Subject: [AVT] MPEG-4 Payload for RTP [MPEG STREAMING]

From: "Siddhartha Gandhi" <[email-masked]>
Date: Mon, 30 Jan 2006 13:35:32 -0600

Consider the following MPEG-4 streaming using RTP, audio ( Payload Type = 97
) and video ( Payload Type = 96 ) in the trace :

Given,

    video_time_scale  = 90000 and audio_time_scale = 44100 

    video_payload_type = 96     and  audio_payload_type = 97

    MPEG-4 video 

        stts = {count, delta} [0] = {5012, 3003}

Hence,  

    27188 (first video packet) - 24188 (second video packet) = 3000 ( this
matches with the delta above )

3000/90000 =1/30 = 0.03333 sec = 33.33 msec. So two consequtive video
packets should have a delay of 33.33 msec.

Two consequtive RTP packets carrying MPEG-4 video payload ( Payload Type =
96) should be 33.33 msec. Infact if we calculate the difference = 5.337154
sec - 5.337140 sec =  0.014 msec != 33.33 msec

Why is this so ?

This time is incremented only after 3 packets containing MPEG-4 video
payload are sent with M-BIT = true by, (3 * 33.33msec) = 99.99 msec

Can anybody tell me the reason as to why Time ( 2nd Column ) is not
incremented in accordance with Timestamp (9th column) ?

Is it related to buffering or something else ?

Appreciate your help.

Thanks

Siddhartha

 

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