如何使用 FFMPEG 全长将 AAC/MP4A 转换为 MP3？ 音频文件在 1 秒后被切断

Question

I have recorded an audio file with MediaRecorder on iPhone. Here is a copy of an example:https://github.com/q2apro/shared/blob/main/18380889311644327118 (click on download)

As ffmpeg command I am using:

ffmpeg -i 18380889311644327118 -ar 44100 -ac 2 -b:a 128k -c:a libmp3lame -q:a 0 18380889311644327118.mp3

-i specifies the input file
-vn disables all video-streams from the input
-ar audio sampling frequency
-ac number of audio channels
-b:a bit rate
-c:a libmp3lame - codec of target file
-q:a quality set audio quality (codec-specific) (lower is better), see https://superuser.com/a/1515841

-sn disables all subtitle-streams from the input
-dn disables all data-streams from the input

The console output looks like this:

Input #0, mov,mp4,m4a,3gp,3g2,mj2, from '18380889311644327118':
  Metadata:
    major_brand     : iso5
    minor_version   : 1
    compatible_brands: isomiso5hlsf
    creation_time   : 2021-12-08T15:44:06.000000Z
  Duration: 00:00:01.00, start: 0.000000, bitrate: 2258 kb/s
    Stream #0:0(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, mono, fltp, 2234 kb/s (default)
    Metadata:
      creation_time   : 2021-12-08T15:44:06.000000Z
      handler_name    : Core Media Audio
Stream mapping:
  Stream #0:0 -> #0:0 (aac (native) -> mp3 (libmp3lame))

Output #0, mp3, to '18380889311644327118.mp3':
  Metadata:
    major_brand     : iso5
    minor_version   : 1
    compatible_brands: isomiso5hlsf
    TSSE            : Lavf58.29.100
    Stream #0:0(und): Audio: mp3 (libmp3lame), 44100 Hz, stereo, fltp, 128 kb/s (default)
    Metadata:
      creation_time   : 2021-12-08T15:44:06.000000Z
      handler_name    : Core Media Audio
      encoder         : Lavc58.54.100 libmp3lame
size=      17kB time=00:00:01.01 bitrate= 135.5kbits/s speed=37.2x
video:0kB audio:16kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 3.343701%

As you can see, the duration is 01.00 second. And this happens with all recorded files.

How to convert the entire file (which is 12 seconds long) to its full length?

Note: It seems that the recorded file does not have a length specified. Under Windows I renamed the file, adding an extension ".m4a" and opened the file properties:

The length attribute is empty.

Answer 1

As Gyan wrote, the conversion works with ffmpeg v4.4 which does not come with the recent Ubuntu update.

However, you can install it customly, see instructions here:

Safest way to install latest stable ffmpeg (>= 4.3) on Ubuntu 20.04 (ppa not working)?

Then the conversion from audio/mp4 (codec AAC) to mp3 works.