flac demuxer: improve seeking

libavcodec/flac_parser.c

@@ -489,6 +489,14 @@ static int get_best_header(FLACParseContext* fpc, const uint8_t **poutbuf,
                                         &fpc->wrap_buf,
                                         &fpc->wrap_buf_allocated_size);
 
+
+    if (fpc->pc->flags & PARSER_FLAG_USE_CODEC_TS){
+        if (header->fi.is_var_size)
+          fpc->pc->pts = header->fi.frame_or_sample_num;
+        else if (header->best_child)
+          fpc->pc->pts = header->fi.frame_or_sample_num * header->fi.blocksize;
+    }
+
     fpc->best_header_valid = 0;
     fpc->last_fi_valid = 1;
     fpc->last_fi = header->fi;
@@ -516,6 +524,11 @@ static int flac_parse(AVCodecParserContext *s, AVCodecContext *avctx,
             s->duration = fi.blocksize;
             if (!avctx->sample_rate)
                 avctx->sample_rate = fi.samplerate;
+            if (fpc->pc->flags & PARSER_FLAG_USE_CODEC_TS){
+                fpc->pc->pts = fi.frame_or_sample_num;
+                if (!fi.is_var_size)
+                  fpc->pc->pts *= fi.blocksize;
+            }
         }
         *poutbuf      = buf;
         *poutbuf_size = buf_size;

libavformat/flacdec.c

@@ -162,12 +162,57 @@ static int flac_probe(AVProbeData *p)
     return AVPROBE_SCORE_EXTENSION;
 }
 
+static av_unused int64_t flac_read_timestamp(AVFormatContext *s, int stream_index,
+                                             int64_t *ppos, int64_t pos_limit)
+{
+    AVPacket pkt, out_pkt;
+    AVStream *st = s->streams[stream_index];
+    int ret;
+
+    if (avio_seek(s->pb, *ppos, SEEK_SET) < 0)
+        return AV_NOPTS_VALUE;
+
+    av_init_packet(&pkt);
+    st->parser = av_parser_init(st->codec->codec_id);
+    if (!st->parser){
+        return AV_NOPTS_VALUE;
+    }
+    st->parser->flags |= PARSER_FLAG_USE_CODEC_TS;
+
+    for (;;){
+        ret = ff_raw_read_partial_packet(s, &pkt);
+        if (ret < 0){
+            if (ret == AVERROR(EAGAIN))
+                continue;
+            else
+                return AV_NOPTS_VALUE;
+        }
+        av_init_packet(&out_pkt);
+        ret = av_parser_parse2(st->parser, st->codec,
+                               &out_pkt.data, &out_pkt.size, pkt.data, pkt.size,
+                               pkt.pts, pkt.dts, *ppos);
+
+        if (out_pkt.size){
+            int size = out_pkt.size;
+            av_free_packet(&out_pkt);
+            if (st->parser->pts != AV_NOPTS_VALUE){
+                // seeking may not have started from beginning of a frame
+                // calculate frame start position from next frame backwards
+                *ppos = st->parser->next_frame_offset - size;
+                return st->parser->pts;
+            }
+        }
+    }
+    return AV_NOPTS_VALUE;
+}
+
 AVInputFormat ff_flac_demuxer = {
     .name           = "flac",
     .long_name      = NULL_IF_CONFIG_SMALL("raw FLAC"),
     .read_probe     = flac_probe,
     .read_header    = flac_read_header,
     .read_packet    = ff_raw_read_partial_packet,
+    .read_timestamp = flac_read_timestamp,
     .flags          = AVFMT_GENERIC_INDEX,
     .extensions     = "flac",
     .raw_codec_id   = AV_CODEC_ID_FLAC,