H.264 latency

Martin Fletzer15516

Hi,

is low latency possible with the demo H.264 codec of TI?

I tried the encode-decode demo on the DM6467, and decoding takes more than one second. Can the latency be improved by configuration changes?

What are the reasons for this latency?

Thanks,

Martin

over 15 years ago

0 Juan Gonzales over 15 years ago

TI__Mastermind 37340 points

mmm, what size of frame are you trying to decode; our demos are encoding and decoding at 30 fps I believe, that would imply each frame takes 1/30th sec.

0 Martin Fletzer15516 over 15 years ago in reply to Juan Gonzales

Prodigy 90 points

I use PAL. The processing time for decoding is not the problem.

But I have to call 16 times Vdec2_process() before Vdec2_getDisplayBuf() returns a valid buffer. This behavior is responsible for most of the latency.

The codec requires Vdec2_getMinOutBufs() buffers. Can the number of required buffers be controlled?

Thanks,

Martin

0 Juan Gonzales over 15 years ago in reply to Martin Fletzer15516

TI__Mastermind 37340 points

16 sounds high. Are you sure you are priming the codec correctly (e.g. processed one successful frame before calling on Vdec2_getMinOutBufs)? I would refer to the decode demo; it has source code to do the priming correctly as well as comments as to why you need to do this.

0 Martin Fletzer15516 over 15 years ago in reply to Juan Gonzales

Prodigy 90 points

Since I use the encode-decode demo, priming should be right. I only changed the demo to use PAL instead of 720p. Vdec2_getMinOutBufs returns 17.

I will try if the decode demo works better.

Edit: Vdec2_getMinOutBufs() also returns 17 for the decode demo.

Thanks,

Martin

0 Kapil Ahuja over 15 years ago in reply to Martin Fletzer15516

TI__Intellectual 1970 points

Martin,

As per the H264 standard, there could be re-ordering of the display frames. Hence for D1 you get the first frame after the 17th process call. If you are deocding 1920x1080p you will get the first frame after the 5th process call. If you want to change this default value, you have to use extended params, and set the display_delay field. But note that for some streams which require that the decoder holds upto 16 frames(for D1) or 4 frames (for 1080HD) to know the correct display order; the output will not be standard compliant.

Regards,

Kapil

0 zhifei zhang over 14 years ago

Prodigy 240 points

Hi, have you managed to reduce the latency of encode-decode? I come across the same problem. Do you have any advice?

0 Martin Fletzer15516 over 14 years ago in reply to zhifei zhang

Prodigy 90 points

Low latency requires only little changes.

It's been a while since I had this problem, but I think you have to use adapted IH264VDEC_Params. I use:

IH264VDEC_Params       decH264Params = {
    my_Vdec2_Params_DEFAULT,
    1,                //displayDelay
    Level3,         //presetLevelIdc
    Profile_Any, //presetProfileIdc
    1                 //temporalDirModePred
};

0 zhifei zhang over 14 years ago in reply to Martin Fletzer15516

Prodigy 240 points

thank you,Martin Fletzer

But I cannot find the definition of IH264VDEC_Params. Could you tell me the data structure of IH264VDEC_Params ?

0 Martin Fletzer15516 over 14 years ago in reply to zhifei zhang

Prodigy 90 points

Hi,

look at http://focus.ti.com/lit/ug/spruet5/spruet5.pdf

Martin

0 zhifei zhang over 14 years ago in reply to Martin Fletzer15516

Prodigy 240 points

well, Martin,

I have found the defination of IH264VDEC_Params, but "temporalDirModePred" is not included in the IH264VDEC_Params.

I use the extended params like this :

VIDDEC2_Params *params = Vdec2_Params_DEFAULT;

IH264VDEC_Params decH264Params;

decH264Params.viddecParams = *params;

decH264Params.displayDelay =1;

decH264Params.presetLevelIdc = Level3;

decH264Params.presetProfileIdc = Profile_Any;

params->size = sizeof(IH264VDEC_Params);

Vdec2_create(hEngine,codecname,(VIDDEC2_Params *)&decH264Params,dynParams) // this is successfully created

but then, Vdec2_process returns error.

Could you tell me where goes wrong? Is temporalDirModePred necessary for the extended params?

Thank you

0 zhifei zhang over 14 years ago in reply to Martin Fletzer15516

Prodigy 240 points

And may I know the version of your dvsdk?

0 Martin Fletzer15516 over 14 years ago in reply to zhifei zhang

Prodigy 90 points

I use version 3.10.00.19

I took the structure from the header file located at ./dvsdk_3_10_00_19/cs2dm6467_1_00_00_10/packages/ti/sdo/codecs/h264dec/ih264vdec.h.

There is a flag for temporal direct mode prediction enable/disable listed.

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H.264 latency