[FFmpeg-devel] [PATCH] dvbsub fix transcoding
Michael Niedermayer
michaelni at gmx.at
Thu Jun 5 01:42:52 CEST 2014
On Thu, Jun 05, 2014 at 12:33:37AM +0530, Anshul wrote:
> On June 4, 2014 10:56:02 PM IST, Michael Niedermayer <michaelni at gmx.at> wrote:
> >On Wed, Jun 04, 2014 at 10:44:25PM +0530, Anshul wrote:
> >> On June 4, 2014 9:12:13 PM IST, Michael Niedermayer
> ><michaelni at gmx.at> wrote:
> >> >On Sun, Jun 01, 2014 at 10:44:48PM +0530, Anshul Maheshwari wrote:
> >> >> On Fri, May 23, 2014 at 3:50 PM, anshul <anshul.ffmpeg at gmail.com>
> >> >wrote:
> >> >> > On 05/22/2014 06:43 PM, Wim Vander Schelden wrote:
> >> >> >>
> >> >> >> On Thu, May 22, 2014 at 3:01 PM, Wim Vander Schelden
> >> >> >> <lists at fixnum.org>wrote:
> >> >> >>
> >> >> >>> These subtitles not disappearing is exactly the issue that's
> >> >introduced
> >> >> >>> by
> >> >> >>> sending the second (empty, "clearing") packet (by removing the
> >nb
> >> >= 2).
> >> >> >
> >> >> > you mean not sending second packet here.
> >> >> >>>
> >> >> >>> Note that you are now relying on the DVB subtitle timeout
> >value,
> >> >which
> >> >> is
> >> >> >>>
> >> >> >>> only for "safety" purposes (ie, the encoder crashed), and is
> >only
> >> >> >>> required
> >> >> >>> by the specification to be followed with a 5 second accuracy
> >(so
> >> >it is
> >> >> >>> completely useless for functioning subtitles)!
> >> >> >>>
> >> >> > agree its for safety purpose, but as you see -0/+5 accuracy
> >means
> >> >that it
> >> >> > might be possible that subtitle
> >> >> > are on screen +5 second ie more then required time. so using
> >> >timeout does
> >> >> > not have any harm.
> >> >> > though relying only on it, is harmful.
> >> >> > following is copy pasted from ETSI EN 300 743 V1.3.1 (2006-11)
> >> >> > page_time_out: The period, expressed in seconds, after which a
> >page
> >> >> instance
> >> >> > is no longer valid and consequently shall
> >> >> > be erased from the screen, should it not have been redefined
> >before
> >> >that.
> >> >> > The time-out period starts when the page
> >> >> > instance is first displayed. The page_time_out value applies to
> >> >each page
> >> >> > instance until its value is redefined. The
> >> >> > purpose of the time-out period is to avoid a page instance
> >> >remaining on
> >> >> the
> >> >> > screen "for ever" if the IRD happens to have
> >> >> > missed the redefinition or deletion of the page instance. The
> >> >time-out
> >> >> > period does not need to be counted very
> >> >> > accurately by the IRD: a reaction accuracy of -0/+5 s is
> >accurate
> >> >enough.
> >> >> >
> >> >> >> I seem to have misformulated my ordering issue in my earlier
> >mail:
> >> >the
> >> >> >> problem occurs when subtitle X only disappears after subtitle
> >X+1
> >> >should
> >> >> >> start being displayed, as the "clear" packet for X is emitted
> >> >immediately
> >> >> >> after the "show" packet for X, so before the "show" packet for
> >> >X+1.
> >> >> >>
> >> >> > yes agree :)
> >> >> >
> >> >> >
> >> >> > So problem is
> >> >> > end_display_time is not reliable in case of dvbsub decoder,
> >> >> > since end_display_time in dvbsub decoder is calculated using
> >> >> page_time_out.
> >> >> > which is only for safety purpose.
> >> >> >
> >> >> > I am trying to fix end_display_time in dvbsub decoder.
> >> >> > I want to know should i cache the subtitle till i get
> >clear_display
> >> >> > region/overlap region
> >> >> > or should i try to overwrite end_display_time when i have
> >recieved
> >> >some
> >> >> new
> >> >> > region.
> >> >> >
> >> >> > just now i have attached patch which stop second loop only when
> >> >stream was
> >> >> > decoded by
> >> >> > dvbsubtile.
> >> >> >
> >> >> > -Anshul
> >> >>
> >> >> Hi
> >> >>
> >> >> I have attached new patch which fix end_display_time in subtitle.
> >> >>
> >> >> > 7.2.6
> >> >> > End of display set segment
> >> >> > The end_of_display_set_segment provides an explicit indication
> >to
> >> >the
> >> >> decoder that transmission of a display set is
> >> >> > complete. The end_of_display_set_segment shall be inserted into
> >the
> >> >> stream immediately after the last
> >> >> > object_data_segment for each display set. It shall be present
> >for
> >> >each
> >> >> subtitle service in a subtitle stream,
> >> >> *although> decoders need not take advantage of this segment* and
> >may
> >> >apply
> >> >> other strategies to determine when they have sufficient
> >> >> > information from a display set to commence decoding.
> >> >> As spec say not to use end of display segment for any purpose. I
> >> >removed
> >> >> use of eod segment
> >> >>
> >> >> Thanks
> >> >> Anshul
> >> >
> >> >> dvbsubdec.c | 162
> >> >+++++++++++++++++++++++++++++-------------------------------
> >> >> 1 file changed, 79 insertions(+), 83 deletions(-)
> >> >> d7dc4775cac095f0f31a4879e763fd1dba365605
> >> >0001-fix-transcoding-dvbsub-to-dvbsub.patch
> >> >> From 35f48dd9d8929989b2ca130f72c66cef9a2f3a95 Mon Sep 17 00:00:00
> >> >2001
> >> >> From: Anshul Maheshwari <anshul.ffmpeg at gmail.com>
> >> >> Date: Sun, 1 Jun 2014 22:37:28 +0530
> >> >> Subject: [PATCH] fix transcoding dvbsub to dvbsub
> >> >>
> >> >> fix ticket #2024
> >> >> ---
> >> >> libavcodec/dvbsubdec.c | 162
> >> >++++++++++++++++++++++++-------------------------
> >> >> 1 file changed, 79 insertions(+), 83 deletions(-)
> >> >>
> >> >> diff --git a/libavcodec/dvbsubdec.c b/libavcodec/dvbsubdec.c
> >> >> index 9d74b1a..76ed389 100644
> >> >> --- a/libavcodec/dvbsubdec.c
> >> >> +++ b/libavcodec/dvbsubdec.c
> >> >> @@ -232,6 +232,7 @@ typedef struct DVBSubContext {
> >> >>
> >> >> int version;
> >> >> int time_out;
> >> >> + int64_t prev_start;
> >> >> DVBSubRegion *region_list;
> >> >> DVBSubCLUT *clut_list;
> >> >> DVBSubObject *object_list;
> >> >> @@ -1148,11 +1149,18 @@ static void
> >> >dvbsub_parse_region_segment(AVCodecContext *avctx,
> >> >> }
> >> >>
> >> >> static void dvbsub_parse_page_segment(AVCodecContext *avctx,
> >> >> - const uint8_t *buf, int
> >> >buf_size)
> >> >> + const uint8_t *buf, int
> >> >buf_size, AVSubtitle *sub)
> >> >> {
> >> >> DVBSubContext *ctx = avctx->priv_data;
> >> >> DVBSubRegionDisplay *display;
> >> >> DVBSubRegionDisplay *tmp_display_list, **tmp_ptr;
> >> >> + DVBSubDisplayDefinition *display_def =
> >ctx->display_definition;
> >> >> + DVBSubRegion *region;
> >> >> + AVSubtitleRect *rect;
> >> >> + DVBSubCLUT *clut;
> >> >> + uint32_t *clut_table;
> >> >> + int i;
> >> >> + int offset_x=0, offset_y=0;
> >> >>
> >> >> const uint8_t *buf_end = buf + buf_size;
> >> >> int region_id;
> >> >> @@ -1167,12 +1175,80 @@ static void
> >> >dvbsub_parse_page_segment(AVCodecContext *avctx,
> >> >> version = ((*buf)>>4) & 15;
> >> >> page_state = ((*buf++) >> 2) & 3;
> >> >>
> >> >> - if (ctx->version != version) {
> >> >> + if (ctx->version == version) {
> >> >> + return;
> >> >> + }
> >> >>
> >> >> ctx->time_out = timeout;
> >> >> ctx->version = version;
> >> >>
> >> >> av_dlog(avctx, "Page time out %ds, state %d\n",
> >ctx->time_out,
> >> >page_state);
> >> >> + if (display_def) {
> >> >> + offset_x = display_def->x;
> >> >> + offset_y = display_def->y;
> >> >> + }
> >> >> + sub->num_rects = 0;
> >> >> + for (display = ctx->display_list; display; display =
> >> >display->next) {
> >> >> + region = get_region(ctx, display->region_id);
> >> >> + if (region && region->dirty)
> >> >> + sub->num_rects++;
> >> >> + }
> >> >> +
> >> >> + if (sub->num_rects > 0) {
> >> >> + if(ctx->prev_start)
> >> >> + sub->end_display_time = av_rescale_q((sub->pts -
> >> >ctx->prev_start )/90, AV_TIME_BASE_Q, avctx->time_base) - 1;
> >> >
> >> >this delays the subtitle packets, they do have correct timestamps
> >maybe
> >> >but each subtitle will be output only when the next subtitle becomes
> >> >available, which would require a player to buffer several seconds
> >> >of video to be able to combine subtitles and video.
> >> >
> >
> >> If I got u correct then,
> >> We need to check whether this subtitle is going to be encoded or not
> >and set avoption for this.
> >
> >yes thats a possibility
> >
> >
> >> This would be special case for dvb and add ugly hack like in
> >encode_subtitle.
> >
> >yes, or it could be moved elsewhere, iam not sure which is the best
> >place. But its a ugly hack no matter where its done
> >If dvb is the only that needs this then it could be done inside the
> >dvb decoder
> >
> >
> If it could be done inside dvb decoder it would be best, I dont find any parameter which tells which encoder is used in decoder.
>
> I dont know where we use AVIO_FLAG_NONBLOCK . in this situation this flag suits my need.
> Should I go with this flag?
that flag is from avformat and doesnt seem to fit semantically
something like
need_subtitle_duration / compute_subtitle_duration / whatever
as a codec private AVOption
seems the obvious choice
[...]
--
Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
No great genius has ever existed without some touch of madness. -- Aristotle
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