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H.264 decoder displayDelay

Bernard Vachon
Intellectual 465 points

The following TI wiki page (http://processors.wiki.ti.com/index.php/Latency_Measurement_on_Capture_Encode_Decode_Display_Demo) discusses video latency measurements through the 81xx. I have gone through the source code and noticed the example modifies the 'displayDelay' attribute of the h.264 decoder structure. The default value for this attribute is 5 frames, but the example sets its value to 0 frames, thus reducing the latency by 80ms at 60fps. The fact that the default is 5 makes me think there is a downside to setting it to 0, but have not found any documentation on the topic. Can anyone comment on the use of this attribute?

Bernard

  • 0
    TI__Prodigy 505 points

    Bernard,

    The attribute displayDelay decides the delay ( in terms of frames) when the decoder should return the decoded frame to the application.  If the displayDelay  is set to 5, then the decoder sets the delay to 5 frames. The default value of displayDelay  is IVIDDEC3_DISPLAY_DELAY_AUTO , where the decoder decides the display delay. The whole idea for Latency measurement on Capture Encode Decode Display demo is to measure the latency incurred due to the OMX components, codecs and framework etc, hence the displayDelay  is set to 0, where the frames are displayed in decode order without any delay.

    The downside of this setting displayDelay  to 0 is, the displayed frames will be out of order if the input sequence contains any B frames.

    Regards

    Ansari