2

When doing:

youtube-dl -xf bestaudio/best <link to playlist>

...I get a lot of OPUS files at relatively "normal" bitrates like 130kbps.

However, when I run the same command with the additional stage of transcoding the downloaded OPUS files to AAC/M4A, using either one of the following commands:

youtube-dl -xf bestaudio/best --audio-format m4a <link to playlist>

youtube-dl -xf bestaudio[abr<=192] --audio-format m4a <link to playlist>

...the converted M4A files have much higher bitrates (and file sizes) than the original OPUS files, averaging more than 400kbps. This is more than a 300% increase in bitrate. Is this a bug with the post-processing stage of youtube-dl, or is it expected behaviour?

Is the only way to convert OPUS to an equivalent quality AAC file to give it a much higher bitrate? If so, does this mean that when I convert an OPUS file at, for example, 192k to AAC at 192k, that I'm losing a huge amount of quality?

Improve this question
2
  • The bitrate of any lossy transcoding step is dependent on how much data you are willing to loose and it is up to you what bitrate you want. Chances are you can choose a lower bitrate and you will still get something equivalent to your original source without much loss, but higher bitrates will obviously be more representative of the Opus decoder output while losing less data. How much quality is lost is difficult to define as the encoders function very differently and perceived quality differs from person to person.
    – Mokubai ♦
    Commented Mar 24, 2019 at 17:47
  • @Mokubai So the answer to my question is yes? Setting my M4A files at a high bitrate is the only way FFmpeg can create an equivalent quality file to the original OPUS?
    – Hashim Aziz
    Commented Mar 24, 2019 at 22:10

1 Answer 1

Reset to default
-1

Do not convert YouTube downloads to M4A/AAC. YouTube already offers AAC audio, just download that without reencoding.

A bitrate of over 400 kbps is obscenely high for AAC. With a decent encoder (FDK-AAC/qaac) 160-192 kbps should be enough to get on the same quality level as libopus 128 kbps vbr.

Reencoding relatively low quality lossy media is generally not recommended, because generation loss exists, you'll need a much higher bitrate to not add additional compression artifacts.

Improve this answer
1

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .