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a2e7642d3c
Until now, feeding packets to the decoder in advance was done for text subtitles only. This was possible because libass buffers all subtitle data anyway (in ASS_Track). sd_lavc, responsible for bitmap subs, does not do this. But it can buffer a small number of subtitle frames ahead. Enable this. Repurpose the sub_accept_packets_in_advance(). Instead of "can take all packets" it means "can take 1 packet" now. (The old meaning is still needed locally in dec_sub.c; keep it there.) It asks the decoder whether there is place for at least 1 subtitle packet. sd_lavc implements it and returns true if its internal fixed-size subtitle queue still has a free slot. (The implementation of this in dec_sub.c isn't entirely clean. For one, decode_chain() ignores this mechanism, so it's implied that bitmap subtitles do not use the subtitle filter chain in any advanced way.) Also fix 2 bugs in the sd_lavc queue handling. Subtitles must be checked in reverse, because the first entry will often have endpts==NOPTS, which would always match. alloc_sub() must cycle the queue buffer, because it reuses memory allocations (like sub.imgs) by design.