[FFmpeg-devel] [PATCH v9 4/6] libavcodec/dnxucdec: DNxUncompressed decoder

[Michael Niedermayer]

On Mon, Sep 23, 2024 at 11:16:45AM +0200, Martin Schitter wrote:
[...]

> +static av_cold int dnxuc_decode_init(AVCodecContext *avctx)
> +{
> +    return 0;
> +}

unneeded


[...]

> +/* DNxUncompressed utilizes a very dense bitpack representation of 10bit and 12bit pixel data.
> +
> +Lines of Image data, which look like in their ordinary 8bit counterpart, contain the most
> +significant upper bits of the pixel data. These sections alternate with shorter segments in
> +which the complementary least significant bits of information get packed in a gapless sequence.
> +
> ++----------------------+ +----------------------+ +------------------------+ +----------~
> +|  8 m.s.bits of R[1]  | |  8 m.s.bits of G[1]  | |  8 m.s.bits of B[1]    | | msb R[2]    ... one line
> ++----------------------+ +----------------------+ +------------------------+ +----------~
> +
> ++---------------------------------------------------------------+  +-----------~
> +| +------------+ +------------+ +------------+ +--------------+ |  | +--------~
> +| | 2 lsb R[2] | | 2 lsb B[1] | | 2 lsb G[1] | | 2 lsb R[1]   | |  | | G[3]lsb    ... LSB bits for line
> +| +------------+ +------------+ +------------+ +--------------+ |  | +--------~
> ++---------------------------- one byte ------------------------ +  +-----------~
> +
> +next line of MSB bytes...   */
> +
> +static int unpack_rg10(AVCodecContext *avctx, AVFrame *frame, const AVPacket *pkt)
> +{
> +    int lw, msp, pack, lsp, p_off;
> +    uint16_t r,g,b;
> +
> +    lw = frame->width;
> +
> +    for(int y = 0; y < frame->height; y++){
> +        for(int x = 0; x < frame->width; x++){
> +            msp = pkt->data[y*3*(lw + lw/4) + 3*x];
> +            p_off = y*(3*(lw + lw/4)) + 3*lw + 3*x/4;
> +            pack = pkt->data[p_off];
> +            lsp = (pack >> (3*x%4)*2) & 0x3;
> +            r = (msp << 2) + lsp;
> +            // av_log(0, AV_LOG_DEBUG, "r: %04x, %02x, %02x, %02x, %d\n",
> +            //    r, msp, lsp, pack, p_off);
> +
> +            msp = pkt->data[y*3*(lw + lw/4) + 3*x + 1];
> +            p_off = y*(3*(lw + lw/4)) + 3*lw + (3*x+1)/4;
> +            pack = pkt->data[p_off];
> +            lsp = (pack >> ((3*x+1)%4)*2) & 0x3;
> +            g = (msp << 2) + lsp;
> +            // av_log(0, AV_LOG_DEBUG, "g: %04x, %02x, %02x, %02x, %d\n",
> +            //    g, msp, lsp, pack, p_off);
> +
> +            msp = pkt->data[y*3*(lw + lw/4) + 3*x + 2];
> +            p_off = y*(3*(lw + lw/4)) + 3*lw + (3*x+2)/4;
> +            pack = pkt->data[p_off];
> +            lsp = (pack >> ((3*x+2)%4)*2) & 0x3;
> +            b = (msp << 2) + lsp;
> +            // av_log(0, AV_LOG_DEBUG, "b: %04x, %02x, %02x, %02x, %d\n\n",
> +            //    b, msp, lsp, pack, p_off);
> +

> +            memcpy(&frame->data[2][2*(y*lw + x)], &r, 2);
> +            memcpy(&frame->data[0][2*(y*lw + x)], &g, 2);
> +            memcpy(&frame->data[1][2*(y*lw + x)], &b, 2);

this probably should be AV_WL16() or something like that

thx


[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

The smallest minority on earth is the individual. Those who deny 
individual rights cannot claim to be defenders of minorities. - Ayn Rand
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