[FFmpeg-trac] #7403(avformat:reopened): HLS Master Playlist fails being generated correctly

[FFmpeg]

#7403: HLS Master Playlist fails being generated correctly
------------------------------------+------------------------------------
             Reporter:  barhom      |                    Owner:  (none)
                 Type:  defect      |                   Status:  reopened
             Priority:  minor       |                Component:  avformat
              Version:  git-master  |               Resolution:
             Keywords:  hls         |               Blocked By:
             Blocking:              |  Reproduced by developer:  1
Analyzed by developer:  0           |
------------------------------------+------------------------------------
Comment (by alexey.rodionov):

 It's definitely a bug. And here's why:

 I'm working on a service that takes a video file as input and generates
 HLS streams in various resolutions as output (like YouTube does).

 If the input file has no audio, running the following command:

 {{{
 ffmpeg -i input.mp4 -map 0:v:0 -map 0:v:0 -map 0:v:0 -map 0:v:0
 -filter:v:0 scale=-2:360 -filter:v:1 scale=-2:480 -filter:v:2 scale=-2:720
 -filter:v:3 scale=-2:1080 -f hls -hls_playlist_type vod -hls_flags
 independent_segments -master_pl_name master.m3u8 -hls_segment_filename
 stream_%v/chunk_%08d.ts -strftime_mkdir 1 -var_stream_map "v:0,name:360p
 v:1,name:480p v:2,name:720p v:3,name:1080p" stream_%v.m3u8
 }}}

 causes the following warning(s):

 {{{
 Bandwidth info not available, set audio and video bitrates
     Last message repeated 3 times
 }}}

 and produce the following broken HLS master playlist:

 {{{
 #EXTM3U
 #EXT-X-VERSION:6
 }}}

 This can be fixed by specifying the bitrate explicitly, e.g. `-b:v:0 1000k
 -b:v:1 2000k -b:v:2 4000k -b:v:3 6000k`.

 But I don't want to explicitly specify the video bitrate for each stream.
 I want to use ffmpeg's default values. By the way, I don't know the
 ffmpeg's default values for various resolutions. Moreover, to get a high-
 quality output video, I need to consider not only the resolution, but also
 the frame rate. E.g., a video with 60 fps needs a higher bitrate than a
 video with the same resolution but 30 fps. And the problem is that I don't
 know the frame rate of the input video that the user can upload.

 The interesting thing is that there is another way to create an HLS
 streams using `dash` muxer with `-hls_playlist true` option:

 {{{
 ffmpeg -i input.mp4 -map 0:v:0 -map 0:v:0 -map 0:v:0 -map 0:v:0
 -filter:v:0 scale=-2:360 -filter:v:1 scale=-2:480 -filter:v:2 scale=-2:720
 -filter:v:3 scale=-2:1080 -use_template 1 -use_timeline 1 -adaptation_sets
 "id=0,streams=v" -f dash -hls_playlist true manifest.mpd
 }}}

 This also causes the following warning(s):

 {{{
 [dash @ 000001fe89d20cc0] No bit rate set for stream 0
 [dash @ 000001fe89d20cc0] No bit rate set for stream 1
 [dash @ 000001fe89d20cc0] No bit rate set for stream 2
 [dash @ 000001fe89d20cc0] No bit rate set for stream 3
 }}}

 but produce the following correct `master.m3u8` HLS master playlist
 (alongside `manifest.mpd` DASH master playlist):

 {{{
 #EXTM3U
 #EXT-X-VERSION:7
 #EXT-X-STREAM-INF:BANDWIDTH=987359,RESOLUTION=640x360,CODECS="avc1.64001f"
 media_0.m3u8

 #EXT-X-STREAM-
 INF:BANDWIDTH=1504372,RESOLUTION=854x480,CODECS="avc1.64001f"
 media_1.m3u8

 #EXT-X-STREAM-
 INF:BANDWIDTH=2787800,RESOLUTION=1280x720,CODECS="avc1.640020"
 media_2.m3u8

 #EXT-X-STREAM-
 INF:BANDWIDTH=5181173,RESOLUTION=1920x1080,CODECS="avc1.64002a"
 media_3.m3u8
 }}}

 This means that ffmpeg actually has all the info about video bitrate it
 needs and that this is definitely a bug in `hls` muxer that expects the
 user to specify the bitrate explicitly.

 Moreover, if the `hls` muxer is used, but the input video file has audio,
 running the following command:

 {{{
 ffmpeg -i input.mp4 -map 0:v:0 -map 0:v:0 -map 0:v:0 -map 0:v:0 -map 0:a:0
 -filter:v:0 scale=-2:360 -filter:v:1 scale=-2:480 -filter:v:2 scale=-2:720
 -filter:v:3 scale=-2:1080 -f hls -hls_playlist_type vod -hls_flags
 independent_segments -master_pl_name master.m3u8 -hls_segment_filename
 stream_%v/chunk_%08d.ts -strftime_mkdir 1 -var_stream_map
 "v:0,name:360p,agroup:audio v:1,name:480p,agroup:audio
 v:2,name:720p,agroup:audio v:3,name:1080p,agroup:audio
 a:0,name:audio,agroup:audio" stream_%v.m3u8
 }}}

 doesn't cause any warnings and produce the following master playlist:

 {{{
 #EXTM3U
 #EXT-X-VERSION:6
 #EXT-X-MEDIA:TYPE=AUDIO,GROUP-
 ID="group_audio",NAME="audio_4",DEFAULT=YES,URI="stream_audio.m3u8"
 #EXT-X-STREAM-
 INF:BANDWIDTH=140800,RESOLUTION=640x360,CODECS="avc1.64001f,mp4a.40.2",AUDIO="group_audio"
 stream_360p.m3u8

 #EXT-X-STREAM-
 INF:BANDWIDTH=140800,RESOLUTION=854x480,CODECS="avc1.64001f,mp4a.40.2",AUDIO="group_audio"
 stream_480p.m3u8

 #EXT-X-STREAM-
 INF:BANDWIDTH=140800,RESOLUTION=1280x720,CODECS="avc1.640020,mp4a.40.2",AUDIO="group_audio"
 stream_720p.m3u8

 #EXT-X-STREAM-
 INF:BANDWIDTH=140800,RESOLUTION=1920x1080,CODECS="avc1.64002a,mp4a.40.2",AUDIO="group_audio"
 stream_1080p.m3u8

 #EXT-X-STREAM-INF:BANDWIDTH=140800,CODECS="mp4a.40.2",AUDIO="group_audio"
 stream_audio.m3u8
 }}}

 But all video streams have the same bandwidth as the audio stream that is
 obviously incorrect.
-- 
Ticket URL: <https://trac.ffmpeg.org/ticket/7403#comment:13>
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