My input is a .mp4 video file.
Try #1
ffmpeg -i pipe:0 -y -map a media/73.mp3
Error:
ffmpeg version 3.3.3 Copyright (c) 2000-2017 the FFmpeg developers
built with Apple LLVM version 8.1.0 (clang-802.0.42)
configuration: --prefix=/usr/local/Cellar/ffmpeg/3.3.3 --enable-shared --enable-pthreads --enable-gpl --enable-version3 --enable-hardcoded-tables --enable-avresample --cc=clang --host-cflags= --host-ldflags= --enable-libmp3lame --enable-libx264 --enable-libxvid --enable-opencl --enable-videotoolbox --disable-lzma --enable-vda
libavutil 55. 58.100 / 55. 58.100
libavcodec 57. 89.100 / 57. 89.100
libavformat 57. 71.100 / 57. 71.100
libavdevice 57. 6.100 / 57. 6.100
libavfilter 6. 82.100 / 6. 82.100
libavresample 3. 5. 0 / 3. 5. 0
libswscale 4. 6.100 / 4. 6.100
libswresample 2. 7.100 / 2. 7.100
libpostproc 54. 5.100 / 54. 5.100
[mov,mp4,m4a,3gp,3g2,mj2 @ 0x7f977d800000] stream 1, offset 0xa8: partial file
[mov,mp4,m4a,3gp,3g2,mj2 @ 0x7f977d800000] Could not find codec parameters for stream 0 (Video: h264 (avc1 / 0x31637661), none(smpte170m/smpte170m/bt709), 320x176, 300 kb/s): unspecified pixel format
Consider increasing the value for the 'analyzeduration' and 'probesize' options
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'pipe:0':
Metadata:
major_brand : mp42
minor_version : 0
compatible_brands: mp42isomavc1
creation_time : 2012-03-13T08:58:06.000000Z
encoder : HandBrake 0.9.6 2012022800
Duration: 00:00:10.03, bitrate: N/A
Stream #0:0(und): Video: h264 (avc1 / 0x31637661), none(smpte170m/smpte170m/bt709), 320x176, 300 kb/s, 25 fps, 25 tbr, 90k tbn, 180k tbc (default)
Metadata:
creation_time : 2012-03-13T08:58:06.000000Z
encoder : JVT/AVC Coding
Stream #0:1(und): Audio: aac (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 160 kb/s (default)
Metadata:
creation_time : 2012-03-13T08:58:06.000000Z
Stream #0:2(und): Audio: aac (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 160 kb/s
Metadata:
creation_time : 2012-03-13T08:58:06.000000Z
Stream #0:3(und): Subtitle: mov_text (text / 0x74786574), 0 kb/s
Metadata:
creation_time : 2012-03-13T08:58:06.000000Z
Stream mapping:
Stream #0:1 -> #0:0 (aac (native) -> mp3 (libmp3lame))
Stream #0:2 -> #0:1 (aac (native) -> mp3 (libmp3lame))
[mov,mp4,m4a,3gp,3g2,mj2 @ 0x7f977d800000] stream 1, offset 0xa8: partial file
pipe:0: Invalid data found when processing input
Finishing stream 0:0 without any data written to it.
Finishing stream 0:1 without any data written to it.
[mp3 @ 0x7f977b846800] Invalid audio stream. Exactly one MP3 audio stream is required.
Could not write header for output file #0 (incorrect codec parameters ?): Invalid argument
Error initializing output stream 0:1 --
Conversion failed!
Try #2
ffmpeg -i pipe:0 -y -vn -acodec copy media/72.mp3
Error:
[...]
[mp3 @ 0x7febed835200] Invalid audio stream. Exactly one MP3 audio stream is required.
Could not write header for output file #0 (incorrect codec parameters ?): Invalid argument
Try #3
ffmpeg -i pipe:0 -y -codec:a libmp3lame -qscale:a 2 media/74.mp3
No error with ffmpeg, but the file is invalid (it's size is 334 bytes)
Try #4
ffmpeg -i pipe:0 -y -vn -acodec mp3 media/78.mp3
No error with ffmpeg, but the file is invalid (it's size is 334 bytes)
Try #5
ffmpeg -f mp4 -i pipe:0 -y media/80.mp3
No error with ffmpeg, but the file is invalid (it's size is 334 bytes)
What am I doing wrong? This seems like a fairly easy thing to do...
FFmpeg can't update metadata in WAVE files when output is written over a non-seekable protocol like a pipe. Quicktime seems to rely on metadata to determine file validity. You have to write to file or some other seekable protocol.
Please refer to this question.