[FFmpeg-devel] [PATCH] microdvd: sanitize AVPackets.

[Clément Bœsch]

Current MicroDVD AVPackets contain timing information and trailing line
breaks. The data is now only composed of the markup data. Doing this
consistently between text subtitles decoders allows to use different
codec for various formats. For instance, MicroDVD markup is sometimes
found in some VPlayer files. Also, generally speaking, the subtitles
text decoder also have no use of these timing (and they must not use
them since it would break any user timing adjustment).

Technically, this is a major ABI break. In practice, a mismatching
lavf/lavc will now error out for MicroDVD encoding. Supporting both
formats requires unnecessary complex and fragile code.

FATE needs update because line breaks in the ASS file were "\n" (because
that's what is used in the original file). ASS format expect "\r\n" line
breaks; this commit fixes this issue. Also note that this "\r\n"
trailing need to be moved at some point from the decoders to the ASS
muxer.

TODO: bump lavf & lavc minor
---
 libavcodec/microdvddec.c    | 19 ++++++++++++++-----
 libavformat/microdvddec.c   | 12 +++++++++---
 tests/ref/fate/sub-microdvd |  2 +-
 3 files changed, 24 insertions(+), 9 deletions(-)

diff --git a/libavcodec/microdvddec.c b/libavcodec/microdvddec.c
index e08cc31..6a91015 100644
--- a/libavcodec/microdvddec.c
+++ b/libavcodec/microdvddec.c
@@ -260,6 +260,7 @@ static int microdvd_decode_frame(AVCodecContext *avctx,
 {
     AVSubtitle *sub = data;
     AVBPrint new_line;
+    char c;
     char *decoded_sub;
     char *line = avpkt->data;
     char *end = avpkt->data + avpkt->size;
@@ -268,11 +269,17 @@ static int microdvd_decode_frame(AVCodecContext *avctx,
     if (avpkt->size <= 0)
         return avpkt->size;
 
-    av_bprint_init(&new_line, 0, 2048);
+    /* To be removed later */
+    if ((sscanf(line, "{%*d}{}%c",    &c) == 1 ||
+         sscanf(line, "{%*d}{%*d}%c", &c) == 1) &&
+        line[avpkt->size - 1] == '\n') {
+        av_log(avctx, AV_LOG_WARNING, "AVPacket is not clean (contains timing "
+               "information and a trailing line break). You need to upgrade "
+               "your libavformat or sanitize your packet.\n");
+        return AVERROR_INVALIDDATA;
+    }
 
-    // skip {frame_start}{frame_end}
-    line = strchr(line, '}'); if (!line) goto end; line++;
-    line = strchr(line, '}'); if (!line) goto end; line++;
+    av_bprint_init(&new_line, 0, 2048);
 
     // subtitle content
     while (line < end && *line) {
@@ -294,8 +301,9 @@ static int microdvd_decode_frame(AVCodecContext *avctx,
             line++;
         }
     }
+    if (new_line.len) {
+        av_bprintf(&new_line, "\r\n");
 
-end:
     av_bprint_finalize(&new_line, &decoded_sub);
     if (*decoded_sub) {
         int64_t start    = avpkt->pts;
@@ -306,6 +314,7 @@ end:
         ff_ass_add_rect(sub, decoded_sub, ts_start, ts_duration, 0);
     }
     av_free(decoded_sub);
+    }
 
     *got_sub_ptr = sub->num_rects > 0;
     return avpkt->size;
diff --git a/libavformat/microdvddec.c b/libavformat/microdvddec.c
index 5d5b83f..7067de7 100644
--- a/libavformat/microdvddec.c
+++ b/libavformat/microdvddec.c
@@ -83,12 +83,14 @@ static int microdvd_read_header(AVFormatContext *s)
         return AVERROR(ENOMEM);
 
     while (!url_feof(s->pb)) {
+        char *p = line;
         AVPacket *sub;
         int64_t pos = avio_tell(s->pb);
         int len = ff_get_line(s->pb, line, sizeof(line));
 
         if (!len)
             break;
+        line[strcspn(line, "\r\n")] = 0;
         if (i < 3) {
             int frame;
             double fps;
@@ -107,12 +109,16 @@ static int microdvd_read_header(AVFormatContext *s)
                 continue;
             }
         }
-        sub = ff_subtitles_queue_insert(&microdvd->q, line, len, 0);
+        p = strchr(p, '}'); if (!p) continue; p++;
+        p = strchr(p, '}'); if (!p) continue; p++;
+        if (!*p)
+            continue;
+        sub = ff_subtitles_queue_insert(&microdvd->q, p, strlen(p), 0);
         if (!sub)
             return AVERROR(ENOMEM);
         sub->pos = pos;
-        sub->pts = get_pts(sub->data);
-        sub->duration = get_duration(sub->data);
+        sub->pts = get_pts(line);
+        sub->duration = get_duration(line);
     }
     ff_subtitles_queue_finalize(&microdvd->q);
     avpriv_set_pts_info(st, 64, pts_info.den, pts_info.num);
diff --git a/tests/ref/fate/sub-microdvd b/tests/ref/fate/sub-microdvd
index 9fc10fb..2059989 100644
--- a/tests/ref/fate/sub-microdvd
+++ b/tests/ref/fate/sub-microdvd
@@ -1 +1 @@
-6356b8c53169aae6a20bce34d0f7be87
+35e133576aa3881d2de8dbf39a8d6df7
-- 
1.8.0.3