[FFmpeg-user] Fwd: compression bit rates in todays world
steveboyer85 at gmail.com
Wed Sep 3 16:50:42 CEST 2014
Hello, Bhikku. I'm still relatively new to these mailing lists, but I
think I can help you out some.
My main observation is that you are doing 2-pass encoding using x264
for video compression. x264 has another variable bitrate mode called
Constant Rate Factor. With this, you do not determine what your
bitrate and therefore filesize is, but you determine overall quality.
This means that videos with more motion will have much different
compression than videos with mostly still motion. This is a variable
bitrate mode but runs in a single pass. You can specify your max
bitrates if you'd like, although a smaller sized video will
automatically have a much lower bitrate at the same CRF. (more info:
Guessing a bit from your intended constant bitrates you mentioned
before, here are some ideas on the CRF that'll get you started on this
TV broadcast: crf 16
ffmpeg -i $file1.$ext -c:a libfaac -ab 128k -ac 2 -c:v libx264
-preset fast -crf 16 $file1.temp2.mp4
good internet: crf 20
normal quality: crf 22
low bandwidth: crf 26
tablet: crf 26
phone viewing: crf 30 (assuming these phones can playback MP4 files)
That being said, if you'd prefer the control over bitrates, by all
means use 2-pass encoding. In that case, I'd omit the "minrate" and
"maxrate" options; you are specifying the average bitrate already so
why constrain it to go within bitrates when you are doing a 2-pass
encode on it in order to get the best quality per MB?
Another observation is for your tablet and phone sections, your
intended video bitrate is either comparable or lower than your audio
bitrate: the audio bitrate of your "broadcast" and your "mobile phone"
version are the same. The frequency rate is different, but the file
size of the audio is the same. If you'd like to make it even smaller,
you could get by with an audio bitrate of 64k or even less (based on
how much you want to compress your video).
One final observation: I personally would prefer keeping an original
video for future editing if needed rather than a slightly transcoded
version. I'm nit-pickey that way though. Why edit anything other than
the best quality version you have access to, including the original
format which you already have?
On Wed, Sep 3, 2014 at 5:08 AM, Bhikkhu Mettavihari <tv.lists at gmail.com> wrote:
> We are compressing using ffmpeg and the following is our scripts
> I would like to have your recommendations on this.
> Technically it works OK, but your suggestions are very welcome.
> My interest is to have your input on compression standards since the
> world is changing so fast.
> In short we have these suggestions
> Mpeg2 for backup.
> with metta
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