[FFmpeg-devel] [PATCH 2/4] avdevice/decklink_dec: Extraction of luma from V210 VANC modularized

[Marton Balint]

On Thu, 31 Aug 2017, kjeyapal at akamai.com wrote:

> From: Karthick J <kjeyapal at akamai.com>
>
> In preparation to support multiple VANC data decode
>
> Signed-off-by: Karthick J <kjeyapal at akamai.com>
> ---
> libavdevice/decklink_dec.cpp | 31 ++++++++++++++++++-------------
> 1 file changed, 18 insertions(+), 13 deletions(-)
>
> diff --git a/libavdevice/decklink_dec.cpp b/libavdevice/decklink_dec.cpp
> index 40ef655..0b88fc8 100644
> --- a/libavdevice/decklink_dec.cpp
> +++ b/libavdevice/decklink_dec.cpp
> @@ -106,6 +106,18 @@ static void get_vanc_lines(int bmd_field_dominance, int height, int *field0_vanc
>     }
> }
> 
> +/* The 10-bit VANC data is packed in V210, we only need the luma component. */
> +static void extract_luma_from_v210(uint16_t *dst, const uint8_t *src, int width)
> +{
> +    int i;
> +    for (i = 0; i < width / 3; i += 3) {
> +        *dst++ = (src[1] >> 2) + ((src[2] & 15) << 6);
> +        *dst++ =  src[4]       + ((src[5] &  3) << 8);
> +        *dst++ = (src[6] >> 4) + ((src[7] & 63) << 4);
> +        src += 8;
> +    }
> +}
> +
> static uint8_t calc_parity_and_line_offset(int line)
> {
>     uint8_t ret = (line < 313) << 5;
> @@ -221,19 +233,10 @@ static uint8_t* teletext_data_unit_from_ancillary_packet(uint16_t *py, uint16_t
>     return tgt;
> }
> 
> -static uint8_t* teletext_data_unit_from_vanc_data(uint8_t *src, uint8_t *tgt, int64_t wanted_lines)
> +static uint8_t* teletext_data_unit_from_vanc_data(uint16_t *py, uint8_t *tgt, int64_t wanted_lines)
> {
> -    uint16_t y[1920];
> -    uint16_t *py = y;
> -    uint16_t *pend = y + 1920;
> -    /* The 10-bit VANC data is packed in V210, we only need the luma component. */
> -    while (py < pend) {
> -        *py++ = (src[1] >> 2) + ((src[2] & 15) << 6);
> -        *py++ =  src[4]       + ((src[5] &  3) << 8);
> -        *py++ = (src[6] >> 4) + ((src[7] & 63) << 4);
> -        src += 8;
> -    }
> -    py = y;
> +    uint16_t *pend = py + 1920;
> +
>     while (py < pend - 6) {
>         if (py[0] == 0 && py[1] == 0x3ff && py[2] == 0x3ff) {           // ancillary data flag
>             py += 3;
> @@ -570,8 +573,10 @@ HRESULT decklink_input_callback::VideoInputFrameArrived(
>                     for (i = 0; i <= vanc_end; i++) {
>                         uint8_t *buf;
>                         if (vanc->GetBufferForVerticalBlankingLine(i, (void**)&buf) == S_OK) {
> +                            uint16_t luma_vanc[4096]; // Allocated for highest width (4K)

I think we only have vanc numbers until resolution of 1920 width, so that 
should be enough. Probably better to add an av_assert which checks if 
frame width is less or equal to FF_ARRAY_ELEMS(luma_vanc).

> +                            extract_luma_from_v210(luma_vanc, buf, videoFrame->GetWidth());
>                             if (videoFrame->GetWidth() == 1920) {
> -                                txt_buf = teletext_data_unit_from_vanc_data(buf, txt_buf, ctx->teletext_lines);
> +                                txt_buf = teletext_data_unit_from_vanc_data(luma_vanc, txt_buf, ctx->teletext_lines);
>                                 if (txt_buf - txt_buf0 > 1611) {   // ensure we still have at least 1920 bytes free in the buffer
>                                     av_log(avctx, AV_LOG_ERROR, "Too many OP47 teletext packets.\n");
>                                     break;

Regards,
Marton