Re: [FFmpeg-devel] [PATCH] lavc/av1*: fix exporting framerate

[James Almer <jamrial@gmail.com>]

On 5/14/2023 4:39 PM, Anton Khirnov wrote:
> * take num_ticks_per_picture_minus_1 into account, since that is a part
>    of the framerate computation
> * stop exporting num_ticks_per_picture_minus_1 into
>    AVCodecContext.ticks_per_frame, as that field is used for other
>    purposes (in conjunction with repeat_pict, which is not used at all by
>    av1)
> ---
>   libavcodec/Makefile     |  2 +-
>   libavcodec/av1_parse.c  | 14 ++++++++++++++
>   libavcodec/av1_parse.h  |  3 +++
>   libavcodec/av1_parser.c | 13 +++++++++----
>   libavcodec/av1dec.c     | 16 ++++++++--------
>   5 files changed, 35 insertions(+), 13 deletions(-)
> 
> diff --git a/libavcodec/Makefile b/libavcodec/Makefile
> index 3cf4444b7e..9587e56493 100644
> --- a/libavcodec/Makefile
> +++ b/libavcodec/Makefile
> @@ -1143,7 +1143,7 @@ OBJS-$(CONFIG_AC3_PARSER)              += aac_ac3_parser.o ac3tab.o \
>                                             ac3_channel_layout_tab.o
>   OBJS-$(CONFIG_ADX_PARSER)              += adx_parser.o
>   OBJS-$(CONFIG_AMR_PARSER)              += amr_parser.o
> -OBJS-$(CONFIG_AV1_PARSER)              += av1_parser.o
> +OBJS-$(CONFIG_AV1_PARSER)              += av1_parser.o av1_parse.o
>   OBJS-$(CONFIG_AVS2_PARSER)             += avs2.o avs2_parser.o
>   OBJS-$(CONFIG_AVS3_PARSER)             += avs3_parser.o
>   OBJS-$(CONFIG_BMP_PARSER)              += bmp_parser.o
> diff --git a/libavcodec/av1_parse.c b/libavcodec/av1_parse.c
> index 59ea0bc6e7..26b70845f2 100644
> --- a/libavcodec/av1_parse.c
> +++ b/libavcodec/av1_parse.c
> @@ -108,3 +108,17 @@ void ff_av1_packet_uninit(AV1Packet *pkt)
>       av_freep(&pkt->obus);
>       pkt->obus_allocated = pkt->obus_allocated_size = 0;
>   }
> +
> +AVRational ff_av1_framerate(int ticks_per_frame, int units_per_tick,
> +                            int time_scale)
> +{
> +    AVRational fr = (AVRational){ 0, 1 };
> +
> +    if (ticks_per_frame && units_per_tick && time_scale &&
> +        ticks_per_frame < INT_MAX / units_per_tick) {

av_reduce takes int64_t as input, so you could just cast units_per_tick.

> +        av_reduce(&fr.den, &fr.num, units_per_tick * ticks_per_frame,
> +                  time_scale, INT_MAX);
> +    }
> +
> +    return fr;
> +}
> diff --git a/libavcodec/av1_parse.h b/libavcodec/av1_parse.h
> index f4a5d2830e..11f9c77de4 100644
> --- a/libavcodec/av1_parse.h
> +++ b/libavcodec/av1_parse.h
> @@ -181,4 +181,7 @@ static inline int get_obu_bit_length(const uint8_t *buf, int size, int type)
>       return size;
>   }
>   
> +AVRational ff_av1_framerate(int ticks_per_frame, int units_per_tick,
> +                            int time_scale);
> +
>   #endif /* AVCODEC_AV1_PARSE_H */
> diff --git a/libavcodec/av1_parser.c b/libavcodec/av1_parser.c
> index 14dae92fe9..0d81c29e63 100644
> --- a/libavcodec/av1_parser.c
> +++ b/libavcodec/av1_parser.c
> @@ -21,6 +21,8 @@
>    */
>   
>   #include "libavutil/avassert.h"
> +
> +#include "av1_parse.h"
>   #include "cbs.h"
>   #include "cbs_av1.h"
>   #include "parser.h"
> @@ -162,10 +164,13 @@ static int av1_parser_parse(AVCodecParserContext *ctx,
>       avctx->color_trc = (enum AVColorTransferCharacteristic) color->transfer_characteristics;
>       avctx->color_range = color->color_range ? AVCOL_RANGE_JPEG : AVCOL_RANGE_MPEG;
>   
> -    if (seq->timing_info_present_flag) {
> -        const AV1RawTimingInfo *timing = &seq->timing_info;
> -        av_reduce(&avctx->framerate.den, &avctx->framerate.num,
> -                  timing->num_units_in_display_tick, timing->time_scale, INT_MAX);
> +    if (seq->timing_info_present_flag                                &&
> +        seq->timing_info.num_ticks_per_picture_minus_1 < INT_MAX - 1 &&
> +        seq->timing_info.num_units_in_display_tick     < INT_MAX     &&
> +        seq->timing_info.time_scale                    < INT_MAX) {

You could pass all uint32_t values as they are and check the return 
value of av_reduce(). If it's 0 (non exact result) then don't set 
avctx->framerate (or set it to { 0, 1 }, whatever is cleaner).
There could be samples with bitstream values > INT_MAX where the reduced 
AVRational is still within INT_MAX for num and den.

> +        avctx->framerate = ff_av1_framerate(seq->timing_info.num_ticks_per_picture_minus_1 + 1,
> +                                            seq->timing_info.num_units_in_display_tick,
> +                                            seq->timing_info.time_scale);
>       }
>   
>   end:
> diff --git a/libavcodec/av1dec.c b/libavcodec/av1dec.c
> index c90c9c1a69..dae1d8e8da 100644
> --- a/libavcodec/av1dec.c
> +++ b/libavcodec/av1dec.c
> @@ -26,6 +26,7 @@
>   #include "libavutil/pixdesc.h"
>   #include "libavutil/opt.h"
>   #include "avcodec.h"
> +#include "av1_parse.h"
>   #include "av1dec.h"
>   #include "atsc_a53.h"
>   #include "bytestream.h"
> @@ -709,14 +710,13 @@ static int set_context_with_sequence(AVCodecContext *avctx,
>       }
>       avctx->sample_aspect_ratio = (AVRational) { 1, 1 };
>   
> -    if (seq->timing_info.num_units_in_display_tick &&
> -        seq->timing_info.time_scale) {
> -        av_reduce(&avctx->framerate.den, &avctx->framerate.num,
> -                  seq->timing_info.num_units_in_display_tick,
> -                  seq->timing_info.time_scale,
> -                  INT_MAX);
> -        if (seq->timing_info.equal_picture_interval)
> -            avctx->ticks_per_frame = seq->timing_info.num_ticks_per_picture_minus_1 + 1;
> +    if (seq->timing_info_present_flag                                &&
> +        seq->timing_info.num_ticks_per_picture_minus_1 < INT_MAX - 1 &&
> +        seq->timing_info.num_units_in_display_tick     < INT_MAX     &&
> +        seq->timing_info.time_scale                    < INT_MAX) {
> +        avctx->framerate = ff_av1_framerate(seq->timing_info.num_ticks_per_picture_minus_1 + 1,
> +                                            seq->timing_info.num_units_in_display_tick,
> +                                            seq->timing_info.time_scale);
>       }
>   
>       return 0;
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