Re: [FFmpeg-devel] [PATCH 07/23] fftools/sync_queue: allow requesting a specific number of audio samples

[James Almer <jamrial@gmail.com>]

On 3/25/2023 4:15 PM, Anton Khirnov wrote:
> +static void offset_audio(AVFrame *f, int nb_samples)
> +{
> +    const int planar = av_sample_fmt_is_planar(f->format);
> +    const int planes = planar ? f->ch_layout.nb_channels : 1;
> +    const int    bps = av_get_bytes_per_sample(f->format);
> +    const int offset = nb_samples * bps * (planar ? 1 : f->ch_layout.nb_channels);
> +
> +    av_assert0(bps > 0);
> +    av_assert0(nb_samples < f->nb_samples);
> +
> +    for (int i = 0; i < planes; i++) {
> +        f->extended_data[i] += offset;

This apparently can end up unaligned. It's (afaict) the source of the 
segmentation fault Michael reported. If you run his command with 
-cpuflags 0 it doesn't crash.
You may need to allocate a new frame and copy the data instead of making 
a reference in such scenarios.

> +        if (i < FF_ARRAY_ELEMS(f->data))
> +            f->data[i] = f->extended_data[i];
> +    }
> +    f->linesize[0] -= offset;
> +    f->nb_samples  -= nb_samples;
> +    f->duration     = av_rescale_q(f->nb_samples, (AVRational){ 1, f->sample_rate },
> +                                   f->time_base);
> +    f->pts         += av_rescale_q(nb_samples,    (AVRational){ 1, f->sample_rate },
> +                                   f->time_base);
> +}
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