Hello,
I'm trying to debug an issue I'm seeing where the filter "acrossfade" produces
a segfault. This seemingly only happens in docker containers, and I am seeing
it when running a rather large filter chain. I'm trying to get to the bottom
of it, but it would be really helpful to understand the context around how
libavfilter fills the filter input fifos. This is the code where I'm seeing
the segfault:
449 AVFrame *in = NULL, *out, *cf[2] = { NULL };
...
474 if (ff_inlink_queued_samples(ctx->inputs[0]) > s->nb_samples) {
475 // consume some samples - this is not a crossfade overlap
486 } else if (ff_inlink_queued_samples(ctx->inputs[1]) >= s->nb_samples) {
487 if (s->overlap) {
488 out = ff_get_audio_buffer(outlink, s->nb_samples);
489 if (!out)
490 return AVERROR(ENOMEM);
491 // NO CHECK IS DONE HERE THAT ENOUGH SAMPLES ARE PRESENT
491 // In our case, there are 0 samples, so
ff_inlink_consume_samples returns early and does not set cf[0]
492 ret = ff_inlink_consume_samples(ctx->inputs[0], s->nb_samples,
s->nb_samples, &cf[0]);
493 if (ret < 0) {
494 av_frame_free(&out);
495 return ret;
496 }
497 // SEGFAULT HERE
498 ret = ff_inlink_consume_samples(ctx->inputs[1], s->nb_samples,
s->nb_samples, &cf[1]);
499 if (ret < 0) {
500 av_frame_free(&out);
501 return ret;
502 }
How does avfilter add samples to an inlink? Does it just fill it randomly or
will it fill input 0 completely and then move on to input 1, 2, 3? Even when I
fix this segfault by ensuring that ff_inlink_queued_samples(ctx->inputs[0]) ==
s->nb_samples, I will still get additional segfaults in the acrossfade code
where ff_inlink_consume_samples returns 0 and does not set the frame pointer.
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