<p>In strict mathematical terms, no.</p>

<p>In terms of maintaining an acceptable image quality, yes. If you use CRF <code>18</code> and a preset like <code>ultrafast</code> now, you should be able to get a smaller acceptable file with preset <code>veryslow</code> later on.</p>

CC BY-SA 3.0
2015-12-11T08:16:17.283Z
Ahh too bad. Upon testing a longer clip, the size reduction is around 20%. I can live with that I guess. Thanks for the quick answer!
Yifeng Mu
CC BY-SA 3.0
2015-12-11T06:24:57.807Z
2015-12-11T06:24:57.807Z
Gyan
<p>My situation:</p>

<ol>
<li>Transcoding 1080p bluray videos to HEVC. Audio untouched;</li>
<li>My rig is old (pre-2012) and to speed up the process I'm using <code>--preset ultrafast</code>;</li>
<li>From x265 documentation, I understand that video quality is independent of the preset used. And the slower the preset, the better the compression ratio it seems;</li>
<li>I'm using FFmpeg.</li>
</ol>

<p>My Reasoning:</p>

<ol>
<li>I want to start converting to HEVC now because the codec is good enough for me and the space saving is phenomenal;</li>
<li>I've seen people reporting a 35GB video compressed to 1GB or so with <code>crf=18</code> and <code>--preset veryslow</code>. It sounds ludicrous but an experiment of my own shows about 40% additional space saving between presets <code>ultrafast</code> and <code>veryslow</code>.</li>
</ol>

<p>The Question:</p>

<p>When I get a new rig with a more capable CPU (Skylake or later, I hear), is it possible for me, to "re-compress" my HEVC videos using eg. <code>--preset veryslow</code>, without quality loss due to encoding a second time?</p>

<ffmpeg><encoding><compression><h.265><lossless>
x265: Is it possible to re-compress HEVC video without quality loss?
Yifeng Mu
# x265: Is it possible to re-compress HEVC video without quality loss?

(Asked by: username_0 on 2015-12-11)

My situation:

1. Transcoding 1080p bluray videos to HEVC. Audio untouched;
2. My rig is old (pre-2012) and to speed up the process I'm using `--preset ultrafast`;
3. From x265 documentation, I understand that video quality is independent of the preset used. And the slower the preset, the better the compression ratio it seems;
4. I'm using FFmpeg.

My Reasoning:

1. I want to start converting to HEVC now because the codec is good enough for me and the space saving is phenomenal;
2. I've seen people reporting a 35GB video compressed to 1GB or so with `crf=18` and `--preset veryslow`. It sounds ludicrous but an experiment of my own shows about 40% additional space saving between presets `ultrafast` and `veryslow`.

The Question:

When I get a new rig with a more capable CPU (Skylake or later, I hear), is it possible for me, to "re-compress" my HEVC videos using eg. `--preset veryslow`, without quality loss due to encoding a second time?

**Tags:** ffmpeg, encoding, compression, h.265, lossless


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## 1 answers

### Answer by username_1 on 2015-12-11. Score: 3 | Accepted answer

In strict mathematical terms, no.

In terms of maintaining an acceptable image quality, yes. If you use CRF `18` and a preset like `ultrafast` now, you should be able to get a smaller acceptable file with preset `veryslow` later on.

> **Comments:**
> **username_0**: Ahh too bad. Upon testing a longer clip, the size reduction is around 20%. I can live with that I guess. Thanks for the quick answer!  

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