[mythtv-users] Suggested bitrate for transcoding HD Mpeg 2 to Mpeg 4

[belcampo]

On 05/29/11 23:54, Ian Evans wrote:
> On Mon, May 30, 2011 at 5:41 AM, belcampo<belcampo at zonnet.nl>  wrote:
>> I would suggest to take some 1 minute test-runs with quality settings
>> between 16 - 25 and see where YOUR sweet-spot of quality vs space vs
>> encoding-time and file-size lies.
>> After 10 runs, which will take less then 30 minutes, you'll be able to
>> make a meaningfull decision.
>
> Where do I change this? Do I leave the bitrate alone?
>
> The Autodetect from Mpeg2 transcoder is currently:
>
> Bitrate: 3500
> Max: 2
> Min: 15
>
> So do I leave the bitrate at 3500 and adjust the Min between 16-25?
I suggest to use ffmpeg, which supports the x264 codec, one of the 
options of the x264 codec is the cqp flag, for constant quality 
parameter, ffmpeg -i source -acodec copy -vcodec libx264 several other 
options -cqp 16 -f encoded-source-cqp16.ts
ffmpeg -i source -acodec copy -vcodec libx264 several other options -cqp 
17 -f encoded-source-cqp17.ts
etc.
I use for several reasons an old ffmpeg version, my encode options are:
ffmpeg -i source.ts -acodec libfaac -ab 128k -ar 48000 -ac 2 -vcodec 
libx264 -threads 2 -flags +loop -coder 1 -refs 2 -deblockalpha 0 
-deblockbeta 0  -partitions +parti4x4+partp8x8+parti8x8+partb8x8 
-me_method umh -subq 4 -me_range 16 -flags2 +dct8x8+mixed_refs -cmp 
+chroma -bf 0 -b_strategy 1 -g 75 -keyint_min 25 -sc_threshold 40 -cqp 
24 -f mpegts source-cqp24.ts
Others/Most will tell that cqp is a stupid option and that you should 
use the crf option, so -crf 24 instead of -cqp 24 as in my example.
Test it for yourself, messure and draw your own conclusions.
Multi-pass is a waste of time unless you absolutely need the max quality 
at a given size, size of a cd or dvd, otherwise if you don't need the 
past % in size, forget about multi-pass. Try yourself, see and measure 
and decide yourself.
As you see, there is no bitrate given for the video part, the bitrate is 
a result of your quality settings.
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