H.264 HW Encoder - Issues with Constant bit rate (CBR)

Autonomous Machines Jetson & Embedded Systems Jetson TK1
1

Hello Every one,

I am trying to set constant-bit rate mode, in H.264 encoder in Jetson TK1 for encoding a 720P video. Below is my encoder configuration.

mOutputFormat->setInt32(
            "color-format", OMX_COLOR_FormatYUV420Planar);
    mOutputFormat->setString("mime", MEDIA_MIMETYPE_VIDEO_AVC);
    mOutputFormat->setInt32("width", width);
    mOutputFormat->setInt32("height", height);


    mOutputFormat->setInt32("bitrate", 768000);
    mOutputFormat->setInt32("bitrate-mode", OMX_Video_ControlRateConstant);
    mOutputFormat->setInt32("frame-rate", mFrameRate);
    mOutputFormat->setInt32("i-frame-interval", 1);  // Iframes every 1 secs
    mOutputFormat->setInt32("profile", OMX_VIDEO_AVCProfileBaseline);
    mOutputFormat->setInt32("level", OMX_VIDEO_AVCLevel13);

Here I used “OMX_Video_ControlRateConstant” as bitrate-mode. But the output bitrate from the hardware encoder is not constant. There is no difference between in setting “OMX_Video_ControlRateConstant” and “OMX_Video_ControlRateVariable”.

The bitrate output is always varying. Do you have any ideas about this issue?

Thanks.

2

Hi Gopinath,
Please try to set 1Mbps, 2Mbps. Probably 768kbps is too low for 720p case.

3

Hi DaneLLL,

Thanks for the reply. I have changed the bitrate to 2Mbps. But still I am getting the same results.

This is how, I am checking and printing the bitrate(size).

// get output
        size_t index;
        size_t offset;
        size_t size;
        int64_t presentationTimeUs;
        uint32_t flags;
        status_t err = mCodec->dequeueOutputBuffer(
                &index, &offset, &size, &presentationTimeUs, &flags,
                kTimeout);

        if (err == OK) {
            ALOGE("draining output buffer %d, time = %lld us Size = %d ",
                  index, presentationTimeUs,size);

            if (mNumBuffersEncoded == 0) {
                int64_t timeUs = ALooper::GetNowUs();
                fprintf(stderr, "enc latency = %llu us", timeUs - startTimeUs);
            }

I am expecting the output of dequeue buffer (i.e) size to be same all the time. But In some cases I am getting different size. Please see the below output.

E/AEncode ( 1412): draining output buffer 0, time = 0 us Size = 22 
E/AEncode ( 1412): draining output buffer 1, time = 0 us Size = <b>2728</b> 
E/AEncode ( 1412): draining output buffer 2, time = 33333 us Size = 4097 
E/AEncode ( 1412): draining output buffer 3, time = 66666 us Size = 4098 
E/AEncode ( 1412): draining output buffer 4, time = 100000 us Size = 4093 
E/AEncode ( 1412): draining output buffer 5, time = 133333 us Size = 4096 
E/AEncode ( 1412): draining output buffer 0, time = 166666 us Size = 4096 
E/AEncode ( 1412): draining output buffer 1, time = 200000 us Size = 4096 
E/AEncode ( 1412): draining output buffer 2, time = 233333 us Size = 4096 
E/AEncode ( 1412): draining output buffer 3, time = 266666 us Size = 4096 
E/AEncode ( 1412): draining output buffer 4, time = 300000 us Size = 4096 
E/AEncode ( 1412): draining output buffer 5, time = 333333 us Size = 4095 
E/AEncode ( 1412): draining output buffer 0, time = 366666 us Size = 4097 
E/AEncode ( 1412): draining output buffer 1, time = 400000 us Size = 4097 
E/AEncode ( 1412): draining output buffer 2, time = 433333 us Size = 4090 
E/AEncode ( 1412): draining output buffer 3, time = 466666 us Size = 4097 
E/AEncode ( 1412): draining output buffer 4, time = 500000 us Size = 4097 
E/AEncode ( 1412): draining output buffer 5, time = 533333 us Size = 4097 
E/AEncode ( 1412): draining output buffer 0, time = 566666 us Size = 4097 
E/AEncode ( 1412): draining output buffer 1, time = 600000 us Size = 4097 
E/AEncode ( 1412): draining output buffer 2, time = 633333 us Size = 4097 
E/AEncode ( 1412): draining output buffer 3, time = 666666 us Size = 4097 
E/AEncode ( 1412): draining output buffer 4, time = 700000 us Size = 4097 
E/AEncode ( 1412): draining output buffer 5, time = 733333 us Size = 4097 
E/AEncode ( 1412): draining output buffer 0, time = 766666 us Size = 4097 
E/AEncode ( 1412): draining output buffer 1, time = 800000 us Size = 4097 
E/AEncode ( 1412): draining output buffer 2, time = 833333 us Size = 4097 
E/AEncode ( 1412): draining output buffer 3, time = 866666 us Size = 4097 
E/AEncode ( 1412): draining output buffer 4, time = 900000 us Size = <b>4141</b>

So can you please say, why I am not getting constant bit rate here?

4

Hi Gopinath,
You have to check the bitrate in period, not frame by frame. Since H264 is encoded in I/P/B frames and there are dependency between frames, you will not see all frames with same size.

5

Hi DaneLL,

Thank-you for support. Now I calculated the birrate in period. Now I have two questions.

  1. For 640 x 480, I set bitrate around 700 Kbps and constant bit rate mode. Now I am getting bitrate around 700 Kbps. But my question is, I am seeing bitrate accelerates between 550 Kbps to 800 Kbps. Why I am not getting constant 700 Kbps. (Or this is tolerance range in my period calculation ?) Or else some-other settings like i-frame-interval is creating this issue?

  2. Why Android framework API (MediaCodecInfo.EncoderCapabilities )returns only it supports BITRATE_MODE_VBR for this H.264 encoder?

6

Hi Gopinath,

  1. For 640 x 480, I set bitrate around 700 Kbps and constant bit rate mode. Now I am getting bitrate around 700 Kbps. But my question is, I am seeing bitrate accelerates between 550 Kbps to 800 Kbps. Why I am not getting constant 700 Kbps. (Or this is tolerance range in my period calculation ?) Or else some-other settings like i-frame-interval is creating this issue?
    It is within tolerance. Maybe you can also try the skip-frame modes:
    OMX_Video_ControlRateVariableSkipFrames
    OMX_Video_ControlRateConstantSkipFrames

  2. Why Android framework API (MediaCodecInfo.EncoderCapabilities )returns only it supports BITRATE_MODE_VBR for this H.264 encoder?
    This looks to be about integrating with Android. Need to trace Android frameworks.

7

Hi DaneLLL,

Thank-You.Regarding the second point, the same problem is occurring in Shield tablet (TK1) too (Android Version 5.1.1).