[FFmpeg-devel] [PATCH 3/3] avcodec/mpegvideo_enc: use 64bit multiplication in dct_quantize_trellis_c and dct_quantize_c

[Marton Balint]

On Tue, 7 Jan 2025, Marton Balint wrote:

> Fixes corruption with:
>
> ffmpeg -t 1 -filter_complex "sine=f=21,showwaves=scale=cbrt:mode=line:colors=white:draw=full" -c:v mpeg2video -non_linear_quant 1 -qmin 1 -qmax 1 -cpuflags 0 out.mpg
>
> or
>
> ffmpeg -t 1 -filter_complex "sine=f=21,showwaves=scale=cbrt:mode=line:colors=white:draw=full" -c:v mpeg2video -non_linear_quant 1 -qmin 1 -qmax 1 -trellis 1 out.mpg
>

Ping for this.

Thanks,
Marton

> Signed-off-by: Marton Balint <cus at passwd.hu>
> ---
> libavcodec/mpegvideo_enc.c | 22 +++++++++++-----------
> 1 file changed, 11 insertions(+), 11 deletions(-)
>
> diff --git a/libavcodec/mpegvideo_enc.c b/libavcodec/mpegvideo_enc.c
> index 7001d5a566..d844961a5d 100644
> --- a/libavcodec/mpegvideo_enc.c
> +++ b/libavcodec/mpegvideo_enc.c
> @@ -3984,9 +3984,9 @@ static int dct_quantize_trellis_c(MpegEncContext *s,
>
>     for(i=63; i>=start_i; i--) {
>         const int j = scantable[i];
> -        int level = block[j] * qmat[j];
> +        int64_t level = (int64_t)block[j] * qmat[j];
>
> -        if(((unsigned)(level+threshold1))>threshold2){
> +        if(((uint64_t)(level+threshold1))>threshold2){
>             last_non_zero = i;
>             break;
>         }
> @@ -3994,11 +3994,11 @@ static int dct_quantize_trellis_c(MpegEncContext *s,
>
>     for(i=start_i; i<=last_non_zero; i++) {
>         const int j = scantable[i];
> -        int level = block[j] * qmat[j];
> +        int64_t level = (int64_t)block[j] * qmat[j];
>
> //        if(   bias+level >= (1<<(QMAT_SHIFT - 3))
> //           || bias-level >= (1<<(QMAT_SHIFT - 3))){
> -        if(((unsigned)(level+threshold1))>threshold2){
> +        if(((uint64_t)(level+threshold1))>threshold2){
>             if(level>0){
>                 level= (bias + level)>>QMAT_SHIFT;
>                 coeff[0][i]= level;
> @@ -4587,7 +4587,7 @@ static int dct_quantize_c(MpegEncContext *s,
>                           int16_t *block, int n,
>                           int qscale, int *overflow)
> {
> -    int i, j, level, last_non_zero, q, start_i;
> +    int i, last_non_zero, q, start_i;
>     const int *qmat;
>     const uint8_t *scantable;
>     int bias;
> @@ -4627,10 +4627,10 @@ static int dct_quantize_c(MpegEncContext *s,
>     threshold1= (1<<QMAT_SHIFT) - bias - 1;
>     threshold2= (threshold1<<1);
>     for(i=63;i>=start_i;i--) {
> -        j = scantable[i];
> -        level = block[j] * qmat[j];
> +        const int j = scantable[i];
> +        int64_t level = (int64_t)block[j] * qmat[j];
>
> -        if(((unsigned)(level+threshold1))>threshold2){
> +        if(((uint64_t)(level+threshold1))>threshold2){
>             last_non_zero = i;
>             break;
>         }else{
> @@ -4638,12 +4638,12 @@ static int dct_quantize_c(MpegEncContext *s,
>         }
>     }
>     for(i=start_i; i<=last_non_zero; i++) {
> -        j = scantable[i];
> -        level = block[j] * qmat[j];
> +        const int j = scantable[i];
> +        int64_t level = (int64_t)block[j] * qmat[j];
>
> //        if(   bias+level >= (1<<QMAT_SHIFT)
> //           || bias-level >= (1<<QMAT_SHIFT)){
> -        if(((unsigned)(level+threshold1))>threshold2){
> +        if(((uint64_t)(level+threshold1))>threshold2){
>             if(level>0){
>                 level= (bias + level)>>QMAT_SHIFT;
>                 block[j]= level;
> -- 
> 2.43.0
>
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