Ensuring Precise 1-Second Audio File Splitting in GStreamer

Application Development
1

Hello,

I am trying to create an audio pipeline that precisely splits audio into raw aac 1-second files. Here is my current GStreamer pipeline:

gst-launch-1.0 -e audiotestsrc wave=4 is-live=true ! queue ! audio/x-raw, format=S16LE, layout=interleaved, rate=44100, channels=2 ! voaacenc ! aacparse ! audio/mpeg, mpegversion=4, stream-format=adts ! multifilesink location=a_temp%06d.aac next-file="max-duration" max-file-duration=1000000000

After examining the generated files, I noticed that they are not exactly 1 second long. Running ffprobe on one of the files shows that the duration is approximately 1.02 seconds instead of precisely 1 second.

ffprobe a_temp000002.aac

ffprobe result
ffprobe result1148×126 10.3 KB

ls -al --time-style=full-iso

Issue

Despite setting max-file-duration=1000000000 (1 second), the files exceed this duration.

Question

How can I modify my pipeline to ensure each file is exactly 1.00 seconds long?
Any insights or suggestions would be greatly appreciated!

2

AAC will (typically) encode frames of 1024 samples, so your chunk size will be a multiple of 1024 samples.

In your case it’s probably 44 frames at 1024 samples = 45056 samples, divided by 44100 samples per second = 1.021678005s

I think the only way to get exactly 1 second chunks is to find an AAC encoder that encodes 960 samples per frame in combination with a 48kHz sample rate.

I don’t think any of the libraries/encoders available in GStreamer can support that out of the box though.

1 Like
3

Hello,
@tpm Thank you for your insightful response. You are absolutely right.

After discussing with my team, we decided to implement this logic accordingly. I have rewritten the pipeline in Python and added a probe function connected to the last multifilesink element:

aac_multifilesink_sink_pad = aac_sink.get_static_pad("sink")
aac_multifilesink_sink_pad.add_probe(
            Gst.PadProbeType.BUFFER,
            audio_time_test_probe_function,
            logger,
            aac_sink
        )

total_packets = 0
frame_number = 0
previous_timestamp = 0

def audio_time_test_probe_function(pad: Gst.Pad, info: Gst.PadProbeInfo, logger: logging.Logger, aac_sink: Gst.Element) -> Gst.PadProbeReturn:
    global frame_number, previous_timestamp, total_packets

    gst_buffer = info.get_buffer()
    if not gst_buffer:
        logger.error("Unable to get GstBuffer for audio probe function")
        return Gst.PadProbeReturn.OK
    
    timestamp = gst_buffer.pts
    frame_stamp = 1 / (44100 / 1024) * 1000000000
    total_packets += 1

    if timestamp + frame_stamp > (frame_number + 1) * 1000000000:
        timeastmp_diff = timestamp - previous_timestamp
        logger.info(f"Saving file {frame_number} with timestamp {timestamp} | {timeastmp_diff} | {total_packets}")
        
        frame_number += 1
        previous_timestamp = timestamp
        total_packets = 0

    return Gst.PadProbeReturn.OK

I would like to trigger file saving inside the if statement. Given that the multifilesink element (aac_sink) is passed as a parameter to the function, how can I manually trigger file saving on multifilesink? I also thought about using splitmuxsink and running emit("split-now") however because of the mp4mux inside the splitmuxsink, it does not return raw aac files, but encapsulates them in mp4.