[Question]: Macroblock Skip Threshold

[BlueWaterCrystal]

Hi,

How do you increase the macroblock skip threshold to use more skip MB?

I've tried increasing the values in SkipVal_P_Common but nothing seems to change

[Xiaogangli-intel]

Hi @BlueWaterCrystal, which platform are you working on? And are you using low-power profile?

[BlueWaterCrystal]

Hi @BlueWaterCrystal, which platform are you working on? And are you using low-power profile?

Hi

I'm working on:
OS: Linux Debian 11
Gstreamer: 1.18
CPU: i5-6200U Skylake

The profile is set to none.

[OttoYang]

@DenWolf Hi Denis, could you please take a look at this question?

[DenWolf]

Hi @BlueWaterCrystal ,
I understand that you asked this question long time ago, but I hope that maybe it's still actual for you and may be helpful for others, so lets try to resolve this topic.

In general, Skip MB thresholds in encoding controls by increasing Quantization ratio -> frames (and part of the frames) become more similar with each other -> this similarity (low delta diff) increase the probability of Skipping MBs

I suppose it's better to start from Driver API usage (or higher-level applications) to control MB skipping level and using embedded algorithms (of course with related Quality degradation):

• use higher QP values in CQP mode - up to maximum 51 (I suppose it's good to start from QP=37 and increase it based on experiments)
• use a low Bitrate values in BRC modes

If you have some information about the video stream content like which frames do you want to "skip" or about the data on a part of the frame (for example, during video conference or streaming) - you can use our special media features for such scenarios:

• ROI (Region Of Interests) - set the lower/higher quality on some rectangle areas - more information about that on MediaSDK manual - https://github.com/Intel-Media-SDK/MediaSDK/blob/master/doc/mediasdk-man.md#mfxextencoderroi
• MBQP - the similar feature as ROI but here you need to fulfil QP mask for the full frame - https://github.com/Intel-Media-SDK/MediaSDK/blob/master/doc/mediasdk-man.md#mfxextmbqp
• use https://github.com/Intel-Media-SDK/MediaSDK/blob/master/doc/mediasdk-man.md#mfxskipmode or https://github.com/Intel-Media-SDK/MediaSDK/blob/master/doc/mediasdk-man.md#mfxextmbdisableskipmap

[DenWolf]

About the primary question related to SkipVal_P_Common:
As you can see in Driver source code - it's a 3-dimentions-array with a thresholds based on frame/slice QP (as I mentioned in my previous comment) and transform_8x8 -

media-driver/media_driver/agnostic/gen9_skl/codec/hal/codechal_encode_avc_g9_skl.cpp

Line 2191 in 55c4003

Cmd.common.DW32.SkipVal = SkipVal_P_Common

Effect of changing this matrix could be different and related to multiple other factors/metrics/thresholds in AVC encoding algorithm - except the mention QP per frame, it could be affected by Costs of prediction or partition for different modes for example, and so on so forth -> so, result is some kind of unpredictable here.

@BlueWaterCrystal - feel free to ask any questions you have.

Best regards,
Denis

[BlueWaterCrystal]

Hi, Thank you for getting back to me.

I believe we came to the same conclusion.

Is MBQP part of FEI?
Additionally, it looks like FEI may be suitable for this solution, though last time I tested the samples I wasn't able to figure out what was needed for it to work.

https://github.com/Intel-Media-SDK/MediaSDK/blob/master/doc/mediasdkfei-man.md

The end goal is if the frame is too big, skip more macroblocks instead of the whole frame.

[DenWolf]

Hi @BlueWaterCrystal ,
Great that it still could be helpful for you!

>> The end goal is if the frame is too big, skip more macroblocks instead of the whole frame.
OK, as I right understand, your primary purpose is somehow decrease the frame size in case of it's too big.

For this purpose I see the next solutions:

• using feature MaxFrameSize - https://github.com/Intel-Media-SDK/MediaSDK/blob/master/doc/mediasdk-man.md#mfxextcodingoption3 - you can set in MaxFrameSizeI and/or MaxFrameSizeP to limit frame size in bytes specifically for I-frames and P-/B-frames
• if you using VBR rate control, you can also try to use LowDelayBRC=ON - https://github.com/Intel-Media-SDK/MediaSDK/blob/master/doc/mediasdk-man.md#mfxextcodingoption3 - this mode encode frames in "more similar" filesize without significant size-drop or increasing
• if you are using CBR or VBR - I suppose you can try to use a different HRD buffer settings
• for experiment purpose you can also try to use ExtBRC=ON

Some questions from my side:

• which rate control are you using - CBR / VBR / ICQ / CQP / ... ?
• are you using encoder via MediaSDK or via VAAPI directly?
• if possible, maybe you could share the command-line which you are using and input stream as example?

Best regards,
Denis