From: Lynne <dev@lynne.ee>
To: FFmpeg development discussions and patches <ffmpeg-devel@ffmpeg.org>
Subject: Re: [FFmpeg-devel] [RFC PATCH 1/3] aacdec: always skip the first 2048 samples if there's no side data
Date: Tue, 12 Sep 2023 18:25:14 +0200 (CEST)
Message-ID: <Ne9CWDq--F-9@lynne.ee> (raw)
In-Reply-To: <AS8P250MB074484A0312A8401DBB6EF3D8FF1A@AS8P250MB0744.EURP250.PROD.OUTLOOK.COM>
Sep 12, 2023, 09:43 by andreas.rheinhardt@outlook.com:
> Lynne:
>
>> For some reason, this was never set, which meant all **raw** AAC in ADTS
>> streams, except faac, had extra samples at the start.
>>
>> Despite this being a standard MDCT-based codec with a frame size of 1024,
>> hence a delay of 1024 samples at the start, all major encoders, excluding
>> faac and FFmpeg, use 2048 samples of padding.
>>
>> The FFmpeg encoder will be modified to also output 2048 samples of padding
>> at the start, to make it in line with other encoders.
>>
>
> Does this also have actual advantages besides "being in line with other
> encoders"?
>
Not really. I don't have an opinion on this. 1024 is the natural
delay of the codec, so maybe it would be best to leave it at that.
>> Yes, this leaves FATE pretty sad. Will fix it with the real version of the patch.
>>
>
> Didn't we once guess the number of skip samples like this, only for this
> guesswork to be removed intentionally? (This is not a rhetorical
> question; I thought it to be true, but I see that there is still code
> for faac in decode_fill(); maybe I misremember.)
>
I don't remember something like that. The faac workaround dates back
from 2012 (bfe735b5824c7d10ba42932a17d786db50e3b2d4), and it's only for faac.
It's less of a guess, as most encoders to use the FIL extension to signal
themselves.
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next prev parent reply other threads:[~2023-09-12 16:25 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-09-12 6:10 Lynne
[not found] ` <Ne7-l4q--3-9@lynne.ee-Ne7-pA6----9>
2023-09-12 6:11 ` [FFmpeg-devel] [RFC PATCH 2/3] decode: allow decoders to override skip_samples Lynne
2023-09-12 6:14 ` [FFmpeg-devel] [RFC PATCH 3/3] aacdec: allow to skip sbr start-up delay Lynne
[not found] ` <Ne70gnX--3-9@lynne.ee-Ne70juu----9>
2023-09-12 6:15 ` Lynne
2023-09-12 7:10 ` [FFmpeg-devel] [RFC PATCH 1/3] aacdec: always skip the first 2048 samples if there's no side data Andreas Rheinhardt
2023-09-12 16:25 ` Lynne [this message]
2023-09-12 21:24 ` Thierry Foucu
2023-10-03 4:09 ` Lynne
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