[Libav-user] MJPEG quantization tables

[Carl Eugen Hoyos]

Michael Toon <michael.toon at ...> writes:

> I am using the encoder libs to encode MJPEG video 
> which I am packaging up to send via RTP. The 
> encoded bit stream that I generate only appears 
> to have a single quantization table defined, 
> however the RTP payload format specifies that if 
> using custom quantization tables there should be 
> two separate quantization tables for luma and 
> chroma.

Could you point me to the paragraph in the rfc 
where this is suggested? I seem to have missed 
it...

> Having separate tables seems to make sense to try 
> and gain most encoding efficiency, especially 
> since I need to transmit two tables regardless. 

> Is there a reason why the MJPEG codec only 
> generates a single table

(I don't know.)

> is there an option that I can to use separate 
> tables?

Please see AVCodecContext->intra_matrix (for luma) 
and av_codec_set_chroma_intra_matrix().

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Carl Eugen