[FFmpeg-user] Fwd: compression bit rates in todays world

[Bhikkhu Mettavihari]

Greetings Steve

Thank you for your recommendation
I shall try them out.
There is so much to learn about ffmpeg.

I fully understand why sometimes one like to keep the original footage.
In my case the majority of the content only has a value for 5 years.
We are doing educational programs which will be renewed every 5 years
due to syllabus change

Please allow me to ask you another question.
For the production of my Television Quality we have been given the below specs

Container
v1.0 MP4 (MPEG-4 Part 14 ), MXF, QuickTime (.mov)

Video
Resolution 720 x 576
Frame rate 25 fps
Codec  ITU-T H.264 (ISO/IEC 14496-10 – MPEG-4 Part 10)
Bit rate > 3.5 Mbps Variable Bit Rate

Audio
Resolution 16 bit
Sample rate 48 kHz
Channels 2.0 (adjust if required with mulch-lingual option)
Codec HE-AAC
Bit rate 128 kbps

Multilingual audio containment Options
Option 1 As multi-track, each compressed with audio codec and
contained as separate streams
Option 2 As multi-channel, compressed with audio codec and contained
as single stream. In this case Audio channels value is 4.0 for two
stereo languages and bit rate to be adjust accordingly. Care must be
taken to maintain consistent channel mapping throughout.

What would you recommend me as a compression formula for this spec.

with metta
Mettavihari


On Wed, Sep 3, 2014 at 8:20 PM, Steve Boyer <steveboyer85 at gmail.com> wrote:
> 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:
> https://trac.ffmpeg.org/wiki/Encode/H.264#CBRConstantBitRate).
>
> 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
> path:
>
> 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?
>
> Steve
>
> On Wed, Sep 3, 2014 at 5:08 AM, Bhikkhu Mettavihari <tv.lists at gmail.com> wrote:
>>
>> Greetings,
>>
>> 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.
>> 3500K
>> 1024k
>> 512k
>> 268k
>> 130k
>> 038k
>>
>> with metta
>> Mettavihari
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