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6th September 2021, 22:57 | #1 | Link |
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ffmpeg ac3 vs eac3 - any difference?
Hi.
I've been doing some encodes at different bitrates and ABX tests. My results show no audible improvement using EAC3 at the same bitrate compared to the supposedly less capable AC3. The difference do exist... but I had to phase invert and check cancellation to find it. So my question about EAC3 and ffmpeg's EAC3 is...
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7th September 2021, 02:59 | #2 | Link |
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What bitrates did you test?
I'm guessing it shold show some difference for music @ 64-160kps stereo, but I haven't done any tests for DDP myself. EBU testing https://tech.ebu.ch/docs/tech/tech3324.pdf (p21) has shown DDP 256kps almost matches DD 384kps on surround, but this is on professional encoders. |
7th September 2021, 06:02 | #3 | Link | |
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No difference that I can hear at least, after lots of ABX, comparing ffmpeg's AC3 vs. EAC3 at same birate. This implementation of EAC3 offers nothing like what that EBU test shown in 2007, rendering useless for my needs (5.1 channels). So I was wondering if someone can confirm my results... if someone here is using ffmpeg and not dolby encoder engine or similar commercial encoders. Last edited by bokeron2020; 7th September 2021 at 06:05. |
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7th September 2021, 10:31 | #6 | Link |
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Nope, is just quality comparation between 5.1 AC3 and EAC3 by ffmpeg.
Seems than ffmpeg only uses eac3 frames type 0 (eac3 independent, for that the bitrate is limited to 6144 Kb/s at 48 KHz, with 256 samples per frame with a max size of 4096 bytes). It not use dependent frames, for that is limited to 5.1 and others (more bitrate, channels and programs). And it not use frames type 2 (AC3 encoded) for that it can't be used for BD tracks than need embedded AC3. The question is if the EAC3 encoder have better quality at same size than AC3 like Dolby claim in their encoder.
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7th September 2021, 12:48 | #7 | Link | |
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7th September 2021, 15:12 | #8 | Link |
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Yeah, to hear much improvement with E-AC-3, you have to set the bitrate lower. In my view, it's not worth sacrificing AC-3's greater compatibility for a modest reduction in file-size and/or (at sane bitrates) a negligible increase in quality, especially given that ffmpeg's AC-3 encoder is so good these days. If you're interested only in playback via PC, you might as well use AAC instead.
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7th September 2021, 19:06 | #10 | Link | |
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I suppose a commercial encoder would fare a lot better at any given bitrate. AAC isn't well supported for multichannel audio in hardware players/decoders. I'm aiming for such compatibility... and I don't know where the market will go regarding AAC but Dolby/DTS are still dominant and churning out AC3/DTS centered tecghnologies. |
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7th September 2021, 19:22 | #12 | Link |
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If you mean EAC3 allows more than 5.1 channel... then that may be the only difference with AC3 in ffmpeg.
What I'm experiencing and testing is ffmpeg's EAC3 performing at roughly the same level of quality than AC3... and that should not be the case. EBU 2007 tests show DD+ being superior. So I'm here trying to find confirmation to my findings so I can be sure I am really hearing what I think I hear, ie, no difference. |
7th September 2021, 20:25 | #14 | Link | |
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- Beyerdynamic DT-1770 Pro headphones - Sabaj D5 DAC - foobar2000 ABX plugin - Audacity for phase cancellation check. - My ears: 10-16800Hz range @10dB, can ABX FLAC/Stereo MP3 @-V1 or CBR 256 / AC3 5.1 @ 640 from 448 (not easily, I mean, I can but I have to focus heavily on artifacts) Phase cancellation tests are objective. Subjectively speaking the objective results show no big difference. So my ABX tests and phase cancellation seem to point the same way. Last edited by bokeron2020; 7th September 2021 at 21:58. |
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7th September 2021, 20:29 | #15 | Link | |
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IIRC, AC-3 and E-AC-3 are not meant to be used below 192 kbps for 5.1 audio. That's meant for AC-4 according to a few things I read about it. You can try 224 or 320 kbps for both AC-3 and E-AC-3 @ 5.1. See if you spot something |
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7th September 2021, 20:59 | #16 | Link |
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The old AC3 encoder Sonic Foundry apply by default for 5.1, 48 KHz:
Code:
Bitrate Bandwidth Kb/s KHz ------- --------- 224 9.05 256 12.42 320 15.80 384 18.05 448 20.30 I can't recommend less than 384 Kb/s for 5.1
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7th September 2021, 21:40 | #17 | Link | |||
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As tebasuna51 just quoted, I tested 192, 256 and 384 kbps. My results show that, at every bitrate, EAC3 ≈ AC3 quality-wise. Quote:
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I tested with and without cutoff, though. Same settings, similar results from AC3 or EAC3. Therefore I can only conclude that while ffmpeg's AC3 may be close or equal to commercial encoders, their EAC3 is way behind. I don't have the knowledge to understand ffmpeg's source code so it would be great if someone who can could explain it or disprove it... and, complementary to this, someone who knows what the stance of the developers is about this codec could shed some light on why is apparently subpar yet. Last edited by bokeron2020; 7th September 2021 at 21:45. |
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7th September 2021, 22:25 | #18 | Link | |
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Exactly, which is why I mentioned AAC only in the context of playback via PC. For compatibility with stand-alone players, AC-3 is the way to go: 5.1@640kbps sounds so good that switching to E-AC3 isn't worth the modest space saving or quality improvement. AFAIK, ffmpeg's E-AC-3 encoder still doesn't produce BD-compatible encodes. |
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7th September 2021, 22:46 | #19 | Link |
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The main reason E-AC3 was added to FFmpeg was that it allows flexible bitrate values (including a higher maximum), and not just the pre-defined presets AC3 uses. New E-AC3 coding tools are not actually implemented, unless required by the bitstream.
Due to some coding improvements its minimally better then AC3 at any given bitrate, but probably not even measurable.
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8th September 2021, 00:21 | #20 | Link | |
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I suppose there are no plans to improve it as developers seem to have other priorities/interests. I'll use what's available then. |
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