Converting old MPEG2 videos to HEVC - how much file space could I save?

[Gameshow Host]

I have an old drive (many terabytes) full of old PAL TV recordings, all MPEG2.

To save space, I was wondering about converting to HEVC or AVC1 (planning to batch automate with FFMPEG). I don't mind losing a little image quality if the space saving is good.

Does anyone know roughly how much space this would save, in terms of percentage of the original files?

Are there any comparison images anywhere showing this kind of conversion and how much space it saves?

[Selur]

The more noise/details your source has, the harder it is to compress without losing both details&noise.
I would recommend to reencode some clips of your source with different crf values. (crf 18-25)
This way, you should get a rough idea how much space you loose for how much detail loss.

[jagabo]

Note that HEVC doesn't really shine until you get to larger frame sizes. So it won't be as beneficial with DVD videos.

You will also have issues with interlacing. You will have to determine on a case by case basis how to encode. DVD's can be progressive, progressive with pulldown flags, progressive pulled down and encoded interlaced, or fully interlaced. Each must be handled differently.

[Gameshow Host]

Note that HEVC doesn't really shine until you get to larger frame sizes.

Oh, that's useful info, thanks! It may be that AVC gives comparable results, in which case I would choose that.

You will also have issues with interlacing. DVD's can be progressive, progressive with pulldown flags, progressive pulled down and encoded interlaced, or fully interlaced. Each must be handled differently.

Well first of all please note that there are no DVDs involved - these are all recordings from TV.

But you've raised a really good point. Many/most of the recordings are interlaced. I hadn't expected ACV1 or HEVC would have a problem with this, but I suppose they're only designed for progressive. It might be that I just ignore the interlaced videos entirely, and only convert the progressive ones.

You will have to determine on a case by case basis how to encode.

Well the scan type is listed in the recordings' info so I'm hoping there will be some way for FFMPEG to automatically detect.

Bonus question while I'm here - when I go through an interlaced recording frame-by-frame, I don't see ANY transition between shots. Between shots, the entire picture changes. How can than be if it's interlaced?

[The_Doman]

Note that HEVC doesn't really shine until you get to larger frame sizes.

But you've raised a really good point. Many/most of the recordings are interlaced. I hadn't expected ACV1 or HEVC would have a problem with this, but I suppose they're only designed for progressive. It might be that I just ignore the interlaced videos entirely, and only convert the progressive ones.

AVC and HEVC support interlaced perfectly fine, it is used here for the TV/Cable broadcasts every day.
But you need to know what you are doing when (re)encoding your video.
(AV1 is another codec, it does not support interlaced it seems)

But is it really worth it to convert all your recordings instead of leave them as is?

[El Heggunte]

Note that HEVC doesn't really shine until you get to larger frame sizes.

But you've raised a really good point. Many/most of the recordings are interlaced. I hadn't expected ACV1 or HEVC would have a problem with this, but I suppose they're only designed for progressive. It might be that I just ignore the interlaced videos entirely, and only convert the progressive ones.

AVC and HEVC support interlaced perfectly fine, it is used here for the TV/Cable broadcasts every day.

My question is,
¿are there software HEVC decoders that support interlaced video?
At least until a couple of years ago, ffmpeg for example was unable to handle interlaced HEVC correctly.

[pandy]

My question is,
¿are there software HEVC decoders that support interlaced video?
At least until a couple of years ago, ffmpeg for example was unable to handle interlaced HEVC correctly.

Nope - interlace can be supported only indirectly - you need to separate fields (simulate manually PAFF from h.264) and later guide your player to combine fields as interlace frame - this probably can be made with some pixelshader or using ffmpeg (ffplay) perhaps mpv (not sure on this) - i'm not aware of standardized way to HEVC native interlace support (to my knowledge it was designed explicitly to not support interlace directly - your encoding tool may behave cleverly and use for example Sequence Adaptive Frame Field to support interlace content but how it will be supported in player side this is big question mark).

[Sharc]

From
https://x265.readthedocs.io/en/stable/cli.html#input-output-file-options

[The_Doman]

Yes, when searching for interlaced HEVC things are much more complicated then i first thought.

So better stay with H264 when you want to use interlace.
That works fine.

[pandy]

From
https://x265.readthedocs.io/en/stable/cli.html#input-output-file-options

True but still - interlace is just separate interlace frame to fields but except this no other interlace coding tools involved so literally you can do this manually and mark field dominance and later combine with help of some tools.
If you check https://www.itu.int/rec/T-REC-H.265-202309-S/en (not the latest but freely available) then interlace source is described more thoroughly.

[cholla]

This is something I found recently by working with another video.
Try Denoising filters.
You may or may not like the results so just try this on a video or two.
Sharc came up with a good code for doing this with ffmpeg.(For my video anyway).
This reduced the size by quite a bit.

[jagabo]

If cholla is talking about this post:

https://forum.videohelp.com/threads/399508-Conversion-4-3-to-16-9/page11#post2745942

That noise reduction filter is way too strong. Especially for a non motion-compensated NR filter. All the small details are gone, there's posterization, and a lot of ghosting during motion.

[Sharc]

If cholla is talking about this post:

https://forum.videohelp.com/threads/399508-Conversion-4-3-to-16-9/page11#post2745942

That noise reduction filter is way too strong. Especially for a non motion-compensated NR filter. All the small details are gone and there is a lot of ghosting when there is motion.

Yes indeed, way too strong. I used these excessive settings of the 2 filters as an eye-catching extreme killer example for the first few grainy seconds, to experiment with, not as a recommendation.

[cholla]

If cholla is talking about this post:https://forum.videohelp.com/threads/399508-Conversion-4-3-to-16-9/page11#post2745942

Yes.
I also thought they were too strong but that was also discussed.
I tried reducing them but the more they were reduced the more the noise or graining.
I did not try but even at half I believe the file size would be a lot smaller.

Remember the OP wrote this:

I have an old drive (many terabytes) full of old PAL TV recordings, all MPEG2.
I don't mind losing a little image quality if the space saving is good.

The denoising set to less might be just what the OP is wanting.
Horse.m2ts is the rip strait from the full decrypted rip done with Passkey. Horse.m2ts 134 MB
Horse(01).m2ts has the full denoise filters. Horse(01).m2ts 30.2 MB
Horse(02).m2ts has the deoise filter values at half of Horse(01).m2ts. Horse(02).m2ts 43.7 MB
The OP can take a look & see if interested or not.

[hello_hello]

Stretching seems like an unnecessary evil when there's picture you can crop that you probably won't miss.

[jagabo]

That TemporalDegerain2 video looks much better than the hqdn3d filtered versions posted earlier. One really needs a motion compensated filter like that when applying strong noise reduction. I don't know if ffmpeg has one though.

[Sharc]

That TemporalDegerain2 video looks much better than the hqdn3d filtered versions posted earlier. One really needs a motion compensated filter like that when applying strong noise reduction. I don't know if ffmpeg has one though.

Not as I know.
https://trac.ffmpeg.org/wiki/DenoiseExamples
None of these ffmpeg denoisers are motion compensated as I understand.

[cholla]

I did not intend to hijack the OP's topic.
I wanted to let the op know that denoise would give a smaller file size.
I posted the example videos to show the op what this filter does to let the OP decide if this was acceptable for his purposes.

The hqdn3d is a bit strong but it can be set to less denoising & that might also work to make the size some smaller.
The code settings for ffmpeg hqdn3d=15.0:15.0:15.0:15.0 are too strong.
These were selected by Sharc based on Alwin's settings for avidemux filter "Mplayer Denoise 3D HQ".
I do not know if these are exactly the same filter but the results are close to the same

This is not a "motion compensated filter".
I tried vaguedenoiser with ffmpeg but it seemed to do very little even with strong settings recommended for it.
vaguedenoiser (7.6 fps) - another color neutral wavelet denoiser.
http://avisynth.nl/index.php/VagueDenoiser

I have been trying to use the avisynth's TemporalDegerain2 but so far I get errors using VDub2.
I plan to start a new thread to ask about this so I do not further hijack the OP's topic.