[FFmpeg-devel] [PATCH] af_hdcd: Improve HDCD detection

Michael Niedermayer michael at niedermayer.cc
Sun Jul 24 01:41:26 EEST 2016


On Sun, Jul 17, 2016 at 12:34:12PM -0500, Burt P wrote:
> HDCD is only "detected" if a valid code is active in both
> channels simultaneously, as described here:
> https://hydrogenaud.io/index.php/topic,79427.msg900371.html#msg900371
> 
> Signed-off-by: Burt P <pburt0 at gmail.com>
> ---
>  libavfilter/af_hdcd.c | 34 ++++++++++++++++++++++++----------
>  1 file changed, 24 insertions(+), 10 deletions(-)
> 
> diff --git a/libavfilter/af_hdcd.c b/libavfilter/af_hdcd.c
> index 6f0db71..4b48967 100644
> --- a/libavfilter/af_hdcd.c
> +++ b/libavfilter/af_hdcd.c
> @@ -818,15 +818,25 @@ static const int32_t gaintab[] = {
>  
>  typedef struct {
>      uint64_t window;
> -    unsigned char readahead, arg, control;
> -    int running_gain;
> -    unsigned sustain, sustain_reset;
> -    int code_counterA;
> -    int code_counterA_almost; /* looks like an A code, but a bit expected to be 0 is 1 */
> -    int code_counterB;
> +    unsigned char readahead;
> +
> +    /* arg is set when a packet prefix is found.
> +     * control is the active control code, where
> +     * bit 0-3: target_gain, 4-bit (3.1) fixed-point value
> +     * bit 4  : peak_extend
> +     * bit 5  : transient_filter
> +     * bit 6,7: always zero */
> +    unsigned char arg, control;
> +    unsigned sustain, sustain_reset; /* code detect timer */
> +
> +    int running_gain; /* 11-bit (3.8) fixed point, extended from target_gain */
> +
> +    int code_counterA;            /* 8-bit format packet */
> +    int code_counterA_almost;     /* looks like an A code, but a bit expected to be 0 is 1 */
> +    int code_counterB;            /* 16-bit format packet, 8-bit code, 8-bit XOR of code */
>      int code_counterB_checkfails; /* looks like a B code, but doesn't pass the XOR check */
> -    int code_counterC;
> -    int code_counterC_unmatched; /* told to look for a code, but didn't find one */
> +    int code_counterC;            /* packet prefix was found, expect a code */
> +    int code_counterC_unmatched;  /* told to look for a code, but didn't find one */
>  
>      /* For user information/stats, pulled up into HDCDContext
>       * by filter_frame() */
> @@ -1096,7 +1106,7 @@ static int filter_frame(AVFilterLink *inlink, AVFrame *in)
>      AVFrame *out;
>      const int16_t *in_data;
>      int32_t *out_data;
> -    int n, c;
> +    int n, c, detect;
>  
>      out = ff_get_audio_buffer(outlink, in->nb_samples);
>      if (!out) {
> @@ -1112,6 +1122,7 @@ static int filter_frame(AVFilterLink *inlink, AVFrame *in)
>          out_data[n] = in_data[n];
>      }
>  
> +    detect = 0;
>      s->det_errors = 0;
>      for (c = 0; c < inlink->channels; c++) {
>          hdcd_state_t *state = &s->state[c];
> @@ -1120,11 +1131,14 @@ static int filter_frame(AVFilterLink *inlink, AVFrame *in)
>          s->uses_peak_extend |= !!state->count_peak_extend;
>          s->uses_transient_filter |= !!state->count_transient_filter;
>          s->max_gain_adjustment = FFMIN(s->max_gain_adjustment, GAINTOFLOAT(state->max_gain));
> -        s->hdcd_detected |= state->code_counterB || state->code_counterA;
> +        if (state->sustain) detect++;
>          s->det_errors += state->code_counterA_almost
>              + state->code_counterB_checkfails
>              + state->code_counterC_unmatched;
>      }
> +    /* HDCD is detected if a valid packet is active in all (both)
> +     * channels at the same time. */
> +    if (detect == inlink->channels) s->hdcd_detected = 1;

this looks like 2 unrelated changes
one is improving documentation the other is changing ths detect code
can you split these in 2 patches ?

thx


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

The bravest are surely those who have the clearest vision
of what is before them, glory and danger alike, and yet
notwithstanding go out to meet it. -- Thucydides
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