[mythtv-users] mythtranscode in V31

[David King]

On 4/5/20 10:08 PM, Stephen Worthington wrote:
> On Sun, 5 Apr 2020 15:08:12 -0400, you wrote:
>
>> I'm biased against MPG or TS files as being
>> less compact than MKV (H264) files with similar quality.
> You have the wrong idea about MPG and TS files.  They are container
> formats - what is inside them is what matters.  In New Zealand, they
> contain what is broadcast here, which is H.264, just as you are
> putting in MKV files.  Your MKV files are likely more compact for one
> or both of two reasons:
>
> 1) Your source (broadcast) recording format is not using H.264 inside,
> but something that is less efficient (MPEG2 video, for example).
>
> 2) You are telling your MKV conversion software to do lossy
> compression to a lower bit rate in H.264 than the original file.  So
> of course it will be smaller, but also lower quality, both because of
> the lower bit rate, and due to the inevitable loss of quality caused
> by any lossy conversion process.
>
> If you want the best quality in your MKV H.264 conversions then you
> should be using a profile that specifies the best H.264 format that
> your playback devices can play.  It is likely that if you are just
> using a default setting for the profile that it will be creating a
> mid-range H.264 profile like Main at L2.  If you encode in High at L4, for
> example, which MythTV can play happily, you get significantly higher
> quality for the same bit rate, or a lower bit rate for the same
> quality, or some combination of both.  High at L4 is what New Zealand TV
> broadcasts use.
>
> See here for some information about H.264 profiles and levels:
>
> https://www.rgb.com/h264-profiles
> https://en.wikipedia.org/wiki/Advanced_Video_Coding

Just like you, my starting point is MythTV recordings with h264 video
and ac3 audio in a TS (MPEG2) container.  My experience is that when I
that use Myth's tools to transcode that down to anything smaller, the
quality/file size trade-off is nowhere near as good as when I use
something like ffmpeg or HandBrake to re-encode the video into h264/ac3
in a MP4 or MKV container, regardless of which mythtranscode profile I
use.  Logically this never made sense to me as all of these tools are
based on the same set of underlying codec libraries.  But it was what it
was and I never cared enough to wade through the myriad of encoding
options to analyse the cause.  I just used the tools, and options, that
gave me the results I wanted.

I started out years ago with a script that did what John Finley
described as his workflow, to "edit" the TS recording using MythTV's
tools and set a cut list, do a lossless transcode to remove the
commercials using --cleancut and pipes as I described earlier, and then
use HandBrake to re-encode and shrink the file into a more compact
h264/aac MP4 container.  Recently I rewrote this script to eliminate the
middle step, the lossless transcode.  Now I go directly from the
original recording, transcoding it with the --cleancut option and piping
it to ffmpeg which outputs a final re-encoded, compact h264/ac3 MKV file. 

I'm not trying to convince anyone that my approach is best.  All I was
doing was letting John know about a "gotcha" that I ran into when I was
working out my process to do what he appears to be trying to do, while
trying to get precise edits in my videos.  At the time, it took me weeks
to learn about the --cleancut option, and how to use it.  I thought
maybe I could save him a little time.  I had no intention of starting up
a technical back-and-forth over which codecs and which container formats
are best.

David King
dave at daveking dot com