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Video quality will be bad when IDR frame appear.

Tracy lee
Expert 1505 points

Hi ALL:

           I have found one issue that the video quality(Both MPEG4 and H264) will be bad when IDR frame appear.  This happened for both live streaming and cptured file, I think there maybe something wrong with codec.

          I have build a sample file with MPEG4 CBR 256Kbps, 15f/s, IDR interval is 30f/s, no I frames, that means we will encode one IDR frame every 2 seconds, you will find the video quality will be bad every two seconds.

          4331.MPEG4_VGA_GOV30_FPS15_VeryLow.mp4

          BTW, both CBR and VBR have the same issue, even we set a high quality level or high bitrate, it still exist.

           Anyone who can help on this?

          Any comments would be appreciated!

  • 0
    Expert 1640 points

    Hi Tracy,

    I assume that for MPEG4 you are doing a force I frame every 2 seconds. 

    Also, seeing that you are encoding VGA at 256Kbps, it's understandable that the Iframe quality is blocky. it would be advisable for you to go for either of the low bitrate RC (LBR1, LBR2) algorithms that we have. With those in place, you can tune the desired quality of the I -frame using the IFrameBiasFactor and PFrameBiasFactor parameters. In the attached video, it seems you are encoding with the Q fixed at 21. For the same bitrate, have you seen any quality difference if the Q is allowed to vary over the entire range?

    For the higher bitrate streams that show this issue, can you include a complete set of parameters that are used in that case.

    Regards,

     

    Akshay

     

  • 0
    TI__Genius 17215 points

    Hi Tracy,

    For H.264, Have you checked http://processors.wiki.ti.com/index.php/DM36x_Rate_Control_Modes ? There are many other modes which can be helpful in diff kind of application. One generic advise is to use rcAlgo = 5 instead of rcAlgo = 0.

    Will get back on Mpeg4.

    regards

    yashwant

  • 0 in reply to Yashwant Dutt
    TI__Genius 17215 points

    Akshay has already given reply on Mpeg4.

    regards

    YD