Converting FLV to MP4 Using FFMPEG and Preserving the Quality
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 aac -b:a 160k output.mp4
If you want to change only the audio or only the video codec, you can use -c:a copy
or -c:v copy
to copy the one you want to keep.
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 inprove the audio quality, choose a higher bitrate (160k in the example above).
With both the audio and video quality, your results will vary depending on the quality of the source.
more info on FFMPEG aac encoding (I've been referring to the "native" encoder described on the ffmpeg site).
Regarding the ffmpeg command suggested in the question...
-ar
refers to the audio sample rate. I recommend not messing with this parameter at all. If you want to play with audio encoding, adjust the bitrate (-b:a 160k
above) and let the encoder choose what to do based on that.
For reference, here's what it means.
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 are downconverting CD material this is a good choice. If you're starting with 48KHz source i'd use 24Khz instead.
You should get info on the sample rates from the ffmpeg -i
command I suggested at the top.
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Updated on September 17, 2022Comments
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Admin almost 2 years
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.
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Dan Pritts over 12 yearsre-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.
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aresnick almost 5 yearsRegarding the command forcing audio/video codecs: As of September 2019, I found that
ffmpeg
discontinued support forlibaac
. This question suggests either usingffmpeg
's native AAC encoder via-c:a aac
or the Fraunhofer FDK AAC codec via-c:a libfdk_aac
(which require compilingffmpeg
with support forlibfdk_aac
). -
Dan Pritts over 4 yearsUpdated the answer to use the native aac encoder.