Which crf value x264

Choose a higher CRF. You should use CRF encoding primarly for offline file storage, in order to achieve the most optimal encodes. For other applications, other rate control modes are recommended. For other CRFs and resolutions, the rates vary accordingly.

You can clearly see the logarithmic relationship between CRF and bitrate. Typically you would achieve constant quality by compressing every frame of the same type the same amount, that is, throwing away the same relative amount of information.

In tech terminology, you maintain a constant QP quantization parameter. The quantization parameter defines how much information to discard from a given block of pixels a Macroblock. This typically leads to a hugely varying bitrate over the entire sequence. Constant Rate Factor is a little more sophisticated than that.

It will compress different frames by different amounts, thus varying the QP as necessary to maintain a certain level of perceived quality. It does this by taking motion into account. This will essentially change the bitrate allocation over time. For example, here is a figure from another post of mine that shows how the bitrate changes for two video clips encoded at different levels 17, 23 of constant QP or CRF:.

The line for CRF is always lower than the line for CQP; it means that the encoder can save bits, while retaining perceptual quality, whereas with CQP, you waste a little bit of space.

This effect is quite pronounced in the first video clip, for example. Because of this, a video encoder can apply more compression drop more detail when things are moving, and apply less compression retain more detail when things are still. With low motion, compression artifacts become more salient visually apparent and thus more distracting. Practically speaking, many people always use CRF for single-pass encodes and argue there is no reason to ever use CQP.

Cause how can we say that crf18 in x equals crf20 terms of image quality in x, when crf20 preset 'fast' will produce image quality vastly different to crf20 preset 'slower'?

In my experience slower presets uses higher bitrate at given crf-value than faster ones in x, and the opposite is true for x So TS question can only be answered at best at specific encoder settings. So, depending on the content, x can look better than x at the same QP. This will be somewhat content dependent. I'd think x anime using --tskip would look at lot better at the same QP than x But for noisy film grain content, the gap might be smaller or non-existent.

So, at a high level, starting with the same CRF is a decent ballpark, but I don't think we're going to have anything substantially more accurate without specifying parameters and content. I'd probably start an x encode tuning with the same CRF as x, and go from there. Or maybe start it at 2 higher if I think the CRF might have been overkill in some sequences in x Find More Posts by benwaggoner. Thread Tools. The time now is However, the risk of transient quality issues is very real with CBR.

The average and peak bitrates are inline with the football clip above, but the VMAF score is In contrast, with CRF encoding, a single-pass encoding mode, you choose a quality target and the encoder adjusts the bitrate to achieve that quality level. CRF values range from 0 to 51, with lower numbers delivering higher quality scores. CRF encoding works well for archiving or for producing mezzanine files for upload and transcoding. How do you harvest available bandwidth savings while ensuring a reasonable data rate limit?

The relevant portion of the command string would look like this. With the alternating talking head and ballet test clip, this command string produced the result shown in Figure 5. In operation, the encoder used the CRF value to encode the talking head region and applied the cap in the ballet regions. However, as you see, there is significant bitrate variability, which could hinder deliverability using constrained connections. In a high motion clip, like the football test clip, there are many regions in the clip where the CRF value produces a data rate higher than the cap.

In these regions, the cap controls the bitrate, not the CRF value. The average bitrate is about the same, though the capped CRF clip has a much lower peak.

Average VMAF scores are also very similar. Figure 6 shows the comparison Result Plot from VQMT; again, when looking at the frames at the sites of the major stalactites, I saw no observable difference. In essence, this makes capped CRF a per-title encoding technology that you can implement with almost all encoding tools, live and VOD, that are based on FFmpeg.

If transient issues are minimal and you are considering capped CRF, you should experiment with different CRF levels see here. Develops training courses for streaming media professionals; provides encoding-related testing services to encoder developers; helps video producers perfect their encoding ladders and deploy new codecs.

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