What command lines to use to convert from avi to mp4, but without destroying the framesize and making the file small as the original size or a little bit bigger, and same thing with mp4 to avi? Whenever I tried converting it became like 2 gb

4 Answers 4


Depending on how your original file was encoded, it may not be possible to keep the file size.

This command should keep frame sizes and rates intact while making an mp4 file:

ffmpeg -i infile.avi youroutput.mp4

And this command will give you information about your input file - the frame size, codecs used, bitrate, etc.:

ffmpeg -i infile.avi

You can also play with the acodec and vcodec options when you generate your output. Remember also that mp4 and avi files can use various codecs and your mileage may vary according to which codec you pick.

  • 8
    I think it's better to use ffprobe -i infile.avi instead of ffmpeg -i infile.avi for getting informations, as the latter results in the "At least one output file must be specified" error.
    – user22304
    Sep 23, 2012 at 10:41

As far as i understand it's required to replace avi-container with mp4 one (formally - ISO base media file format ISO/IEC 14496-12 ).

if you run the following command:

ffmpeg -i input.avi -y output.mp4

In such case ffmpeg re-encodes elementary streams within input.avi (change containers and re-encode is the default mode of ffmpeg). It's worth noticing that re-encoding might deteriorate visual and/or audio quality.

Therefore, it's recommended to disable re-encoding by "c:v copy c:a copy" codec options:

ffmpeg -i input.avi -c:v copy -c:a copy -y output.mp4

In the above case ffmpeg merely changes shells (containers)

  • When copying both audio and video you can use -c copy rather than specifying both.
    – Hipponax43
    Aug 9, 2021 at 15:57

I was very interested in converting avi files to mp4. Reading your post, I remembered this ffmpeg command:

ffmpeg -i input.avi -strict -2 output.mp4

The command -strict -2 is necessitated by the AAC codec which is experimental, but works (libaac), if you add those two parameters. The output file is high-quality by default.

  • The output quality seems to be the same as with ffmpeg -i infile.avi youroutput.mp4 as given in @rbanffy 's answer?
    – aspiring1
    Aug 13, 2020 at 10:07

I have found this one:: Libav in Linux.

Installation: run command

sudo apt-get install libav-tools

Video conversion command:

Go to folder containing the video and run in terminal

avconv -i oldvideo.mp4 -ar 22050 convertedvideo.webm
  • for windows you can use mingw32 and configure Libav as follows: ./configure --target-os=mingw32 --arch=x86 --enable-shared --enable-static --enable-dxva2 --disable-encoders --enable-hwaccel=dxva2 --extra-cflags=-O3 --enable-pthreads and then compile Libav with 'make' . Thus, you can get windows version of 'avconv' Aug 11, 2021 at 8:00
  • On MAC you can install libav by simple command: brew install libav Aug 11, 2021 at 8:05
  • Sounds Intresting @ShevachRiabtsev Aug 17, 2021 at 7:43

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