[Libav-user] MJPEG quantization tables

[Michael Toon]

Thanks for the response

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

Paragraph 4.2:

"Both type 0 and type 1 JPEG require two quantization tables."

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

This would allow me to set my own tables I presume? I'd prefer to let the encoder decide the tables, all I want is an option to tell it to use two.

>Please remove this from emails sent to a public
>email list.

Apologies, this was auto-generated on the mail server, I'm seeing if webmail makes a difference, otherwise I'll revert to using my personal email account.

Mike

________________________________________
From: Libav-user [libav-user-bounces at ffmpeg.org] On Behalf Of Carl Eugen Hoyos [cehoyos at ag.or.at]
Sent: 15 July 2015 17:28
To: libav-user at ffmpeg.org
Subject: Re: [Libav-user] MJPEG quantization tables

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().

> This message contains confidential information

Please remove this from emails sent to a public
email list.

Carl Eugen

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