[FFmpeg-devel] [PATCH v3 2/2] avformat/movenc: add support for TTML muxing

Andreas Rheinhardt andreas.rheinhardt at outlook.com
Thu Aug 5 22:32:52 EEST 2021


Jan Ekström:
> From: Jan Ekström <jan.ekstrom at 24i.com>
> 
> Includes basic support for both the ISMV ('dfxp') and MP4 ('stpp')
> methods. This initial version also foregoes fragmentation support
> in case the built-in sample squashing is to be utilized, as this
> eases the initial review.
> 
> Additionally, add basic tests for both muxing modes in MP4.
> 
> Signed-off-by: Jan Ekström <jan.ekstrom at 24i.com>
> ---
>  libavformat/Makefile             |   2 +-
>  libavformat/isom.h               |   3 +
>  libavformat/movenc.c             | 179 ++++++++++++++++++++++++++++++-
>  libavformat/movenc.h             |   5 +
>  libavformat/movenc_ttml.c        | 178 ++++++++++++++++++++++++++++++
>  libavformat/movenc_ttml.h        |  31 ++++++
>  tests/fate/subtitles.mak         |   4 +
>  tests/ref/fate/sub-ttml-mp4-dfxp |  44 ++++++++
>  tests/ref/fate/sub-ttml-mp4-stpp |  44 ++++++++
>  9 files changed, 487 insertions(+), 3 deletions(-)
>  create mode 100644 libavformat/movenc_ttml.c
>  create mode 100644 libavformat/movenc_ttml.h
>  create mode 100644 tests/ref/fate/sub-ttml-mp4-dfxp
>  create mode 100644 tests/ref/fate/sub-ttml-mp4-stpp
> 
> diff --git a/libavformat/Makefile b/libavformat/Makefile
> index 813ddd3c20..7e0f587b41 100644
> --- a/libavformat/Makefile
> +++ b/libavformat/Makefile
> @@ -337,7 +337,7 @@ OBJS-$(CONFIG_MOV_DEMUXER)               += mov.o mov_chan.o mov_esds.o \
>                                              qtpalette.o replaygain.o
>  OBJS-$(CONFIG_MOV_MUXER)                 += movenc.o av1.o avc.o hevc.o vpcc.o \
>                                              movenchint.o mov_chan.o rtp.o \
> -                                            movenccenc.o rawutils.o
> +                                            movenccenc.o movenc_ttml.o rawutils.o
>  OBJS-$(CONFIG_MP2_MUXER)                 += rawenc.o
>  OBJS-$(CONFIG_MP3_DEMUXER)               += mp3dec.o replaygain.o
>  OBJS-$(CONFIG_MP3_MUXER)                 += mp3enc.o rawenc.o id3v2enc.o
> diff --git a/libavformat/isom.h b/libavformat/isom.h
> index ac1b3f3d56..34a58c79b7 100644
> --- a/libavformat/isom.h
> +++ b/libavformat/isom.h
> @@ -387,4 +387,7 @@ static inline enum AVCodecID ff_mov_get_lpcm_codec_id(int bps, int flags)
>      return ff_get_pcm_codec_id(bps, flags & 1, flags & 2, flags & 4 ? -1 : 0);
>  }
>  
> +#define MOV_ISMV_TTML_TAG MKTAG('d', 'f', 'x', 'p')
> +#define MOV_MP4_TTML_TAG  MKTAG('s', 't', 'p', 'p')
> +
>  #endif /* AVFORMAT_ISOM_H */
> diff --git a/libavformat/movenc.c b/libavformat/movenc.c
> index c85efe8748..f3e295ad80 100644
> --- a/libavformat/movenc.c
> +++ b/libavformat/movenc.c
> @@ -56,6 +56,8 @@
>  #include "hevc.h"
>  #include "rtpenc.h"
>  #include "mov_chan.h"
> +#include "movenc_ttml.h"
> +#include "ttmlenc.h"
>  #include "vpcc.h"
>  
>  static const AVOption options[] = {
> @@ -119,6 +121,7 @@ static const AVClass mov_isobmff_muxer_class = {
>  };
>  
>  static int get_moov_size(AVFormatContext *s);
> +static int mov_write_single_packet(AVFormatContext *s, AVPacket *pkt);
>  
>  static int utf8len(const uint8_t *b)
>  {
> @@ -1787,7 +1790,29 @@ static int mov_write_subtitle_tag(AVIOContext *pb, MOVTrack *track)
>  
>      if (track->par->codec_id == AV_CODEC_ID_DVD_SUBTITLE)
>          mov_write_esds_tag(pb, track);
> -    else if (track->par->extradata_size)
> +    else if (track->par->codec_id == AV_CODEC_ID_TTML) {
> +        switch (track->par->codec_tag) {
> +        case MOV_ISMV_TTML_TAG:
> +            // ISMV dfxp requires no extradata.
> +            break;
> +        case MOV_MP4_TTML_TAG:
> +            // As specified in 14496-30, XMLSubtitleSampleEntry
> +            // Namespace
> +            avio_put_str(pb, "http://www.w3.org/ns/ttml");
> +            // Empty schema_location
> +            avio_w8(pb, 0);
> +            // Empty auxiliary_mime_types
> +            avio_w8(pb, 0);
> +            break;
> +        default:
> +            av_log(NULL, AV_LOG_ERROR,
> +                   "Unknown codec tag '%s' utilized for TTML stream with "
> +                   "index %d (track id %d)!\n",
> +                   av_fourcc2str(track->par->codec_tag), track->st->index,
> +                   track->track_id);
> +            return AVERROR(EINVAL);
> +        }
> +    } else if (track->par->extradata_size)
>          avio_write(pb, track->par->extradata, track->par->extradata_size);
>  
>      if (track->mode == MODE_MP4 &&
> @@ -2661,6 +2686,14 @@ static int mov_write_nmhd_tag(AVIOContext *pb)
>      return 12;
>  }
>  
> +static int mov_write_sthd_tag(AVIOContext *pb)
> +{
> +    avio_wb32(pb, 12);
> +    ffio_wfourcc(pb, "sthd");
> +    avio_wb32(pb, 0);
> +    return 12;
> +}
> +
>  static int mov_write_tcmi_tag(AVIOContext *pb, MOVTrack *track)
>  {
>      int64_t pos = avio_tell(pb);
> @@ -2787,6 +2820,8 @@ static int mov_write_hdlr_tag(AVFormatContext *s, AVIOContext *pb, MOVTrack *tra
>                      hdlr_type = "sbtl";
>                  } else if (track->tag == MKTAG('m','p','4','s')) {
>                      hdlr_type = "subp";
> +                } else if (track->tag == MOV_MP4_TTML_TAG) {
> +                    hdlr_type = "subt";
>                  } else {
>                      hdlr_type = "text";
>                  }
> @@ -2865,6 +2900,8 @@ static int mov_write_minf_tag(AVFormatContext *s, AVIOContext *pb, MOVMuxContext
>      else if (track->par->codec_type == AVMEDIA_TYPE_SUBTITLE) {
>          if (track->tag == MKTAG('t','e','x','t') || is_clcp_track(track)) {
>              mov_write_gmhd_tag(pb, track);
> +        } else if (track->tag == MOV_MP4_TTML_TAG) {
> +            mov_write_sthd_tag(pb);
>          } else {
>              mov_write_nmhd_tag(pb);
>          }
> @@ -5253,6 +5290,68 @@ static int mov_flush_fragment_interleaving(AVFormatContext *s, MOVTrack *track)
>      return 0;
>  }
>  
> +static int mov_write_squashed_packet(AVFormatContext *s, MOVTrack *track)
> +{
> +    MOVMuxContext *mov = s->priv_data;
> +    AVPacket *squashed_packet = mov->pkt;
> +    int ret = AVERROR_BUG;
> +
> +    switch (track->st->codecpar->codec_id) {
> +    case AV_CODEC_ID_TTML: {
> +        int had_packets = !!track->squashed_packet_queue;
> +
> +        if ((ret = ff_mov_generate_squashed_ttml_packet(s, track, squashed_packet)) < 0) {
> +            goto finish_squash;
> +        }
> +
> +        // We have generated a padding packet (no actual input packets in
> +        // queue) and its duration is zero. Skipping writing it.
> +        if (!had_packets && squashed_packet->duration == 0) {
> +            goto finish_squash;
> +        }
> +
> +        track->end_reliable = 1;
> +        break;
> +    }
> +    default:
> +        ret = AVERROR(EINVAL);
> +        goto finish_squash;
> +    }
> +
> +    squashed_packet->stream_index = track->st->index;
> +
> +    ret = mov_write_single_packet(s, squashed_packet);
> +
> +finish_squash:
> +    av_packet_unref(squashed_packet);
> +
> +    return ret;
> +}
> +
> +static int mov_write_squashed_packets(AVFormatContext *s)
> +{
> +    MOVMuxContext *mov = s->priv_data;
> +
> +    for (int i = 0; i < s->nb_streams; i++) {
> +        MOVTrack *track = &mov->tracks[i];
> +        int ret = AVERROR_BUG;
> +
> +        if (track->squash_fragment_samples_to_one && !track->entry) {
> +            if ((ret = mov_write_squashed_packet(s, track)) < 0) {
> +                av_log(s, AV_LOG_ERROR,
> +                       "Failed to write squashed packet for %s stream with "
> +                       "index %d and track id %d. Error: %s\n",
> +                       avcodec_get_name(track->st->codecpar->codec_id),
> +                       track->st->index, track->track_id,
> +                       av_err2str(ret));
> +                return ret;
> +            }
> +        }
> +    }
> +
> +    return 0;
> +}
> +
>  static int mov_flush_fragment(AVFormatContext *s, int force)
>  {
>      MOVMuxContext *mov = s->priv_data;
> @@ -5264,6 +5363,11 @@ static int mov_flush_fragment(AVFormatContext *s, int force)
>      if (!(mov->flags & FF_MOV_FLAG_FRAGMENT))
>          return 0;
>  
> +    // Check if we have any tracks that require squashing.
> +    // In that case, we'll have to write the packet here.
> +    if ((ret = mov_write_squashed_packets(s)) < 0)
> +        return ret;
> +
>      // Try to fill in the duration of the last packet in each stream
>      // from queued packets in the interleave queues. If the flushing
>      // of fragments was triggered automatically by an AVPacket, we
> @@ -5739,7 +5843,8 @@ int ff_mov_write_packet(AVFormatContext *s, AVPacket *pkt)
>      trk->cluster[trk->entry].entries          = samples_in_chunk;
>      trk->cluster[trk->entry].dts              = pkt->dts;
>      trk->cluster[trk->entry].pts              = pkt->pts;
> -    if (!trk->entry && trk->start_dts != AV_NOPTS_VALUE) {
> +    if (!trk->squash_fragment_samples_to_one &&
> +        !trk->entry && trk->start_dts != AV_NOPTS_VALUE) {
>          if (!trk->frag_discont) {
>              /* First packet of a new fragment. We already wrote the duration
>               * of the last packet of the previous fragment based on track_duration,
> @@ -6032,6 +6137,33 @@ static int mov_write_packet(AVFormatContext *s, AVPacket *pkt)
>              }
>          }
>  
> +        if (trk->squash_fragment_samples_to_one) {
> +            /*
> +             * If the track has to have its samples squashed into one sample,
> +             * we just take it into the track's queue.
> +             * This will then be utilized as the samples get written in either
> +             * mov_flush_fragment or when the mux is finalized in
> +             * mov_write_trailer.
> +             */
> +            int ret = AVERROR_BUG;
> +
> +            if (pkt->pts == AV_NOPTS_VALUE) {
> +                av_log(s, AV_LOG_ERROR,
> +                       "Packets without a valid presentation timestamp are "
> +                       "not supported with packet squashing!\n");
> +                return AVERROR(EINVAL);
> +            }
> +
> +            if ((ret = avpriv_packet_list_put(&trk->squashed_packet_queue,
> +                                              &trk->squashed_packet_queue_end,
> +                                              pkt, av_packet_ref, 0)) < 0) {
> +                return ret;
> +            }
> +
> +            return 0;
> +        }
> +
> +
>          if (trk->mode == MODE_MOV && trk->par->codec_type == AVMEDIA_TYPE_VIDEO) {
>              AVPacket *opkt = pkt;
>              int reshuffle_ret, ret;
> @@ -6310,6 +6442,11 @@ static void mov_free(AVFormatContext *s)
>  
>          ff_mov_cenc_free(&mov->tracks[i].cenc);
>          ffio_free_dyn_buf(&mov->tracks[i].mdat_buf);
> +
> +        if (mov->tracks[i].squashed_packet_queue) {
> +            avpriv_packet_list_free(&(mov->tracks[i].squashed_packet_queue),
> +                                    &(mov->tracks[i].squashed_packet_queue_end));
> +        }
>      }
>  
>      av_freep(&mov->tracks);
> @@ -6700,6 +6837,36 @@ static int mov_init(AVFormatContext *s)
>              }
>          } else if (st->codecpar->codec_type == AVMEDIA_TYPE_SUBTITLE) {
>              track->timescale = st->time_base.den;
> +
> +            if (track->par->codec_id == AV_CODEC_ID_TTML) {
> +                /* 14496-30 requires us to use a single sample per fragment
> +                   for TTML, for which we define a per-track flag.
> +
> +                   We set the flag in case we are receiving TTML paragraphs
> +                   from the input, in other words in case we are not doing
> +                   stream copy. */
> +                track->squash_fragment_samples_to_one =
> +                    ff_is_ttml_stream_paragraph_based(track->par);
> +
> +                if (mov->flags & FF_MOV_FLAG_FRAGMENT &&
> +                    track->squash_fragment_samples_to_one) {
> +                    av_log(s, AV_LOG_ERROR,
> +                           "Fragmentation is not currently supported for "
> +                           "TTML in MP4/ISMV (track synchronization between "
> +                           "subtitles and other media is not yet implemented)!\n");
> +                    return AVERROR_PATCHWELCOME;
> +                }
> +
> +                if (track->mode != MODE_ISM &&
> +                    track->par->codec_tag == MOV_ISMV_TTML_TAG &&
> +                    s->strict_std_compliance > FF_COMPLIANCE_UNOFFICIAL) {
> +                    av_log(s, AV_LOG_ERROR,
> +                           "ISMV style TTML support with the 'dfxp' tag in "
> +                           "non-ISMV formats is not officially supported. Add "
> +                           "'-strict unofficial' if you want to use it.\n");
> +                    return AVERROR_EXPERIMENTAL;
> +                }
> +            }
>          } else if (st->codecpar->codec_type == AVMEDIA_TYPE_DATA) {
>              track->timescale = st->time_base.den;
>          } else {
> @@ -7046,6 +7213,11 @@ static int mov_write_trailer(AVFormatContext *s)
>          }
>      }
>  
> +    // Check if we have any tracks that require squashing.
> +    // In that case, we'll have to write the packet here.
> +    if ((res = mov_write_squashed_packets(s)) < 0)
> +        return res;
> +
>      // If there were no chapters when the header was written, but there
>      // are chapters now, write them in the trailer.  This only works
>      // when we are not doing fragments.
> @@ -7190,6 +7362,8 @@ static const AVCodecTag codec_mp4_tags[] = {
>      { AV_CODEC_ID_MOV_TEXT,        MKTAG('t', 'x', '3', 'g') },
>      { AV_CODEC_ID_BIN_DATA,        MKTAG('g', 'p', 'm', 'd') },
>      { AV_CODEC_ID_MPEGH_3D_AUDIO,  MKTAG('m', 'h', 'm', '1') },
> +    { AV_CODEC_ID_TTML,            MOV_MP4_TTML_TAG          },
> +    { AV_CODEC_ID_TTML,            MOV_ISMV_TTML_TAG         },
>      { AV_CODEC_ID_NONE,               0 },
>  };
>  #if CONFIG_MP4_MUXER || CONFIG_PSP_MUXER
> @@ -7198,6 +7372,7 @@ static const AVCodecTag *const mp4_codec_tags_list[] = { codec_mp4_tags, NULL };
>  
>  static const AVCodecTag codec_ism_tags[] = {
>      { AV_CODEC_ID_WMAPRO      , MKTAG('w', 'm', 'a', ' ') },
> +    { AV_CODEC_ID_TTML        , MOV_ISMV_TTML_TAG         },
>      { AV_CODEC_ID_NONE        ,    0 },
>  };
>  
> diff --git a/libavformat/movenc.h b/libavformat/movenc.h
> index af1ea0bce6..95db1bf46d 100644
> --- a/libavformat/movenc.h
> +++ b/libavformat/movenc.h
> @@ -26,6 +26,7 @@
>  
>  #include "avformat.h"
>  #include "movenccenc.h"
> +#include "libavcodec/packet_internal.h"
>  
>  #define MOV_FRAG_INFO_ALLOC_INCREMENT 64
>  #define MOV_INDEX_CLUSTER_SIZE 1024
> @@ -164,6 +165,10 @@ typedef struct MOVTrack {
>      int pal_done;
>  
>      int is_unaligned_qt_rgb;
> +
> +    unsigned int squash_fragment_samples_to_one; //< flag to note formats where all samples for a fragment are to be squashed
> +
> +    PacketList *squashed_packet_queue, *squashed_packet_queue_end;
>  } MOVTrack;
>  
>  typedef enum {
> diff --git a/libavformat/movenc_ttml.c b/libavformat/movenc_ttml.c
> new file mode 100644
> index 0000000000..bf4a6fd89e
> --- /dev/null
> +++ b/libavformat/movenc_ttml.c
> @@ -0,0 +1,178 @@
> +/*
> + * MP4, ISMV Muxer TTML helpers
> + * Copyright (c) 2021 24i
> + *
> + * 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
> + */
> +
> +#include "avformat.h"
> +#include "avio_internal.h"
> +#include "isom.h"
> +#include "movenc.h"
> +#include "movenc_ttml.h"
> +#include "libavcodec/packet_internal.h"
> +
> +static const unsigned char empty_ttml_document[] =
> +    "<tt xml:lang=\"\" xmlns=\"http://www.w3.org/ns/ttml\" />";
> +
> +static int mov_init_ttml_writer(MOVTrack *track, AVFormatContext **out_ctx)
> +{
> +    AVStream *movenc_stream = track->st, *ttml_stream = NULL;
> +    AVFormatContext *ttml_ctx = NULL;
> +    int ret = AVERROR_BUG;
> +    if ((ret = avformat_alloc_output_context2(&ttml_ctx, NULL,
> +                                              "ttml", NULL)) < 0)
> +        return ret;
> +
> +    if ((ret = avio_open_dyn_buf(&ttml_ctx->pb)) < 0)
> +        goto fail;
> +
> +    if (!(ttml_stream = avformat_new_stream(ttml_ctx, NULL))) {
> +        ret = AVERROR(ENOMEM);
> +        goto fail;
> +    }
> +
> +    if ((ret = avcodec_parameters_copy(ttml_stream->codecpar,
> +                                       movenc_stream->codecpar)) < 0)
> +        goto fail;
> +
> +    ttml_stream->time_base = movenc_stream->time_base;
> +
> +    *out_ctx = ttml_ctx;
> +
> +    return 0;
> +
> +fail:
> +    ffio_free_dyn_buf(&ttml_ctx->pb);
> +    avformat_free_context(ttml_ctx);

If you used out_ctx directly (i.e. don't use ttml_ctx at all), you could
remove the cleanup code in
 this function and instead reuse the cleanup code in
 ff_mov_generate_squashed_ttml_packet().
 (But you will have to add a check for whether ttml_ctx exists in
ff_mov_generate_squashed_ttml_packet().)


> +
> +    return ret;
> +}
> +
> +static int mov_write_ttml_document_from_queue(AVFormatContext *s,
> +                                              AVFormatContext *ttml_ctx,
> +                                              MOVTrack *track,
> +                                              AVPacket *pkt,
> +                                              int64_t *out_start_ts,
> +                                              int64_t *out_duration)
> +{
> +    int ret = AVERROR_BUG;
> +    int64_t start_ts = track->start_dts == AV_NOPTS_VALUE ?
> +                       0 : (track->start_dts + track->track_duration);
> +    int64_t end_ts   = start_ts;
> +
> +    if ((ret = avformat_write_header(ttml_ctx, NULL)) < 0) {
> +        return ret;
> +    }
> +
> +    while (!avpriv_packet_list_get(&track->squashed_packet_queue,
> +                                   &track->squashed_packet_queue_end,
> +                                   pkt)) {
> +        end_ts = FFMAX(end_ts, pkt->pts + pkt->duration);
> +
> +        // in case of the 'dfxp' muxing mode, each written document is offset
> +        // to its containing sample's beginning.
> +        if (track->par->codec_tag == MOV_ISMV_TTML_TAG) {
> +            pkt->dts = pkt->pts = (pkt->pts - start_ts);
> +        }
> +
> +        pkt->stream_index = 0;
> +
> +        av_packet_rescale_ts(pkt, track->st->time_base,
> +                             ttml_ctx->streams[pkt->stream_index]->time_base);
> +
> +        if ((ret = av_write_frame(ttml_ctx, pkt)) < 0) {
> +            goto cleanup;
> +        }
> +
> +        av_packet_unref(pkt);
> +    }
> +
> +    if ((ret = av_write_trailer(ttml_ctx)) < 0)
> +        goto cleanup;
> +
> +    *out_start_ts = start_ts;
> +    *out_duration = end_ts - start_ts;
> +
> +    ret = 0;
> +
> +cleanup:
> +    return ret;
> +}
> +
> +int ff_mov_generate_squashed_ttml_packet(AVFormatContext *s,
> +                                         MOVTrack *track, AVPacket *pkt)
> +{
> +    AVFormatContext *ttml_ctx = NULL;
> +    // values for the generated AVPacket
> +    int64_t start_ts = 0;
> +    int64_t duration = 0;
> +
> +    int ret = AVERROR_BUG;
> +
> +    if ((ret = mov_init_ttml_writer(track, &ttml_ctx)) < 0) {
> +        av_log(s, AV_LOG_ERROR, "Failed to initialize the TTML writer: %s\n",
> +               av_err2str(ret));
> +        return ret;
> +    }
> +
> +    if (!track->squashed_packet_queue) {
> +        // empty queue, write minimal empty document with zero duration
> +        avio_write(ttml_ctx->pb, empty_ttml_document,
> +                   sizeof(empty_ttml_document) - 1);
> +        start_ts = 0;
> +        duration = 0;
> +        goto generate_packet;
> +    }
> +
> +    if ((ret = mov_write_ttml_document_from_queue(s, ttml_ctx, track, pkt,
> +                                                  &start_ts,
> +                                                  &duration)) < 0) {
> +        av_log(s, AV_LOG_ERROR,
> +               "Failed to generate a squashed TTML packet from the packet "
> +               "queue: %s\n",
> +               av_err2str(ret));
> +        goto cleanup;
> +    }
> +
> +generate_packet:
> +    {
> +        // Generate an AVPacket from the data written into the dynamic buffer.
> +        uint8_t *buf = NULL;
> +        int buf_len = avio_close_dyn_buf(ttml_ctx->pb, &buf);
> +        ttml_ctx->pb = NULL;
> +
> +        if ((ret = av_packet_from_data(pkt, buf, buf_len)) < 0) {
> +            av_log(s, AV_LOG_ERROR,
> +                   "Failed to create a TTML AVPacket from AVIO data: %s\n",
> +                   av_err2str(ret));
> +            av_freep(&buf);
> +            goto cleanup;
> +        }
> +
> +        pkt->pts = pkt->dts = start_ts;
> +        pkt->duration = duration;
> +        pkt->flags |= AV_PKT_FLAG_KEY;
> +    }
> +
> +    ret = 0;
> +
> +cleanup:
> +    ffio_free_dyn_buf(&ttml_ctx->pb);
> +    avformat_free_context(ttml_ctx);
> +    return ret;
> +}
> diff --git a/libavformat/movenc_ttml.h b/libavformat/movenc_ttml.h
> new file mode 100644
> index 0000000000..c71ecd0997
> --- /dev/null
> +++ b/libavformat/movenc_ttml.h
> @@ -0,0 +1,31 @@
> +/*
> + * MP4, ISMV Muxer TTML helpers
> + * Copyright (c) 2021 24i
> + *
> + * 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
> + */
> +
> +#ifndef AVFORMAT_MOVENC_TTML_H
> +#define AVFORMAT_MOVENC_TTML_H
> +
> +#include "avformat.h"
> +#include "movenc.h"
> +
> +int ff_mov_generate_squashed_ttml_packet(AVFormatContext *s,
> +                                         MOVTrack *track, AVPacket *pkt);
> +
> +#endif /* AVFORMAT_MOVENC_TTML_H */
> diff --git a/tests/fate/subtitles.mak b/tests/fate/subtitles.mak
> index ee65afe35b..880109f201 100644
> --- a/tests/fate/subtitles.mak
> +++ b/tests/fate/subtitles.mak
> @@ -109,6 +109,10 @@ fate-sub-dvb: CMD = framecrc -i $(TARGET_SAMPLES)/sub/dvbsubtest_filter.ts -map
>  FATE_SUBTITLES-$(call ALLYES, FILE_PROTOCOL PIPE_PROTOCOL SRT_DEMUXER SUBRIP_DECODER TTML_ENCODER TTML_MUXER) += fate-sub-ttmlenc
>  fate-sub-ttmlenc: CMD = fmtstdout ttml -i $(TARGET_SAMPLES)/sub/SubRip_capability_tester.srt
>  
> +FATE_SUBTITLES-$(call ALLYES, FILE_PROTOCOL SRT_DEMUXER MOV_DEMUXER SUBRIP_DECODER TTML_ENCODER TTML_MUXER MOV_MUXER) += fate-sub-ttml-mp4-stpp fate-sub-ttml-mp4-dfxp
> +fate-sub-ttml-mp4-stpp: CMD = transcode srt $(TARGET_SAMPLES)/sub/SubRip_capability_tester.srt mp4 "-map 0:s -c:s ttml -time_base:s 1:1000" "-map 0 -c copy" "" "-of json -show_entries packet:stream=index,codec_type,codec_tag_string,codec_tag,codec_name,time_base,start_time,duration_ts,duration,nb_frames,nb_read_packets:stream_tags"
> +fate-sub-ttml-mp4-dfxp: CMD = transcode srt $(TARGET_SAMPLES)/sub/SubRip_capability_tester.srt mp4 "-map 0:s -c:s ttml -time_base:s 1:1000 -tag:s dfxp -strict unofficial" "-map 0 -c copy" "" "-of json -show_entries packet:stream=index,codec_type,codec_tag_string,codec_tag,codec_name,time_base,start_time,duration_ts,duration,nb_frames,nb_read_packets:stream_tags"
> +
>  FATE_SUBTITLES-$(call ENCMUX, ASS, ASS) += $(FATE_SUBTITLES_ASS-yes)
>  FATE_SUBTITLES += $(FATE_SUBTITLES-yes)
>  
> diff --git a/tests/ref/fate/sub-ttml-mp4-dfxp b/tests/ref/fate/sub-ttml-mp4-dfxp
> new file mode 100644
> index 0000000000..0172e5b7e6
> --- /dev/null
> +++ b/tests/ref/fate/sub-ttml-mp4-dfxp
> @@ -0,0 +1,44 @@
> +2e7e01c821c111466e7a2844826b7f6d *tests/data/fate/sub-ttml-mp4-dfxp.mp4
> +8519 tests/data/fate/sub-ttml-mp4-dfxp.mp4
> +#tb 0: 1/1000
> +#media_type 0: data
> +#codec_id 0: none
> +0,          0,          0,    68500,     7866, 0x456c36b7
> +{
> +    "packets": [
> +        {
> +            "codec_type": "data",
> +            "stream_index": 0,
> +            "pts": 0,
> +            "pts_time": "0.000000",
> +            "dts": 0,
> +            "dts_time": "0.000000",
> +            "duration": 68500,
> +            "duration_time": "68.500000",
> +            "size": "7866",
> +            "pos": "44",
> +            "flags": "K_"
> +        }
> +    ],
> +    "programs": [
> +
> +    ],
> +    "streams": [
> +        {
> +            "index": 0,
> +            "codec_type": "data",
> +            "codec_tag_string": "dfxp",
> +            "codec_tag": "0x70786664",
> +            "time_base": "1/1000",
> +            "start_time": "0.000000",
> +            "duration_ts": 68500,
> +            "duration": "68.500000",
> +            "nb_frames": "1",
> +            "nb_read_packets": "1",
> +            "tags": {
> +                "language": "und",
> +                "handler_name": "SubtitleHandler"
> +            }
> +        }
> +    ]
> +}
> diff --git a/tests/ref/fate/sub-ttml-mp4-stpp b/tests/ref/fate/sub-ttml-mp4-stpp
> new file mode 100644
> index 0000000000..a5165b568d
> --- /dev/null
> +++ b/tests/ref/fate/sub-ttml-mp4-stpp
> @@ -0,0 +1,44 @@
> +cbd2c7ff864a663b0d893deac5a0caec *tests/data/fate/sub-ttml-mp4-stpp.mp4
> +8547 tests/data/fate/sub-ttml-mp4-stpp.mp4
> +#tb 0: 1/1000
> +#media_type 0: data
> +#codec_id 0: none
> +0,          0,          0,    68500,     7866, 0x456c36b7
> +{
> +    "packets": [
> +        {
> +            "codec_type": "data",
> +            "stream_index": 0,
> +            "pts": 0,
> +            "pts_time": "0.000000",
> +            "dts": 0,
> +            "dts_time": "0.000000",
> +            "duration": 68500,
> +            "duration_time": "68.500000",
> +            "size": "7866",
> +            "pos": "44",
> +            "flags": "K_"
> +        }
> +    ],
> +    "programs": [
> +
> +    ],
> +    "streams": [
> +        {
> +            "index": 0,
> +            "codec_type": "data",
> +            "codec_tag_string": "stpp",
> +            "codec_tag": "0x70707473",
> +            "time_base": "1/1000",
> +            "start_time": "0.000000",
> +            "duration_ts": 68500,
> +            "duration": "68.500000",
> +            "nb_frames": "1",
> +            "nb_read_packets": "1",
> +            "tags": {
> +                "language": "und",
> +                "handler_name": "SubtitleHandler"
> +            }
> +        }
> +    ]
> +}
> 



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