[FFmpeg-devel] [PATCH] avformat/hlsenc: Dont write stream info for agroup

[Dixit, Vishwanath]

On 1/18/18 2:39 PM, Brendan McGrath wrote:
> When using an 'agroup' within var_stream_map - the audio stream is
> being added to the master playlist file as both an audio rendition
> and an individual stream (with an AUDIO reference back to itself).
>
> This patch ensures an audio rendition does not also appear within
> the stream info list.
>
> What follows is an example of the command to create this issue and
> the contents of the master playlist before and after this patch is
> applied:
>
> ffmpeg -i in.ts -b:a:0 128k -b:v:0 1800k -b:v:1 1024k -map 0:a \
> -map 0:v -map 0:v -f hls -var_stream_map "a:0,agroup:audio_0 "\
> "v:0,agroup:audio_0 v:1,agroup:audio_0" -master_pl_name \
> tv_hls.m3u8 tv_hls_%v.m3u8
>
> Before:
>  #EXTM3U
>  #EXT-X-VERSION:3
>  #EXT-X-MEDIA:TYPE=AUDIO,GROUP-ID="group_audio_0",NAME="audio_0",DEFAULT=YES,URI="tv_hls_0.m3u8"
>  #EXT-X-STREAM-INF:BANDWIDTH=140800,AUDIO="group_audio_0"
>  tv_hls_0.m3u8
>
>  #EXT-X-STREAM-INF:BANDWIDTH=2120800,RESOLUTION=1920x1080,AUDIO="group_audio_0"
>  tv_hls_1.m3u8
>
>  #EXT-X-STREAM-INF:BANDWIDTH=1267200,RESOLUTION=1920x1080,AUDIO="group_audio_0"
>  tv_hls_2.m3u8
>
> After:
>  #EXTM3U
>  #EXT-X-VERSION:3
>  #EXT-X-MEDIA:TYPE=AUDIO,GROUP-ID="group_audio_0",NAME="audio_0",DEFAULT=YES,URI="tv_hls_0.m3u8"
>  #EXT-X-STREAM-INF:BANDWIDTH=2120800,RESOLUTION=1920x1080,AUDIO="group_audio_0"
>  tv_hls_1.m3u8
>
>  #EXT-X-STREAM-INF:BANDWIDTH=1267200,RESOLUTION=1920x1080,AUDIO="group_audio_0"
>  tv_hls_2.m3u8
>
> Signed-off-by: Brendan McGrath <redmcg at redmandi.dyndns.org>
> ---
>
Some use cases may need audio only variant streams. Ex: when bandwidth is too low. Also, I think the playback issue you are seeing, is because of AUDIO referencing back to itself, but, not because of audio only variant stream. So, instead of completely removing the audio only variant streams, you can just remove the self-referencing attribute (AUDIO=) from the #EXT-X-STREAM-INF tag’s attribute list, for the audio only variant streams.
#EXTM3U
#EXT-X-VERSION:3
#EXT-X-MEDIA:TYPE=AUDIO,GROUP-ID="group_audio_0",NAME="audio_0",DEFAULT=YES,URI="tv_hls_0.m3u8"
#EXT-X-STREAM-INF:BANDWIDTH=140800
tv_hls_0.m3u8

#EXT-X-STREAM-INF:BANDWIDTH=2120800,RESOLUTION=1920x1080,AUDIO="group_audio_0"
tv_hls_1.m3u8

#EXT-X-STREAM-INF:BANDWIDTH=1267200,RESOLUTION=1920x1080,AUDIO="group_audio_0"
tv_hls_2.m3u8


> Pre-patch - the hls stream I was testing would not play on the iOS devices I was testing with.
>
> With the patch applied - they now play the stream
>
>  libavformat/hlsenc.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/libavformat/hlsenc.c b/libavformat/hlsenc.c
> index e36120c..a75853b 100644
> --- a/libavformat/hlsenc.c
> +++ b/libavformat/hlsenc.c
> @@ -1172,6 +1172,9 @@ static int create_master_playlist(AVFormatContext *s,
>      for (i = 0; i < hls->nb_varstreams; i++) {
>          vs = &(hls->var_streams[i]);
>  
> +        if (!vs->has_video && !vs->has_subtitle && vs->agroup)
> +            continue;
> +
>          m3u8_name_size = strlen(vs->m3u8_name) + 1;
>          m3u8_rel_name = av_malloc(m3u8_name_size);
>          if (!m3u8_rel_name) {