[Libav-user] MJPEG Quantization tables

[Richard Hussong]

Sorry, but I've never modified those values myself and I don't know how
they work. I think you'll have to read the source code for the JPEG encoder
to find out.

- Richard

On Mon, May 18, 2020 at 1:37 PM Виктор Мулин <17sep96 at gmail.com> wrote:

> Thanks for the answer.
> intra_matrix and inter_matrix are of type uint16_t, and tables from
> jpegtables.c are of type uint8_t. What to do? Make a cast of uint8_t * to
> uint16_t * or define a new array of type uint16_t by filling it with values
> from standard tables?
> Will these tables be added to the output file automatically after I
> specify array references in the AVCodecContext structure?
>
> пн, 18 мая 2020 г. в 19:54, Richard Hussong <rhussong at westpond.com>:
>
>>
>>
>> On Mon, May 18, 2020 at 7:38 AM Виктор Мулин <17sep96 at gmail.com> wrote:
>>
>>> Hello! When using the mjpeg codec to convert an image from bmp to jpg
>>> format, a picture with one quantization table is created. I need two
>>> standard tables described in the jpeg iso / iec 10918-1 T.81 standard in
>>> Appendix K.1 and K.2 to be added to the output image file. I also found
>>> them in the ffmpeg source codes (jpegtables.c -> std_luminance_quant_tbl
>>> and jpegtables.c -> std_chrominance_quant_tbl [url:
>>> https://ffmpeg.org/doxygen/trunk/jpegtables_8c_source.html]. I looked
>>> through the mailing list archive and found old solutions (
>>> https://ffmpeg.org/pipermail/libav-user/2015-July/008318.html), but now
>>> the av_codec_set_chroma_intra_matrix () function is declared depricated.
>>> How do I get what I want? How to set intra_matrix, chroma_intra_matrix and
>>> inter_matrix (in the description they are almost the same)?
>>>
>>
>> The intra_matrix and inter_matrix can now be set directly in the
>> AVCodecContext structure. See
>> https://ffmpeg.org/doxygen/trunk/structAVCodecContext.html, and search
>> for "intra_matrix" and "inter_matrix".
>>
>> P.S .: Sorry, I don't speak English well. I use google translator.
>>>
>>
>> Don't worry - what you wrote is clear enough.
>>
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