WebVTT demuxer and decoder.

libavformat/webvttdec.c

@@ -0,0 +1,188 @@
+/*
+ * Copyright (c) 2012 Clément Bœsch
+ *
+ * This file is part of FFmpeg.
+ *
+ * FFmpeg is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * FFmpeg is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with FFmpeg; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+/**
+ * @file
+ * WebVTT subtitle demuxer
+ * @see http://dev.w3.org/html5/webvtt/
+ */
+
+#include "avformat.h"
+#include "internal.h"
+#include "subtitles.h"
+#include "libavutil/bprint.h"
+#include "libavutil/intreadwrite.h"
+
+typedef struct {
+    FFDemuxSubtitlesQueue q;
+} WebVTTContext;
+
+static int webvtt_probe(AVProbeData *p)
+{
+    const uint8_t *ptr = p->buf;
+
+    if (AV_RB24(ptr) == 0xEFBBBF)
+        ptr += 3;  /* skip UTF-8 BOM */
+    if (!strncmp(ptr, "WEBVTT", 6) &&
+        (!ptr[6] || strchr("\n\r\t ", ptr[6])))
+        return AVPROBE_SCORE_MAX;
+    return 0;
+}
+
+static int64_t read_ts(const char *s)
+{
+    int hh, mm, ss, ms;
+    if (sscanf(s, "%u:%u:%u.%u", &hh, &mm, &ss, &ms) == 4) return (hh*3600 + mm*60 + ss) * 1000 + ms;
+    if (sscanf(s,    "%u:%u.%u",      &mm, &ss, &ms) == 3) return (          mm*60 + ss) * 1000 + ms;
+    return AV_NOPTS_VALUE;
+}
+
+static int64_t extract_cue(AVBPrint *buf, AVIOContext *pb)
+{
+    int prev_chr_is_eol = 0;
+    int64_t pos = avio_tell(pb);
+
+    av_bprint_clear(buf);
+    for (;;) {
+        char c = avio_r8(pb);
+        if (!c)
+            break;
+        if (c == '\r' || c == '\n') {
+            if (prev_chr_is_eol)
+                break;
+            prev_chr_is_eol = (c == '\n');
+        } else
+            prev_chr_is_eol = 0;
+        if (c != '\r')
+            av_bprint_chars(buf, c, 1);
+    }
+    av_bprint_chars(buf, '\0', 1);
+    return pos;
+}
+
+static int webvtt_read_header(AVFormatContext *s)
+{
+    WebVTTContext *webvtt = s->priv_data;
+    AVBPrint header, cue;
+    int res = 0;
+    AVStream *st = avformat_new_stream(s, NULL);
+
+    if (!st)
+        return AVERROR(ENOMEM);
+    avpriv_set_pts_info(st, 64, 1, 1000);
+    st->codec->codec_type = AVMEDIA_TYPE_SUBTITLE;
+    st->codec->codec_id   = AV_CODEC_ID_WEBVTT;
+
+    av_bprint_init(&header, 0, AV_BPRINT_SIZE_UNLIMITED);
+    av_bprint_init(&cue,    0, AV_BPRINT_SIZE_UNLIMITED);
+
+    for (;;) {
+        int i, len;
+        int64_t pos = extract_cue(&cue, s->pb);
+        AVPacket *sub;
+        const char *p = cue.str;
+        const char *identifier = p;
+        //const char *settings = NULL;
+        int64_t ts_start, ts_end;
+
+        if (!*p) // EOF
+            break;
+
+        /* ignore header chunk */
+        if (!strncmp(p, "\xEF\xBB\xBFWEBVTT", 9) ||
+            !strncmp(p, "WEBVTT", 6))
+            continue;
+
+        /* optional cue identifier (can be a number like in SRT or some kind of
+         * chaptering id), silently skip it */
+        for (i = 0; p[i] && p[i] != '\n'; i++) {
+            if (!strncmp(p + i, "-->", 3)) {
+                identifier = NULL;
+                break;
+            }
+        }
+        if (identifier)
+            p += strcspn(p, "\n");
+
+        /* cue timestamps */
+        if ((ts_start = read_ts(p)) == AV_NOPTS_VALUE)
+            break;
+        if (!(p = strstr(p, "-->")))
+            break;
+        p += 3;
+        do p++; while (*p == ' ' || *p == '\t');
+        if ((ts_end = read_ts(p)) == AV_NOPTS_VALUE)
+            break;
+
+        /* optional cue settings, TODO: store in side_data */
+        p += strcspn(p, "\n\t ");
+        while (*p == '\t' || *p == ' ')
+            p++;
+        if (*p != '\n') {
+            //settings = p;
+            p += strcspn(p, "\n");
+        }
+        if (*p == '\n')
+            p++;
+
+        /* create packet */
+        len = cue.str + cue.len - p - 1;
+        sub = ff_subtitles_queue_insert(&webvtt->q, p, len, 0);
+        if (!sub) {
+            res = AVERROR(ENOMEM);
+            goto end;
+        }
+        sub->pos = pos;
+        sub->pts = ts_start;
+        sub->duration = ts_end - ts_start;
+    }
+
+    ff_subtitles_queue_finalize(&webvtt->q);
+
+end:
+    av_bprint_finalize(&cue,    NULL);
+    av_bprint_finalize(&header, NULL);
+    return res;
+}
+
+static int webvtt_read_packet(AVFormatContext *s, AVPacket *pkt)
+{
+    WebVTTContext *webvtt = s->priv_data;
+    return ff_subtitles_queue_read_packet(&webvtt->q, pkt);
+}
+
+static int webvtt_read_close(AVFormatContext *s)
+{
+    WebVTTContext *webvtt = s->priv_data;
+    ff_subtitles_queue_clean(&webvtt->q);
+    return 0;
+}
+
+AVInputFormat ff_webvtt_demuxer = {
+    .name           = "webvtt",
+    .long_name      = NULL_IF_CONFIG_SMALL("WebVTT subtitle"),
+    .priv_data_size = sizeof(WebVTTContext),
+    .read_probe     = webvtt_probe,
+    .read_header    = webvtt_read_header,
+    .read_packet    = webvtt_read_packet,
+    .read_close     = webvtt_read_close,
+    .flags          = AVFMT_GENERIC_INDEX,
+    .extensions     = "vtt",
+};