ffmpeg:每块刷新输出文件 [英] ffmpeg: flushing output file every chunk

问题描述

我正在使用ffmpeg实时生成正弦音调，持续10秒钟.不幸的是，ffmpeg似乎很少每隔几秒钟刷新一次输出文件.我希望它每2048个字节刷新一次(= 2个字节的样本宽度* 1024个样本，我的自定义块大小).

I'm using ffmpeg to generate a sine tone in real time for 10 seconds. Unfortunately, ffmpeg seems to flush the output file only rarely, every few seconds. I'd like it to flush every 2048 bytes (=2bytes sample width*1024 samples, my custom chunk size).

以下脚本的输出:

import os
import time
import subprocess

cmd = 'ffmpeg -y -re -f lavfi -i "sine=frequency=440:duration=10" -blocksize 2048 test.wav'    

subprocess.Popen(cmd, shell=True)

time.sleep(0.1)
while True:
    print(os.path.getsize("test.wav"))
    time.sleep(0.1)

看起来像:

[...]
78
78
78
262222
262222
262222
[...]

使用#ffmpeg IRC的用户建议使用

A user on the #ffmpeg IRC proposed using

ffmpeg -re -f lavfi -i "sine=frequency=1000:duration=10" -f wav pipe: > test.wav

有效.但是，仅使用ffmpeg就能实现吗?

which works. But can this be achieved just using ffmpeg?

推荐答案

为了输出到文件，ffmpeg等待写入之前填充256 KiB的缓冲区.

For output to a file, ffmpeg waits to fill a buffer of 256 KiB before a write.

您可以使用flush_packets禁用该行为.

You can disable that behaviour, using flush_packets.

ffmpeg -y -re -f lavfi -i "sine=f=440:d=10" -blocksize 2048 -flush_packets 1 test.wav

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