Query regarding sub frame synchronization mode for H264 encoder and decoder on Netra DM816x

Hi Swapan,

Your encoder setting   "sliceMode = IH264_SLICEMODE_MBUNIT" means, you are configuring encoder to create a slices based on number of MBs(1020MBs per slice) and not based on bytes. If you want encoder to generate slice for of each 1020 bytes, set sliceMode = IH264_SLICEMODE_BYTES.

and for decoder

>if any slice size if less than 1024 bytes, decoder treats that as end of frame. 

This is the behaviour with latest decoder also.

>with numOutputDataUnits = 17, it gives out decoded output in multiple of numOutputDataUnits (17, 34, 51 MB rows etc). It does not give out slices individually 

This is how decoder is expected to behave. numOutputDataUnits is the freqeuncy in MB rows, the decoder outputs rows.

If you want decoder notification for every row, set numOutputDataUnits = 1. 

Ram

Hi Ram,

Thanks for your response.

I want to clarify few things what I asked for.

I want to use the encoder in IH264_SLICEMODE_MBUNIT only and my slice size is 1020 MBs only (8 slices per frame for 1080P resolution). When the video complexity is very low, say video encoder generates very small amount of bytes (say 300 bytes), in that case encoder does not give out the encoded bit stream for that slice immediately, instead it combine it with the next slices and give the output. I get less than 8 notifications.

For decoder when I configure numOutputDataUnits = 17 for 1080P resolution video I should expect 4 notification per frame. But what I am observing, I get less than 4 notification per frame and the number of notification per frame varies for different frames decoded from the bit stream.

Is there any work around for the decoder to be used when the slice size is less than 1024 bytes and not treating that as end of frame. I don't want to combine multiple slices together as it increases the latency.

Regards,

Swapan

Hi Swapan,

This is a limitation of encode and decoder. We can not notify encoded slices immediately, rather we wait for 1KB of data encoding to be finished  then  notify all the slices present in that 1KB together. we have kept this limitation to ease the implementation and improve the overall cycle performance of encoder and decoder. So in worst case a slice will be notified with a delay of time take n to encode 1KB of data.

May I please know for what application you are trying this?

Regards
Deepak Poddar 

Deepak,

Thanks for your response. I am trying this for a ultra low latency streaming server and client application. With this limitation when there is a very low complexity video the system latency will go high.

What I understand from your response that this limitation is put in the encoder/decoder implementation only. No constraints from the HDVICPs. Is that true? 

Is there any configuration available for the encoder so that the minimum slice output size if at least 1KB.

The other limitation what I mentioned on the decoder output size (giving output in multiple of configured number of rows), can you please look into that as well.

Regards,

Swapan

Swapan,

Please change the encoder configuration as below and see if you can achieve.

sliceMode = IH264_SLICEMODE_MBUNIT  IH264_SLICEMODE_BYTES

sliceUnitSize                  = 1020 1024

By  doing so, each slice size would be of size 1k bytes.

Thanks.

I don't want to wait for 1k bytes data. Even if the bytes generated per slice (in IH264_SLICEMODE_MBUNIT mode ) is less than 1K bytes, can i get the output immediately?

Swapan , I believe that is not possible!!

Deepak, Any comments on this?

Thanks.