VPU decoder would cache several frames before display the first beginning frame?

[kame_lqm]

When I tried to decode real time H264 stream over VPU decoder, I received following log:

[INFO]  Display fps will be 30

[INFO]  vpu needs more bitstream in rollback mode frame_id = 0

[INFO]  Num of Error Mbs : 4656, in Frame : 0  

VPU doesn't have picture to be displayed.toutinfo.indexFrameDisplay = -3, -1

[INFO]  Num of Error Mbs : 4656, in Frame : 0  

VPU doesn't have picture to be displayed.toutinfo.indexFrameDisplay = -3, -3

VPU doesn't have picture to be displayed.toutinfo.indexFrameDisplay = -3, -3

VPU doesn't have picture to be displayed.toutinfo.indexFrameDisplay = -3, -3      

It seems that VPU decoder will cache several frames before display the first beginning frame. Why? And how can I do to display the frame in real time without any delay? Thanks a lot.

[igorpadykov]

Hi li

one can look at below explanations and solutions for vpu latency

VPU Latency on i.MX6 

imx53 latency with h264 and udpsrc 

https://community.nxp.com/thread/308415 

Best regards
igor
-----------------------------------------------------------------------------------------------------------------------
Note: If this post answers your question, please click the Correct Answer button. Thank you!
-----------------------------------------------------------------------------------------------------------------------

[kame_lqm]

Hi igorpadykov,

Thanks for your nice reply. I can not find the solution in those explanations. I try to describe the detail of my question as bellow.

I transmit the H264 stream (1080p@25fps) over cable network (UDP Socket) to the imx6dl demo board (linux version),  the demo board receives the stream, and tries to decode it by VPU demo application. Now I found that VPU decoder will cache 5 frames before it decodes the first beginning frame. The total latency of the streaming is about 500ms.

But when I redirect the H264 stream from the demo board to  the cellphone over wifi, and play the stream, to total latency is just about 300ms.

So I guess the cache behavior of the VPU decoder causes the bigger latency. How can I remove the cache behavior to reduce the latency? Is there any params to set in the VPU library to ignore the cache behavior? Many thanks.