2017.02.03. 0:27 keltezéssel, Aman Gupta írta:
On Wed, Feb 1, 2017 at 6:03 AM, Bodecs Bela <bode...@vivanet.hu> wrote:


2017.01.31. 21:29 keltezéssel, Aman Gupta írta:

From: Aman Gupta <a...@tmm1.net>

Adds a `-hls_flags +temp_file` which will write segment data to
filename.tmp, and then rename to filename when the segment is complete
and before the file is added to the m3u8 playlist.

This patch is similar in spirit to one used in Plex's ffmpeg fork, and
allows a transcoding webserver to ensure incomplete segment files are
never served up accidentally.
---
   libavformat/hlsenc.c | 15 +++++++++++++++
   1 file changed, 15 insertions(+)

diff --git a/libavformat/hlsenc.c b/libavformat/hlsenc.c
index bd1e684..23b9011 100644
--- a/libavformat/hlsenc.c
+++ b/libavformat/hlsenc.c
@@ -76,6 +76,7 @@ typedef enum HLSFlags {
       HLS_SECOND_LEVEL_SEGMENT_INDEX = (1 << 8), // include segment index
in segment filenames when use_localtime  e.g.: %%03d
       HLS_SECOND_LEVEL_SEGMENT_DURATION = (1 << 9), // include segment
duration (microsec) in segment filenames when use_localtime  e.g.: %%09t
       HLS_SECOND_LEVEL_SEGMENT_SIZE = (1 << 10), // include segment size
(bytes) in segment filenames when use_localtime  e.g.: %%014s
+    HLS_TEMP_FILE = (1 << 11),
   } HLSFlags;
     typedef enum {
@@ -915,6 +916,10 @@ static int hls_start(AVFormatContext *s)
         set_http_options(&options, c);
   +    if (c->flags & HLS_TEMP_FILE) {
+        av_strlcat(oc->filename, ".tmp", sizeof(oc->filename));
+    }
+
       if (c->key_info_file) {
           if ((err = hls_encryption_start(s)) < 0)
               goto fail;
@@ -1276,6 +1281,15 @@ static int hls_write_packet(AVFormatContext *s,
AVPacket *pkt)
             av_write_frame(oc, NULL); /* Flush any buffered data */
   +        if (hls->flags & HLS_TEMP_FILE) {
+            size_t len = strlen(oc->filename);
+            char final_filename[sizeof(oc->filename)];
+            av_strlcpy(final_filename, oc->filename, len);
+            final_filename[len-4] = '\0';
+            ff_rename(oc->filename, final_filename, s);
+            oc->filename[len-4] = '\0';
+        }
+
           new_start_pos = avio_tell(hls->avf->pb);
           hls->size = new_start_pos - hls->start_pos;
           ret = hls_append_segment(s, hls, hls->duration, hls->start_pos,
hls->size);
@@ -1406,6 +1420,7 @@ static const AVOption options[] = {
       {"hls_subtitle_path",     "set path of hls subtitles",
OFFSET(subtitle_filename), AV_OPT_TYPE_STRING, {.str = NULL},  0, 0,    E},
       {"hls_flags",     "set flags affecting HLS playlist and media file
generation", OFFSET(flags), AV_OPT_TYPE_FLAGS, {.i64 = 0 }, 0, UINT_MAX, E,
"flags"},
       {"single_file",   "generate a single media file indexed with byte
ranges", 0, AV_OPT_TYPE_CONST, {.i64 = HLS_SINGLE_FILE }, 0, UINT_MAX,   E,
"flags"},
+    {"temp_file", "write segment to temporary file and rename when
complete", 0, AV_OPT_TYPE_CONST, {.i64 = HLS_TEMP_FILE }, 0, UINT_MAX,   E,
"flags"},
       {"delete_segments", "delete segment files that are no longer part
of the playlist", 0, AV_OPT_TYPE_CONST, {.i64 = HLS_DELETE_SEGMENTS }, 0,
UINT_MAX,   E, "flags"},
       {"round_durations", "round durations in m3u8 to whole numbers", 0,
AV_OPT_TYPE_CONST, {.i64 = HLS_ROUND_DURATIONS }, 0, UINT_MAX,   E,
"flags"},
       {"discont_start", "start the playlist with a discontinuity tag", 0,
AV_OPT_TYPE_CONST, {.i64 = HLS_DISCONT_START }, 0, UINT_MAX,   E, "flags"},

I think the phrase  in your email subject "to create atomically"
misleading because another renaming may occur afterwards your temp renaming
if second_level_segment_size or second_level_segment_duration flag is on.
But the idea to write segment content into a temp file is good by me. To
ensure the amoticity the two distinct renamings may be merged.

I agree my use of "atomic" is confusing. I removed this from the commit
message in v2 of the patch.


I have never thought of it but after your idea I concluded  that the
segment file names are predictable.
In live streaming enviroment somebody predicting the segment name may see
the program some seconds earlier than any other viewer by downloading the
unpublished segment. (with one segment duration seconds earlier)
If the temp file name would be random name, then your idea may be seen as
a security feature.
What is your opinion about this possibility?

I don't have a strong opinion on this. Presumably if someone is concerned
about this, they can still use my temp_file patch and configure their web
server to reject any requests for *.tmp

Yes, I agree with you. Maybe You can put a short notice about this into the documentation.

bb

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