[FFmpeg-user] eac3 encoding

[Mike Brown]

I just started digging into eac3 encoding and have been googling this and
that and have come up with:

ffmpeg -i front_left.wav -i front_right.wav -i front_center.wav -i lfe.wav \
-i back_left.wav -i back_right.wav \
-filter_complex "[0:a][1:a][2:a][3:a][4:a][5:a]amerge=inputs=6[aout]" \
-map "[aout]" -acodec eac3 -ab 999k outputfile.ac3

What I haven't been able to find are the available bitrates for eac3.
Obviously the normal ac3 bitrates up through 640kbps, but I do not know
what is available higher than that. The 999k above is just a place holder.

Thanks.

MB
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[Moritz Barsnick]

Post by Mike Brown
What I haven't been able to find are the available bitrates for eac3.
Obviously the normal ac3 bitrates up through 640kbps, but I do not know
what is available higher than that. The 999k above is just a place holder.

I don't see any restriction in the code, and the standard doesn't seem
to imply any restriction either:

What is the full range of data rates for Dolby Digital Plus?

Dolby Digital Plus can scale from 32 kbps all the way up to 6 Mbps. A
typical range for Dolby Digital Plus on high-definition optical discs
is 768 kbps to 1.5 Mbps.

(From
https://www.dolby.com/uploadedFiles/Assets/US/Doc/Professional/dolby-digital-plus-faq.pdf)

Moritz
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[Mike Brown]

Post by Moritz Barsnick

Post by Mike Brown
What I haven't been able to find are the available bitrates for eac3.
Obviously the normal ac3 bitrates up through 640kbps, but I do not know
what is available higher than that. The 999k above is just a place holder.

I don't see any restriction in the code, and the standard doesn't seem
What is the full range of data rates for Dolby Digital Plus?
Dolby Digital Plus can scale from 32 kbps all the way up to 6 Mbps. A
typical range for Dolby Digital Plus on high-definition optical discs
is 768 kbps to 1.5 Mbps.
(From
https://www.dolby.com/uploadedFiles/Assets/US/Doc/Professional/dolby-digital-plus-faq.pdf)

Thanks. I failed to look at dolby.com, but still needed to know if there
were any restrictions in the code.

MB
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[Moritz Barsnick]

Post by Mike Brown

Post by Moritz Barsnick
I don't see any restriction in the code, and the standard doesn't seem

Thanks. I failed to look at dolby.com, but still needed to know if there
were any restrictions in the code.

Sorry, I failed to see the restriction. ffmpeg will tell you if you
happen to enter an illegal one:

At 48k samplerate:
[eac3 @ 0xbe08920] invalid bit rate. must be 3008 to 6144000 for this sample rate
At 44.1k samplerate:
[eac3 @ 0xb9f3b40] invalid bit rate. must be 2768 to 5644800 for this sample rate

The actual formula is:
max_br = 2048 * s->sample_rate / frame_samples * 16;
min_br = ((s->sample_rate + (frame_samples-1)) / frame_samples) * 16;

I assume it is a restriction of the codec (of how it is defined), not
of the encoder.

Moritz
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[Mike Brown]

Post by Moritz Barsnick
Sorry, I failed to see the restriction. ffmpeg will tell you if you

3kbps? Your previous email mention the Dolby spec going down to 32kbps.

Not that it makes a difference, as I would never go that low. I'd just use
ac3 for bitrates of 640kbps and lower.

Thanks for the update.

MB
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