Re: [FFmpeg-devel] [PATCH v3] avformat/mov: add option max_stts_delta

[Michael Niedermayer <michael@niedermayer.cc>]

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On Sun, Dec 26, 2021 at 09:30:44PM +0530, Gyan Doshi wrote:
> Very high stts sample deltas may occasionally be intended but usually
> they are written in error or used to store a negative value for dts correction
> when treated as signed 32-bit integers.
> 
> This option lets the user set an upper limit, beyond which the delta is clamped to 1.
> Values greater than the limit if negative when cast to int32 are used to adjust onward dts.
> 
> Unit is the track time scale. Default is UINT_MAX - 48000*10 which
> allows upto a 10 second dts correction for 48 kHz audio streams while
> accommodating 99.9% of uint32 range.
> ---
> v3 changes:
> 
> factored out loop

> simplified correction logic

this looks more sane now
i guess this cannot be easily split into a seperate patch ?


[...]
> @@ -2965,11 +2967,34 @@ static int mov_read_stts(MOVContext *c, AVIOContext *pb, MOVAtom atom)
>          sc->stts_data[i].count= sample_count;
>          sc->stts_data[i].duration= sample_duration;
>  
> -        av_log(c->fc, AV_LOG_TRACE, "sample_count=%d, sample_duration=%d\n",
> +        av_log(c->fc, AV_LOG_TRACE, "sample_count=%u, sample_duration=%u\n",
>                  sample_count, sample_duration);
>  
> -        duration+=(int64_t)sample_duration*(uint64_t)sample_count;
> -        total_sample_count+=sample_count;
> +        /* STTS sample offsets are uint32 but some files store it as int32
> +         * with negative values used to correct DTS delays.
> +           There may be abnormally large values as well. */
> +        if (sample_duration > c->max_stts_delta) {
> +            // assume high delta is a correction if negative when cast as int32
> +            int32_t delta_magnitude = (int32_t)sample_duration;
> +            av_log(c->fc, AV_LOG_WARNING, "Too large sample offset %u in stts entry %u with count %u in st:%d. Clipping to 1.\n",
> +                   sample_duration, i, sample_count, st->index);
> +            sc->stts_data[i].duration = 1;
> +            corrected_dts += (delta_magnitude < 0 ? (int64_t)delta_magnitude : 1) * sample_count;
> +        } else {
> +            corrected_dts += sample_duration * sample_count;
> +        }
> +
> +        current_dts += sc->stts_data[i].duration * sample_count;
> +
> +        if (current_dts > corrected_dts) {
> +            int64_t drift = (current_dts - corrected_dts)/sample_count;

division by 0


thx

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

It is a danger to trust the dream we wish for rather than
the science we have, -- Dr. Kenneth Brown

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