24

Im trying to use ffmpeg to convert my flv files to mp4 to play them on iOS devices but the converted video has a much worse quality than the original one.

Here is the command i use:

ffmpeg -i input.flv -ar 22050 output.mp4

I would really appreciate if someone could provide me with the best settings for flv to mp4 conversion.

migrated from stackoverflow.com Oct 4 '12 at 20:53

This question came from our site for professional and enthusiast programmers.

40

Depending on the codecs used in your FLV you may be able to get away with simply re-wrapping it in an mp4 container. You'll need H.264 or MPEG4 simple profile video and AAC audio. You can find out some info on your source file with ffmpeg -i input.flv

I'm not sure whether simply having H.264/MPEG4 Simple + AAC is good enough or if there are specific options to the codecs that are supported. It's easy enough to test:

Try using

ffmpeg -i input.flv -c copy -copyts output.mp4

-copyts is copy timestamps it will help audio sync.

If that doesn't work, try forcing audio and video codecs. This will re-encode the file:

ffmpeg -i input.flv -c:v libx264 -crf 23 -c:a libfaac -q:a 100 output.mp4

To improve the video quality, you can use a lower CRF value, e.g. anything down to 18. To get a smaller file, use a higher CRF, but note that this will degrade quality.

To improve the audio quality, use a higher quality value. For FAAC, 100 is default.


Here are a couple thoughts on the ffmpeg command suggested in the question.

-ar refers to the audio sample rate. I would recommend not messing with this until you understand things better. If you want to play with audio encoding, adjust the bitrate (e.g., -b:a 128k) and let the encoder choose what to do based on that.

If you do end up going down this road...

CD quality is 44100Hz sampling; typical video uses 48000Hz.

You may note that 22050 in the original question's example is 1/2 the cd quality sample rate. if you're downconverting CD material this is a good choice. If you're starting with 48KHz source (which you probably are; again, this is much more common than 44100 in video files) i'd use 24Khz instead. It probably won't matter much, but it may sound a little better and use a little less CPU to do the conversion.

  • re-reading my answer... In addition to the command line I gave above, you could copy only video or only audio, and re-encode the other. for example... "ffmpeg -i input.foo -vcodec copy -acodec libfaac -ab 128k -copyts output.mp4" this will copy the video stream and re-encode the audio into AAC. libfaac doesn't have great quality but it works. – Dan Pritts Mar 7 '12 at 22:15

protected by Community Sep 29 '16 at 5:00

Thank you for your interest in this question. Because it has attracted low-quality or spam answers that had to be removed, posting an answer now requires 10 reputation on this site (the association bonus does not count).

Would you like to answer one of these unanswered questions instead?