Changes between Version 59 and Version 60 of Encode/AAC

Timestamp:

Apr 21, 2023, 2:04:09 PM (3 years ago)

Author:

Mingye Wang

Comment:

Nevermind, _at is its own thing

Encode/AAC

@@ -3 +3 @@
 [[http://en.wikipedia.org/wiki/Advanced_Audio_Coding|Advanced Audio Coding (AAC)]] is the successor format to MP3, and is defined in MPEG-4 part 3 (ISO/IEC 14496-3). It is often used within an MP4 container format; for music the `.m4a` extension is customarily used. The second-most common use is within MKV (Matroska) files because it has better support for embedded text-based soft subtitles than MP4. The examples in this guide will use the extensions MP4 and M4A.
 
-FFmpeg supports two AAC-LC encoders (`aac` and `libfdk_aac`) and one HE-AAC (v1/2) encoder (`libfdk_aac`). The license of `libfdk_aac` is not compatible with GPL, so the GPL does not permit distribution of binaries containing incompatible code when GPL-licensed code is also included. Therefore this encoder have been designated as "non-free", and you cannot download a pre-built ffmpeg that supports it. This can be resolved by [[CompilationGuide|compiling ffmpeg]] yourself.
+FFmpeg supports three AAC-LC encoders (`aac`, `libfdk_aac`, `aac_at`) and two HE-AAC (v1/2) encoder (`libfdk_aac`, `aac_at`). The license of `libfdk_aac` is not compatible with GPL, so the GPL does not permit distribution of binaries containing incompatible code when GPL-licensed code is also included. Therefore this encoder have been designated as "non-free", and you cannot download a pre-built ffmpeg that supports it. This can be resolved by [[CompilationGuide|compiling ffmpeg]] yourself.
 
 See also [[Encode/HighQualityAudio]] for general guidelines on FFmpeg audio encoding (which also includes a comparison of which AAC encoder is best quality).
@@ -125 +125 @@
 By default, the native encoder produces AAC-LC, which is a "low complexity" profile of baseline AAC. It actually supports the more powerful "main" and "long-term prediction" profiles ([[https://ffmpeg.org/ffmpeg-codecs.html#aac|documentation]]), but these are less tested.
 
-The native encoder is actually two encoders in a trench-coat. When a build is configured with --enable-audiotoolbox, the libavcodec implementation is swapped out for Apple's audioToolbox.framework, normally available only on macOS. Apple's encoder is quite good in listening tests and has HE-AAC support, so that the same `-profile:a` flags work. You may have come across this implementation on other platforms as "QAAC" or "audioToolboxWrapper", but licensing issues for these modifications is too much for FFmpeg to deal with.
-
 === Examples ===
 
@@ -144 +142 @@
 Native FFmpeg AAC Encoder does not do CBR audio encoding.
 
-
+----
+= AudioToolbox =
+When a build is configured with --enable-audiotoolbox, Apple's audioToolbox.framework (normally available only on macOS) will provide a series of codecs suffixed `_at`. Apple's encoder is quite good in listening tests and has HE-AAC support, so that the same `-profile:a` flags from FDK work<!-- see audiotoolboxenc.c, ffat_get_format_id -->. You may have come across this implementation on other platforms as "QAAC" or "audioToolboxWrapper", but licensing issues for these modifications is too much for FFmpeg to deal with.
+
+----
 = Metadata =