Detect BPM using ffmpeg/soundstretch

[jooola]

The analyzer could analyze bpm for those who need it, I have a working script below:

soundstrech is based on the soundtouch library which seem broadly used.

We simply need to convert the audio files to pcm and we can analyze it using soundstretch.

I will propose a Draft PR soon with this new analyzer. But I will probably do some large changes to the analyzer so it won't land in v3.

#!/usr/bin/env python3

from subprocess import run
from tempfile import TemporaryDirectory
import re

from pathlib import Path

src = Path("python_apps/airtime_analyzer/tests/fixtures/s1.flac")


with TemporaryDirectory() as tmp:
    tmp = Path(tmp)
    tmp.mkdir(exist_ok=True)
    tmp_file = tmp / "file.wav"

    result = run(
        ["ffmpeg", "-i", src, "-acodec", "pcm_s16le", "-f", "wav", tmp_file],
        capture_output=True,
        universal_newlines=True,
        check=True,
    )
    result.check_returncode()

    result = run(
        ["soundstretch", tmp_file, "-bpm"],
        capture_output=True,
        universal_newlines=True,
        check=True,
    )

    track_bpm_match = re.search(
        r"Detected BPM rate ([0-9]+\.[0-9]+)",
        result.stderr,
    )

    if track_bpm_match:
        print(float(track_bpm_match.group(1)))

Ref: http://www.surina.net/soundtouch/

[zklosko]

Two thoughts:

1. The last stable release of Soundtouch came out almost three years ago. Does the project still have enough life left in it for a longer-aiming project like ours?
2. Needing to convert a track to PCM just to analyze BPM doesn't seem like a worthwhile trade, especially since we're making broadcasting software and not DJ software. Some of our users (read: us) use Libretime for playout of full, 2 hour shows, which wouldn't have a consistent BPM to analyze, making the conversion a waste of computing resources on a live production server.

[jooola]

1. The last stable release of Soundtouch came out almost three years ago. Does the project still have enough life left in it for a longer-aiming project like ours?

I am confident that the soundtouch library will be working for age, the project using it would not let it die (https://www.surina.net/soundtouch/applications.html). If the soundstretch binary is not the right tool for us, we could pick another one or create our own. But I don't see any problem at the moment.

2. Needing to convert a track to PCM just to analyze BPM doesn't seem like a worthwhile trade, especially since we're making broadcasting software and not DJ software. Some of our users (read: us) use Libretime for playout of full, 2 hour shows, which wouldn't have a consistent BPM to analyze, making the conversion a waste of computing resources on a live production server.

I agree that getting BPM from a 2 hour show, or 1 hour audio mix doesn't make much sens, this is more useful when working with a lot of music tracks, so this could simply be limited to music tracks smaller than 15 minutes (should be configurable).

I am no expert, but I thought that bpm detection software would need to work with raw audio anyway ? We are are just seeing this step compared to other software.

[paddatrapper]

I agree that getting BPM from a 2 hour show, or 1 hour audio mix doesn't make much sens, this is more useful when working with a lot of music tracks, so this could simply be limited to music tracks smaller than 15 minutes (should be configurable).

Or tracks uploaded as a specific track type (default to Music)

[jooola]

Also, ideally the bpm detection should be done while tagging the audio library before upload, so we could also skip track with existing BPM tags. But I think the feature is nice-to-have.

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