Recordings get LARGER after removing commercials!

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aazman
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Recordings get LARGER after removing commercials!

Post by aazman » Fri Dec 29, 2017 3:12 am

After a new recording, I manually generate a cut list from the automatically detected commercials (they aren't always accurate, especially at the end of a show, so I manually check and fix them).

Then I go back to the Watch Recordings menu, and select Job Options:Begin Transcoding:Autodetect. It successfully cuts out the commercials, but then the file size gets LARGER. I watched a recording go from 0.57GB to 0.76GB. Also, 3GB seems large for a 30 min show (with commercials still), and 10GB for a 1 hr show (After removing commercials)

Why is this happening? What setting do I need to change to get the file size to actually get, you know, smaller after removing 1/3 of the recording?

Mythbuntu 16.04
Mythtv 0.28.1+fixes

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pgbennett
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Re: Recordings get LARGER after removing commercials!

Post by pgbennett » Fri Dec 29, 2017 3:41 pm

You can do a "lossless transcode" which removes the cut sections but does not re-encode anything. Here is an example.

Code: Select all

mythtranscode -i /storage/2704_20171107005515.ts -m --honorcutlist  --passthrough  -o ~/tmp/transcode.ts
You will have to substitute the correct path and file name. After completing the transcode you can overwrite the original file with the transcoded file (I would keep the original around for a while in case of problems). If you overwite the original file with the new one you need to rebuild the seektable.
You can get a list of transcode options using

Code: Select all

mythtranscode --help
But I have found that many of the options do not work. The above example does work

aazman
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Re: Recordings get LARGER after removing commercials!

Post by aazman » Sat Dec 30, 2017 3:14 am

Thanks for the quick reply.

Is there a way to do all that from within the Frontend, while I'm generating the cut list? I can go back to the terminal every time, but that - coupled with finding the non-obvious name for each recording - seems excessive.

I used to do this all the time before upgrading, all within the frontend, and I don't ever remember the files getting bigger. What if I select low, instead of autodetect, when starting the transcoding?

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pgbennett
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Re: Recordings get LARGER after removing commercials!

Post by pgbennett » Sat Dec 30, 2017 5:58 pm

One way would be to set up a user job. Set it up in mythtv-setup->general->JobQueue (job commands). It can automatically insert the file name in the command using %FILE% . See https://www.mythtv.org/wiki/User_Jobs for a list of parameters you can use. You can rename the job with a name that makes sense, instead of "User job 1". Then you can start it from the frontend in the same way you could start a transcode.

aazman
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Re: Recordings get LARGER after removing commercials!

Post by aazman » Sat Dec 30, 2017 8:29 pm

Thanks, that's helpful.

Any thoughts on why the file gets bigger, not smaller? I can just correct the inaccurate commercial cuts and keep the original file without transcoding to keep file size down.

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pgbennett
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Re: Recordings get LARGER after removing commercials!

Post by pgbennett » Sat Dec 30, 2017 8:52 pm

I ran some tests and the default transcode was converting the file to RTJPEG format, which is inferior to almost any other format. The file landed up being about 2.5 times as large as before. You can select MPEG4 format, but the still is inefficient and results in a larger file. I think few people are using transcode and it has lagged behind advances in video technology. I think many people who want to reduce the file size are using tools like HandBrake.

aazman
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Re: Recordings get LARGER after removing commercials!

Post by aazman » Sat Dec 30, 2017 9:14 pm

Hmm... Seems odd.

And you suggest this lossless transcoding as a way to cut the commercials, but not convert the file to an inferior file type? The lossless transcoding should keep it the same file type, thus actually shrink the file size?

I don't know anything about HandBrake, would it help my situation? I got a 1.5TB drive so that I could archive series of shows I watch a lot.

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