[FFmpeg-devel] Re: [PATCH] libavformat/rtpdec_jpeg.c: Allow sender to include the qtable in fragment offset calculation

[Michael Niedermayer via ffmpeg-devel <ffmpeg-devel@ffmpeg.org>]

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Hi Hayden

On Tue, Dec 09, 2025 at 12:57:40PM -0500, Hayden Myers via ffmpeg-devel wrote:
> Signed-off-by: Hayden Myers <haydenm315@gmail.com>
> ---
>  libavformat/rtpdec_jpeg.c | 22 +++++++++++++++++++---
>  1 file changed, 19 insertions(+), 3 deletions(-)
> 
> diff --git a/libavformat/rtpdec_jpeg.c b/libavformat/rtpdec_jpeg.c
> index 4d9ee0d754..871f3a732e 100644
> --- a/libavformat/rtpdec_jpeg.c
> +++ b/libavformat/rtpdec_jpeg.c
> @@ -353,9 +353,25 @@ static int jpeg_parse_packet(AVFormatContext *ctx, PayloadContext *jpeg,
>      }
>  
>      if (off != avio_tell(jpeg->frame) - jpeg->hdr_size) {
> -        av_log(ctx, AV_LOG_ERROR,
> -               "Missing packets; dropping frame.\n");
> -        return AVERROR(EAGAIN);
> +        /* The fragment offset may include the quant table data. Allow the
> +         * offset to differ by the size of the quant header and table.
> +         */
> +

> +        // Default to 2 * 64 byte tables for 8 bit precision.
> +        uint8_t qtable_len =  128;

exact length is not needed here, int tends to lead to fewer surprises


> +
> +        // Use the q table len value stored in the ctx
> +        if (q >= 127 && q < 255)
> +            qtable_len = jpeg->qtables_len[q-128];

127-128 is -1 thus results in out of array. jpeg->qtables_len[-1];

thx

[...]

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Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Democracy is the form of government in which you can choose your dictator

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