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I am trying to convert a DTS stream to AAC(stereo) using the following command:

ffmpeg -i "input.mkv" -c:v copy -c:a aac -q:a 2 -ac 2 -ar 48000 "output.mp4"

[ffmpeg version : 3.4.8]

Here q:a 2 controls the output bitrate or quality of the audio stream (VBR). In FFmpeg docs its effective range is given as 0.1-2 where 2 is the best quality. But I have tried increasing this number up to 5 or 6 and the bitrate of output stream keeps increasing.

So I want to know the best possible way to convert the DTS stream to AAC stream with the highest quality. For example, is there a number n such that q:n will set the highest quality conversion?

Thanks.

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  • The native AAC encoder goes upto ~260 kbps. Set it usising bitrate. Commented Mar 7, 2021 at 4:44
  • Thanks @Gyan I will try it using bitrate. Commented Mar 7, 2021 at 5:53
  • @Gyan I thought -b:a for the AAC encoder would enable CBR mode? Commented yesterday

1 Answer 1

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I'll assume you mean AAC-LC and not something like xHE-AAC (USAC).

With the highest quality? Use -c:a libfdk_aac and not -c:a aac. The quality of the native AAC encoder is poor. Control quality with -vbr which takes a value between 1 and 5. See HA wiki. Note that the FDK AAC encoder is not enabled in ffmpeg by default for copyright reasons.

If you happen to be on an Apple device, the Apple AAC encoder, -c:a aac_at, is even better.

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