[FFmpeg-devel] [PATCH] Respect `append_list` flag in subtitle playlists

[Jonathan Baecker]

Ensure that when the `-hls_flags append_list` option is set, that *.vtt files in stream_vtt.m3u8 are correctly updated. This fixes https://trac.ffmpeg.org/ticket/11208

This is a bit of an ugly fix, let me know what you think.
---
 libavformat/hlsenc.c | 37 +++++++++++++++++++++++++++++++++++++
 1 file changed, 37 insertions(+)

diff --git a/libavformat/hlsenc.c b/libavformat/hlsenc.c
index 1e932b7..e93af4c 100644
--- a/libavformat/hlsenc.c
+++ b/libavformat/hlsenc.c
@@ -1202,6 +1202,22 @@ static int hls_append_segment(struct AVFormatContext *s, HLSContext *hls,
     return 0;
 }
 
+static int extract_number(const char *filename) {
+    const char *dot = strrchr(filename, '.');
+    const char *num_start = dot - 1;
+
+    while (num_start > filename && *num_start >= '0' && *num_start <= '9') {
+        num_start--;
+    }
+
+    num_start++;
+
+    if (num_start == dot)
+        return -1;
+
+    return atoi(num_start);
+}
+
 static int parse_playlist(AVFormatContext *s, const char *url, VariantStream *vs)
 {
     HLSContext *hls = s->priv_data;
@@ -1294,6 +1310,27 @@ static int parse_playlist(AVFormatContext *s, const char *url, VariantStream *vs
                     ret = AVERROR(ENOMEM);
                     goto fail;
                 }
+                if (vs->has_subtitle) {
+                    int vtt_index = extract_number(line);
+                    char *vtt_file = av_asprintf(av_basename(vs->vtt_basename), vtt_index);
+                    char *new_vtt;
+
+                    if (!vtt_file) {
+                        ret = AVERROR(ENOMEM);
+                        goto fail;
+                    }
+
+                    new_vtt = av_strdup(vtt_file);
+                    av_free(vtt_file);
+
+                    if (!new_vtt) {
+                        ret = AVERROR(ENOMEM);
+                        goto fail;
+                    }
+
+                    ff_format_set_url(vs->vtt_avf, new_vtt);
+                }
+
                 ff_format_set_url(vs->avf, new_file);
                 is_segment = 0;
                 new_start_pos = avio_tell(vs->avf->pb);
-- 
2.46.1