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fftools/cmdutils: Use avfilter_pad_count() for AVFilter's number of pads 

Besides being nicer code this also has the advantage of not making
assumptions about the internal implementation: While it is documented
that the AVFilter.inputs and AVFilter.outputs arrays are terminated
by a zeroed sentinel, one is not allowed to infer that one can just
check avfilter_pad_get_name(padarray, i) to see whether one has reached
the sentinel:
It could be that the pointer to the string is contained
in a different structure than AVFilterPad that needs to be accessed
first: return pad->struct->string.
It could be that for small strings an internal buffer in
AVFilterPad is used (to avoid a relocation) whereas for longer strings
an external string is used; this is useful to avoid relocations:
return pad->string_ptr ? pad->string_ptr : pad->interal_string
Or it could be that the name has a default value:
return pad->name ? pad->name : "default"
(This actually made sense for us because the name of most of our
AVFilterPads is just "default"; doing so would save lots of relocations.)

The only thing one is allowed to infer from the existence of the
sentinel is that one is allowed to use avfilter_pad_count() to get
the number of pads. Therefore it is used.

Reviewed-by: Nicolas George <george@nsup.org>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
This commit is contained in:
Andreas Rheinhardt 2021-08-12 17:35:37 +02:00
parent c83a7dd25f
commit d53d48c799
1 changed files with 3 additions and 1 deletions
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4
fftools/cmdutils.c
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@ -1707,12 +1707,14 @@ int show_filters(void *optctx, const char *opt, const char *arg)
while ((filter = av_filter_iterate(&opaque))) {
descr_cur = descr;
for (i = 0; i < 2; i++) {
unsigned nb_pads;
if (i) {
*(descr_cur++) = '-';
*(descr_cur++) = '>';
}
pad = i ? filter->outputs : filter->inputs;
for (j = 0; pad && avfilter_pad_get_name(pad, j); j++) {
nb_pads = avfilter_pad_count(pad);
for (j = 0; j < nb_pads; j++) {
if (descr_cur >= descr + sizeof(descr) - 4)
break;
*(descr_cur++) = get_media_type_char(avfilter_pad_get_type(pad, j));