspecified it is set to 128kbps.

it should be CBR.

gwaugh

Yeah, I did see that. But it's only making VBRs for me. How can I figure this out?

gwaugh

Here's the log file:

Code

[15:28:52] ---------------------------------------------
[15:28:52] Export started
[15:28:52] ---------------------------------------------
[15:28:52] Frame size:      1920x1080
[15:28:52] Pixel aspect:    1:1
[15:28:52] Frame rate:      29.97
[15:28:52] Interlaced:      No
[15:28:52] Color range:     tv
[15:28:52] Color space:     bt709
[15:28:52] Color primaries: bt709
[15:28:52] Color TRC:       bt709
[15:28:52] Sample rate:     48000
[15:28:52] Audio channels:  2
[15:28:52] ---------------------------------------------
[15:28:52] Opening codec: h264_nvenc with options: b=10000000|gpu=0|preset=hq|profile=high|rc=cbr
[15:28:52] Opening codec: aac with options: b=320000|profile=aac_low
[15:28:53] Requesting pixel format: yuv420p
[15:28:53] Frame #0: vRender: 118361 us, vProcess: 3 us, vEncoding: 2049 us, Latency: 120445 us
[15:28:53] Frame #1: vRender: 71245 us, vProcess: 3 us, vEncoding: 594 us, aRender: 27 us, aEncoding: 235 us, Latency: 152691 us
…
[15:47:38] Frame #63307: vRender: 73683 us, vProcess: 3 us, vEncoding: 984 us, aRender: 34 us, aEncoding: 1583 us, Latency: 133290 us
[15:47:38] Frame #63308: vRender: 19595 us, vProcess: 3 us, vEncoding: 957 us, aRender: 40 us, aEncoding: 130 us, Latency: 20742 us
[15:47:38] Exported 63308 frames in 1125 seconds. (avg. 56 fps)
[15:47:38] Flushing encoders and finalizing ...
[15:47:38] Video and audio buffers flushed.
[15:47:38] Trailer has been written.
[15:47:38] Closing encoders ...
[15:47:38] ---------------------------------------------
[15:47:38] Export finished
[15:47:38] ---------------------------------------------

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And it still did audio in VBR:

Code

Audio
ID                                       : 2
Format                                   : AAC LC
Format/Info                              : Advanced Audio Codec Low Complexity
Codec ID                                 : mp4a-40-2
Duration                                 : 35 min 12 s
Bit rate mode                            : Variable
Bit rate                                 : 219 kb/s
Maximum bit rate                         : 320 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                              : 55.1 MiB (2%)
Default                                  : Yes
Alternate group                          : 1

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Any ideas?

Vouk

What version are you using?

gwaugh

Version 2.2. Installed using installer-2.2.exe that I downloaded this morning. Should I try the 2.3 beta then?

Vouk

Please try, yes.

gwaugh

I tried beta4, and the same thing. However I did see something interesting. It appears that for bitrates 256Kb/s and up, it uses VBR however 192Kb/s and below it uses CBR.

128k log:

Code

[16:59:48] ---------------------------------------------
[16:59:48] Export started
[16:59:48] ---------------------------------------------
[16:59:48] Opening codec: libx264 with options:
[16:59:48] Opening codec: aac with options: b=128000|profile=aac_low
[16:59:48] ---------------------------------------------
[16:59:48] Frame size:      1920x1080
[16:59:48] Pixel aspect:    1:1
[16:59:48] Frame rate:      29.97
[16:59:48] Interlaced:      No
[16:59:48] Color range:     Limited
[16:59:48] Color space:     bt.709
[16:59:48] Passes:          1
[16:59:48] Sample rate:     48000 Hz
[16:59:48] Audio channels:  2

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128k Media Info:

Code

Audio
ID                                       : 2
Format                                   : AAC LC
Format/Info                              : Advanced Audio Codec Low Complexity
Codec ID                                 : mp4a-40-2
Duration                                 : 2 min 5 s
Duration_LastFrame                       : -16 ms
Bit rate mode                            : Constant
Bit rate                                 : 132 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                              : 1.95 MiB (4%)
Default                                  : Yes
Alternate group                          : 1

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192k log:

Code

[17:02:16] ---------------------------------------------
[17:02:16] Export started
[17:02:16] ---------------------------------------------
[17:02:16] Opening codec: libx264 with options:
[17:02:16] Opening codec: aac with options: b=192000|profile=aac_low
[17:02:16] ---------------------------------------------
[17:02:16] Frame size:      1920x1080
[17:02:16] Pixel aspect:    1:1
[17:02:16] Frame rate:      29.97
[17:02:16] Interlaced:      No
[17:02:16] Color range:     Limited
[17:02:16] Color space:     bt.709
[17:02:16] Passes:          1
[17:02:16] Sample rate:     48000 Hz
[17:02:16] Audio channels:  2

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192k Media Info:

Code

Audio
ID                                       : 2
Format                                   : AAC LC
Format/Info                              : Advanced Audio Codec Low Complexity
Codec ID                                 : mp4a-40-2
Duration                                 : 2 min 5 s
Duration_LastFrame                       : -16 ms
Bit rate mode                            : Constant
Bit rate                                 : 192 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                              : 2.85 MiB (6%)
Default                                  : Yes
Alternate group                          : 1

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256k log:

Code

[17:15:34] ---------------------------------------------
[17:15:34] Export started
[17:15:34] ---------------------------------------------
[17:15:34] Opening codec: libx264 with options:
[17:15:34] Opening codec: aac with options: b=256000|profile=aac_low
[17:15:34] ---------------------------------------------
[17:15:34] Frame size:      1920x1080
[17:15:34] Pixel aspect:    1:1
[17:15:34] Frame rate:      29.97
[17:15:34] Interlaced:      No
[17:15:34] Color range:     Limited
[17:15:34] Color space:     bt.709
[17:15:34] Passes:          1
[17:15:34] Sample rate:     48000 Hz
[17:15:34] Audio channels:  2

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256k Media Info:

Code

Audio
ID                                       : 2
Format                                   : AAC LC
Format/Info                              : Advanced Audio Codec Low Complexity
Codec ID                                 : mp4a-40-2
Duration                                 : 2 min 5 s
Duration_LastFrame                       : -16 ms
Bit rate mode                            : Variable
Bit rate                                 : 211 kb/s
Maximum bit rate                         : 256 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                              : 3.14 MiB (6%)
Default                                  : Yes
Alternate group                          : 1

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Does that give any clues?

Vouk

I don't make any differences in the code about various bitrates. Did you this with FFmpeg on the command line?

Kleinrotti

I'm currently using Voukoder R2 2.2 and I also tried to reproduce this behavior. In my case I can confirm that, if I choose a bitrate higher than 256 kb/s with stereo sound MediaInfo says it is VBR. When using 5.1 Mediainfo says VBR no matter which bitrate I choose. But I think this is not a Voukoder problem because with ffmpeg commandline this is the same.

gwaugh

It's almost like Ffmpeg tries to optimize and makes a decision, based on the source audio, whether or not VBR will more efficient and override your settings. As in, it's concludes that anything more than a certain amount for that audio will make no difference so goes with the method that's the lower of the two. This could explain why we are all seeing different numbers since we're using different test files. Ours are a lot of spoken word.

Is there a way to use a different encoder (like Fraunhaufer) that will always do CBR? I saw in an earlier thread that was possible on the 1.x branch so wondering if it can be done on 2.2?

I really want to use and support this plug in as it would really make our workflow much more efficient. Just need to figure out a solution for this audio bitrate since QC will only accept it if audio is 320k...

Kleinrotti

You can use fdk_aac with Voukoder R2 too. You need the libfdk-aac-2.dll.

gwaugh

Great news! Using the fdk_aac for audio worked perfectly to create a 320Kb/s CBR. I sent the Voukoder-processed file to QC and it passed perfectly.

This is a great plugin and will save us a lot of time!

Vouk

I am happy to hear that!

FFmpeg AAC CBR

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