Converting a .flv file to .mp4 format through ffmpeg results in error

Question

I currently use ffmpeg version 3.2.2, and the issue I run into is that when I try to convert a sample .flv file, it does not convert it properly to a the expected .mp4 format. The error I come across:

ffmpeg -i flv.flv -vcodec copy -acodec copy flv.mp4
ffmpeg version 3.2.2 Copyright (c) 2000-2016 the FFmpeg developers
  built with Apple LLVM version 8.0.0 (clang-800.0.42.1)
  configuration: --prefix=/usr/local/Cellar/ffmpeg/3.2.2 --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 --disable-lzma --enable-vda
  libavutil      55. 34.100 / 55. 34.100
  libavcodec     57. 64.101 / 57. 64.101
  libavformat    57. 56.100 / 57. 56.100
  libavdevice    57.  1.100 / 57.  1.100
  libavfilter     6. 65.100 /  6. 65.100
  libavresample   3.  1.  0 /  3.  1.  0
  libswscale      4.  2.100 /  4.  2.100
  libswresample   2.  3.100 /  2.  3.100
  libpostproc    54.  1.100 / 54.  1.100
[flv @ 0x7f9af4800000] audio stream discovered after head already parsed
[flv @ 0x7f9af4800000] video stream discovered after head already parsed
Input #0, flv, from 'flv.flv':
  Metadata:
    encoder         : Lavf53.24.2
  Duration: 00:00:26.40, start: 0.000000, bitrate: 1589 kb/s
    Stream #0:0: Audio: aac (LC), 48000 Hz, 5.1, fltp
    Stream #0:1: Video: flv1, yuv420p, 1280x720, 25 fps, 25 tbr, 1k tbn
File 'flv.mp4' already exists. Overwrite ? [y/N] y
[mp4 @ 0x7f9af5829e00] Could not find tag for codec flv1 in stream #0, codec not currently supported in container
Could not write header for output file #0 (incorrect codec parameters ?): Invalid argumentStream mapping:
  Stream #0:1 -> #0:0 (copy)
  Stream #0:0 -> #0:1 (copy)
    Last message repeated 1 times

I tried using some online converters to see if they have issues converting the file, but all of them converted it properly to mp4.

I would appreciate any help on this!

Solution

As mentioned in the comments, ffmpeg does not mux flv1 video streams in MP4.

Re-encode instead:

ffmpeg -i flv.flv -vcodec libx264 -acodec copy flv.mp4

Comments

[Ipor Sircer]

This message is very clear: "codec not currently supported in container". I think online converters also reencode the video to be fit in mp4.

[Elisa Cha Cha]

@IporSircer You could make that the answer. "flv1" / Sorenson Spark / Sorenson H.263 (Flash Video) isn't supported in MP4 container and the online converters re-encode instead of re-mux.

[Chris Palmer Breuer]

Thanks for your comments. I'm very new to this topic, so any advice helps. It might seem obvious to some, but for me, I don't think I fully even understand what a "codec" is. I am just working on a project that allows user to upload video, but I am trying to have the video be able to be streamed, so some formats I think I will have to convert.

[Elisa Cha Cha]

@IporSircer Nevermind. You were beaten to it. Got to be quick.