Details on encoder settings (Accelerated GStreamer)

Robotics & Edge Computing Jetson & Embedded Systems Jetson TX2
1

Hello everybody,

I was wondering about the range of the parameters of the accelerated encoders supported in GStreamer (nvv4l2 & omx). For example, the iframeinterval parameter has a range of 0 to 4294967295.

How is this range mapped on the actual I-frame interval?
How is it with the other encoder parameters?

Thanks in advance and best regards,
Bruno

3

Hi,
Theoretically iframeinterval can be set to very large value, but generally we set it to 1-2 second interval so that you can seek in the stream more easily. Since decoding starts from I frames.

For 30fps, we suggest set to 30 or 60.

4

Hi DaneLLL,

thank you for your answer!

So, the actual I frame interval is iframeinterval/framerate?

What about the other numeric parameters?

  • quant-i/p/b-frames
  • SliceIntraRefreshInterval
  • slice-header-spacing

Is there a general mapping/scaling process of the 32bit/64bit parameters?
The quantization parameters (quant-i/p/b-frames) of the nvv4l2h264enc have a default value of 2^32 - 1. If that is the true value of the quantization parameter (no mapping/scaling) I have a wrong understanding of the quantization process.

Best regards
Bruno

5

Hi,

  • quant-i/p/b-frames
    qp range is 0 - 51. Please set in this range.

  • SliceIntraRefreshInterval
    iframeinterval is to set interval of IDR frames, and SliceIntraRefreshInterval is to set interval of I frames. generally we set IDR frame interval > I frame inteval. Such as iframeinterval=30 SliceIntraRefreshInterval=15

  • slice-header-spacing
    This is to set how many macroblocks are put in one encoded slice. There is same properties in jetson_multimedia_api sample and please refer to
    How does slice mode video encoding work for Jetson? - #14 by DaneLLL
    So the range depends on the resolution.

6

Hi DaneLLL,

thank you very much. This helped a lot!

It would be helpful to put this information in the documentation (gst-inspect-1.0 or Nvidia online documentation on Accelerated GStreamer)

Best regards
Bruno

7

Hi,
Thanks for the suggestion. We will try to improve the document. If you have further questions about setting properties, please feel free to make a post.

8

Hi DaneLLL,

I have some additional questions:

  1. Assuming I set quant-i/p/b-frames to a value higher than 51, e.g. 255, what is the resulting value? Is it capped at 51 and higher values are set to 51?
  2. The terms are a bit confusing for me, so I would be happy if you could clarify the following questions:
    The i-frames are keyframes, i.e., full frames and may come as IDR frame or non-IDR frame?
    The p-frames and b-frames are intra-frames, i.e., no full frames and are “predictions” which reference to the previous frames?
  3. Do the SliceIntraRefreshInterval and iframeinterval have a significant impact on video quality?
    Background to this question: The IDR frames are keyframes, i.e., full frames. The smaller the interval the higher the number of full frames in the encoded video, hence more detail / higher video quality. Thats how I thought it would work, but not how the encoder actually performs the compression. Where am I wrong and what did I miss respectively?

Best regards
Bruno

9

Hi,

If you set qp value > 51, it is capped at 51.

Intra frames are also I frames, please check difference of IDR and I frames:
https://topic.alibabacloud.com/a/the-difference-between-the-i-frame-and-idr-frame-in-h264_8_8_10244757.html

Yes, it has impact to video quality. Since IDR/I frames have larger size, if setting the interval to small size, more bits are distributed in IDR/I frames. We would suggest set interval to ~ 1 second. For 30 fps, suggest set interval = 30.

11

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