FFmpeg的AAC（“libfaac”）编解码器选项？ [英] FFmpeg's AAC ("libfaac") Codec Options?

问题描述

对于AAC（libfaac）音频编码器，如何通过FFmpeg的命令将MPEG版本指定为MPEG-4或MPEG-2？

For AAC ("libfaac") audio encoder, how can I specify the "MPEG Version" to either "MPEG-4" or "MPEG-2" through FFmpeg's command?

推荐答案

使用libfaac时，FFmpeg将MPEG版本硬编码为MPEG-4。你可以在 libfaac.c ，第118行观察。

When using libfaac, FFmpeg hard-codes the MPEG version to MPEG-4. You can observe this in libfaac.c, line 118.

faac_cfg->mpegVersion = MPEG4;

如果要更改它，您将下载FFmpeg源，修改此行以使用 MPEG2 ，并用适当的配置重新编译FFmpeg（包括 - enable-libfaac ）。这可以起作用并产生一个可播放的文件，但是您显然必须使用比特流筛选器来为MPEG-4容器创建有效的比特流：

If you want to change it, you will have download the FFmpeg source, modify this line to use MPEG2 instead, and recompile FFmpeg with the appropriate configuration (including --enable-libfaac). This works and produces a playable file, however you'll obviously have to use a bitstream filter to create a valid bitstream for MPEG-4 containers now:

ffmpeg -i in.wav -c:a libfaac -absf aac_adtstoasc out.m4a

如果您直接使用FAAC API，您可以根据需要更改此参数。

If instead you use the FAAC API directly, you can of course change this parameter as you wish.

理想情况下，一个将提交FFmpeg的补丁以包含一个新的选项，允许您手动设置，但是鉴于MPEG-4被选为硬编码的默认值，我看不到令人信服的理由来实现。

Ideally, one would submit a patch for FFmpeg to include a new option which allows you to set this manually, but given that MPEG-4 was chosen as a hardcoded default I don't see a compelling reason to implement this.

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