[FFmpeg-user] Bug in FFMPEG Alsa?

christina zou zou.christina at gmail.com
Sun Feb 19 11:15:15 EET 2017


You're right. The 3Mbps speed is as expected.

However, this still doesn't explain why my FFmpeg command requires 95% of
my device's CPU to record raw audio audio, when the equivalent Arecord
command takes 5% of my CPU.

Again, here are my two commands:

arecord -v -r48000 -c2 -fS32_LE --period-size=16384
--buffer-size=65536 -Dmic_sv -twav /dev/null

ffmpeg -f alsa -acodec pcm_s32le -i mic_sv -c copy -f null -

On Sat, Feb 18, 2017 at 12:38 PM, Moritz Barsnick <barsnick at gmx.net> wrote:

> On Fri, Feb 17, 2017 at 20:56:25 -0800, christina zou wrote:
> > 2. My ALSA bitrate is shown as 3072 kbps. This seems high - I only have a
> > Pi Zero. Is this a value I can manually set?
> Why is that high and why should a Pi not be able to handle a standard
> audio stream? 32 bits per sample, 48000 samples per second, two
> channels, that makes exactly 3072000 bits per second. There's nothing
> that can (or should) be done about that, that's how uncompressed audio
> works.
> If you can get your ALSA device to output less bts per sample, or less
> samples per second, you can reduce that rate, but I still don't
> understand why.
> Moritz
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