Lossless convert 3gp video to mp4 using ffmpeg

Question

I'm trying to get lossless conversion of 3gp to mp4 using ffmpeg.

I tried

ffmpeg -i input.3gp -vcodec h264 -c:a aac output.mp4

I tried with "libx264" for the video codec, I tried just a simple

ffmpeg -i input.3gp output.mp4

No matter what I try, for a 10 MB 3gp video I am getting a 5 MB mp4 video that doesn't seem to have the same quality.

Any suggestions are welcome.

Thank you.

EDIT

Here's what I get if I try to copy the Video and Audio codecs:

ffmpeg -i  VIDEO0004.3gp  -c:v copy -c:a copy VIDEO0004.mp4
ffmpeg version 4.4 Copyright (c) 2000-2021 the FFmpeg developers
  built with Apple clang version 12.0.0 (clang-1200.0.32.29)
  configuration: --prefix=/usr/local/Cellar/ffmpeg/4.4 --enable-shared --enable-pthreads --enable-version3 --enable-avresample --cc=clang --host-cflags= --host-ldflags= --enable-ffplay --enable-gnutls --enable-gpl --enable-libaom --enable-libbluray --enable-libdav1d --enable-libmp3lame --enable-libopus --enable-librav1e --enable-librubberband --enable-libsnappy --enable-libsrt --enable-libtesseract --enable-libtheora --enable-libvidstab --enable-libvorbis --enable-libvpx --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxml2 --enable-libxvid --enable-lzma --enable-libfontconfig --enable-libfreetype --enable-frei0r --enable-libass --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-libspeex --enable-libsoxr --enable-libzmq --enable-libzimg --disable-libjack --disable-indev=jack --enable-videotoolbox
  libavutil      56. 70.100 / 56. 70.100
  libavcodec     58.134.100 / 58.134.100
  libavformat    58. 76.100 / 58. 76.100
  libavdevice    58. 13.100 / 58. 13.100
  libavfilter     7.110.100 /  7.110.100
  libavresample   4.  0.  0 /  4.  0.  0
  libswscale      5.  9.100 /  5.  9.100
  libswresample   3.  9.100 /  3.  9.100
  libpostproc    55.  9.100 / 55.  9.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'VIDEO0004.3gp':
  Metadata:
    major_brand     : 3gp4
    minor_version   : 768
    compatible_brands: 3gp4mp413gp6
    creation_time   : 2011-02-06T16:39:49.000000Z
    copyright       : 
    copyright-eng   : 
    rating          : 0
    location-eng    : +00.0000+000.0000/??
    location        : +00.0000+000.0000/??
  Duration: 00:01:00.20, start: 0.000000, bitrate: 1369 kb/s
  Stream #0:0(eng): Video: mpeg4 (Simple Profile) (mp4v / 0x7634706D), yuv420p, 640x480 [SAR 1:1 DAR 4:3], 1355 kb/s, 9.90 fps, 9.92 tbr, 1k tbn, 60 tbc (default)
    Metadata:
      creation_time   : 2011-02-06T16:39:49.000000Z
      handler_name    : VideoHandler
      vendor_id       : [0][0][0][0]
  Stream #0:1(eng): Audio: amr_nb (samr / 0x726D6173), 8000 Hz, mono, flt, 12 kb/s (default)
    Metadata:
      creation_time   : 2011-02-06T16:39:49.000000Z
      handler_name    : SoundHandler
      vendor_id       : [0][0][0][0]
[mp4 @ 0x7fbaf5009600] Could not find tag for codec amr_nb in stream #1, codec not currently supported in container
Could not write header for output file #0 (incorrect codec parameters ?): Invalid argument
Error initializing output stream 0:1 -- 

Answer 1

If the codecs of your input file are already h264 and aac for video and audio, respectively, you can just copy without decoding and encoding again.

ffmpeg -i input.3gp -c:v copy -c:a copy output.mp4

The options -c:v copy and -c:a copy indicate video and audio won't be encoded again, respectively. If audio format in the input cannot be embedded to the output, you need to omit -c:a copy from above command.

If you need to encode again, an option -qscale 0 will result similar quality (but not lossless). below is an example. You might combine with -c:v copy or -c:a copy if you don't need to encode video or audio again.

ffmpeg -i input.3gp -qscale 0 output.mp4