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Topic: freeformat- how I can create mp3 @ 384kbps? (Read 2017 times) previous topic - next topic - Topic derived from freeformat at 640 kbp...
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Re: freeformat- how I can create mp3 @ 384kbps?

Reply #25
The only way for a stream parser to recognize Free Format properly is to blindly search ahead for the sync word, since there is no other way to detect the length of a packet, other than completely parsing it.

Re: freeformat- how I can create mp3 @ 384kbps?

Reply #26
The only way for a stream parser to recognize Free Format properly is to blindly search ahead for the sync word, since there is no other way to detect the length of a packet, other than completely parsing it.
Theoretically, if we store it in a proper container such as mp4, each frame can be externally delimited on the container side.
ffmpeg recognizes and decodes all of the free format MP3s. Really, player decoders are behind on this. I expected more from MPC-HC.
Well, which version of ffmpeg have you tried?
I just tried with lame --freeformat -b 384, but ffmpeg (version 4.1.4) cannot decode the resulting file.
According to a comment in the libavcodec source (mpegaudio_template.c), they are aware of the free format.
However, when bitrate_index in the frame header is zero, decode_frame() of the decoder just returns an error.
Since this check is in the decoder, ffmpeg won't be able to handle freeformat mp3 even when stored in containers such as mp4.

Re: freeformat- how I can create mp3 @ 384kbps?

Reply #27
Huh. I was under the impression that it was ffmpeg under Audacity that loaded free format.

Through process of elimination, and checking the source code, it appears that Audacity's built-in MP3 decoder(s) is handling it.

 
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