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lavfi: add comments to explain the negotiation loop.

This commit is contained in:
Nicolas George 2013-05-06 14:09:53 +02:00
parent 78d16b6a51
commit 4582e4c086
1 changed files with 19 additions and 2 deletions
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21
libavfilter/avfiltergraph.c
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@ -316,12 +316,24 @@ static int formats_declared(AVFilterContext *f)
return 1;
}
/**
* Perform one round of query_formats() and merging formats lists on the
* filter graph.
* @return >=0 if all links formats lists could be queried and merged;
* AVERROR(EAGAIN) some progress was made in the queries or merging
* and a later call may succeed;
* AVERROR(EIO) (may be changed) plus a log message if no progress
* was made and the negotiation is stuck;
* a negative error code if some other error happened
*/
static int query_formats(AVFilterGraph *graph, AVClass *log_ctx)
{
int i, j, ret;
int scaler_count = 0, resampler_count = 0;
int count_queried = 0, count_merged = 0, count_already_merged = 0,
count_delayed = 0;
int count_queried = 0; /* successful calls to query_formats() */
int count_merged = 0; /* successful merge of formats lists */
int count_already_merged = 0; /* lists already merged */
int count_delayed = 0; /* lists that need to be merged later */
for (i = 0; i < graph->nb_filters; i++) {
AVFilterContext *f = graph->filters[i];
@ -464,6 +476,11 @@ static int query_formats(AVFilterGraph *graph, AVClass *log_ctx)
if (count_delayed) {
AVBPrint bp;
/* if count_queried > 0, one filter at least did set its formats,
that will give additional information to its neighbour;
if count_merged > 0, one pair of formats lists at least was merged,
that will give additional information to all connected filters;
in both cases, progress was made and a new round must be done */
if (count_queried || count_merged)
return AVERROR(EAGAIN);
av_bprint_init(&bp, 0, AV_BPRINT_SIZE_AUTOMATIC);