[FFmpeg-devel] [PATCH v2 2/2] avformat/dashenc: Added support for Low-latency HLS(Experimental)

[Jeyapal, Karthick]

On 12/12/18 9:50 PM, Karthick J wrote:
> Apple doesn't have an official spec for LHLS. Meanwhile hls.js player folks are
> trying to standardize a open LHLS spec. The draft spec is available in https://github.com/video-dev/hlsjs-rfcs/blob/lhls-spec/proposals/0001-lhls.md
> This option will also try to comply with the above open spec, till Apple's spec officially supports it.
> Applicable only when @var{streaming} and @var{hls_playlist} options are enabled.
> ---
>  doc/muxers.texi       |  8 ++++++++
>  libavformat/dashenc.c | 37 +++++++++++++++++++++++++++++++++----
>  2 files changed, 41 insertions(+), 4 deletions(-)
>
> diff --git a/doc/muxers.texi b/doc/muxers.texi
> index 809f88662e..4ed46a2220 100644
> --- a/doc/muxers.texi
> +++ b/doc/muxers.texi
> @@ -305,6 +305,14 @@ If this flag is set, the dash segment files will be in in WebM format.
>  @item -ignore_io_errors @var{ignore_io_errors}
>  Ignore IO errors during open and write. Useful for long-duration runs with network output.
>  
> + at item -lhls @var{lhls}
> +Enable Low-latency HLS(LHLS). Adds #EXT-X-PREFETCH tag with current segment's URI.
> +Apple doesn't have an official spec for LHLS. Meanwhile hls.js player folks are
> +trying to standardize a open LHLS spec. The draft spec is available in https://github.com/video-dev/hlsjs-rfcs/blob/lhls-spec/proposals/0001-lhls.md
> +This option will also try to comply with the above open spec, till Apple's spec officially supports it.
> +Applicable only when @var{streaming} and @var{hls_playlist} options are enabled.
> +This is an experimental feature.
> +
>  @end table
>  
>  @anchor{framecrc}
> diff --git a/libavformat/dashenc.c b/libavformat/dashenc.c
> index f797b7bd1c..cfd0f601d4 100644
> --- a/libavformat/dashenc.c
> +++ b/libavformat/dashenc.c
> @@ -139,6 +139,7 @@ typedef struct DASHContext {
>      char *format_options_str;
>      SegmentType segment_type_option;  /* segment type as specified in options */
>      int ignore_io_errors;
> +    int lhls;
>  } DASHContext;
>  
>  static struct codec_string {
> @@ -418,7 +419,8 @@ static void get_start_index_number(OutputStream *os, DASHContext *c,
>  }
>  
>  static void write_hls_media_playlist(OutputStream *os, AVFormatContext *s,
> -                                     int representation_id, int final) {
> +                                     int representation_id, int final,
> +                                     char *prefetch_url) {
>      DASHContext *c = s->priv_data;
>      int timescale = os->ctx->streams[0]->time_base.den;
>      char temp_filename_hls[1024];
> @@ -431,6 +433,11 @@ static void write_hls_media_playlist(OutputStream *os, AVFormatContext *s,
>      int i, start_index, start_number;
>  
>      get_start_index_number(os, c, &start_index, &start_number);
> +
> +    if (!c->hls_playlist || start_index >= os->nb_segments ||
> +        os->segment_type != SEGMENT_TYPE_MP4)
> +        return;
> +
>      get_hls_playlist_name(filename_hls, sizeof(filename_hls),
>                            c->dirname, representation_id);
>  
> @@ -468,6 +475,9 @@ static void write_hls_media_playlist(OutputStream *os, AVFormatContext *s,
>          }
>      }
>  
> +    if (prefetch_url)
> +        avio_printf(c->m3u8_out, "#EXT-X-PREFETCH:%s\n", prefetch_url);
> +
>      if (final)
>          ff_hls_write_end_list(c->m3u8_out);
>  
> @@ -594,9 +604,8 @@ static void output_segment_list(OutputStream *os, AVIOContext *out, AVFormatCont
>          }
>          avio_printf(out, "\t\t\t\t</SegmentList>\n");
>      }
> -    if (c->hls_playlist && start_index < os->nb_segments && os->segment_type == SEGMENT_TYPE_MP4)
> -    {
> -        write_hls_media_playlist(os, s, representation_id, final);
> +    if (!c->lhls || final) {
> +        write_hls_media_playlist(os, s, representation_id, final, NULL);
>      }
>  
>  }
> @@ -1054,6 +1063,21 @@ static int dash_init(AVFormatContext *s)
>          c->seg_duration = c->min_seg_duration;
>      }
>  #endif
> +    if (c->lhls && s->strict_std_compliance > FF_COMPLIANCE_EXPERIMENTAL) {
> +        av_log(s, AV_LOG_ERROR,
> +               "LHLS is experimental, Please set -strict experimental in order to enable it.\n");
> +        return AVERROR_EXPERIMENTAL;
> +    }
> +
> +    if (c->lhls && !c->streaming) {
> +        av_log(s, AV_LOG_WARNING, "LHLS option will be ignored as streaming is not enabled\n");
> +        c->lhls = 0;
> +    }
> +
> +    if (c->lhls && !c->hls_playlist) {
> +        av_log(s, AV_LOG_WARNING, "LHLS option will be ignored as hls_playlist is not enabled\n");
> +        c->lhls = 0;
> +    }
>  
>      av_strlcpy(c->dirname, s->url, sizeof(c->dirname));
>      ptr = strrchr(c->dirname, '/');
> @@ -1635,6 +1659,10 @@ static int dash_write_packet(AVFormatContext *s, AVPacket *pkt)
>          if (ret < 0) {
>              return handle_io_open_error(s, ret, os->temp_path);
>          }
> +        if (c->lhls) {
> +            char *prefetch_url = use_rename ? NULL : os->filename;
> +            write_hls_media_playlist(os, s, pkt->stream_index, 0, prefetch_url);
> +        }
>      }
>  
>      //write out the data immediately in streaming mode
> @@ -1760,6 +1788,7 @@ static const AVOption options[] = {
>      { "mp4", "make segment file in ISOBMFF format", 0, AV_OPT_TYPE_CONST, {.i64 = SEGMENT_TYPE_MP4 }, 0, UINT_MAX,   E, "segment_type"},
>      { "webm", "make segment file in WebM format", 0, AV_OPT_TYPE_CONST, {.i64 = SEGMENT_TYPE_WEBM }, 0, UINT_MAX,   E, "segment_type"},
>      { "ignore_io_errors", "Ignore IO errors during open and write. Useful for long-duration runs with network output", OFFSET(ignore_io_errors), AV_OPT_TYPE_BOOL, { .i64 = 0 }, 0, 1, E },
> +    { "lhls", "Enable Low-latency HLS(Experimental). Adds #EXT-X-PREFETCH tag with current segment's URI", OFFSET(lhls), AV_OPT_TYPE_BOOL, { .i64 = 0 }, 0, 1, E },
>      { NULL },
>  };
>  

Pushed Patchset.

Regards,
Karthick