ABR behavior with mixed Codec (HEVC / AVC) HLS Livestreams

[reformhaus]

We are testing mixed codec livestreams (AVC / HEVC) in conjunction with Exoplayer. In this case, we currently only offer HEVC renditions in higher bandwidths. Sample Manifest:

#EXTM3U
#EXT-X-VERSION:4
#EXT-X-INDEPENDENT-SEGMENTS
#EXT-X-STREAM-INF:BANDWIDTH=2182400,AVERAGE-BANDWIDTH=1900800,CODECS="avc1.4d401f,mp4a.40.2",RESOLUTION=960x540,FRAME-RATE=50.000,AUDIO="aaclc",SUBTITLES="subs"
master-540p-1600-avc.m3u8
#EXT-X-I-FRAME-STREAM-INF:BANDWIDTH=1020800,AVERAGE-BANDWIDTH=880000,CODECS="avc1.4d401f",RESOLUTION=960x540,FRAME-RATE=50.000,URI="master-540p-1600-avc_I-Frame.m3u8"
#EXT-X-STREAM-INF:BANDWIDTH=2692800,AVERAGE-BANDWIDTH=2340800,CODECS="hvc1.1.6.L93.B0,mp4a.40.2",RESOLUTION=960x540,FRAME-RATE=50.000,AUDIO="aaclc",SUBTITLES="subs"
master-540p-2000-hevc.m3u8
#EXT-X-I-FRAME-STREAM-INF:BANDWIDTH=1276000,AVERAGE-BANDWIDTH=1100000,CODECS="hvc1.1.6.L93.B0",RESOLUTION=960x540,FRAME-RATE=50.000,URI="master-540p-2000-hevc_I-Frame.m3u8"
#EXT-X-STREAM-INF:BANDWIDTH=4606800,AVERAGE-BANDWIDTH=3990800,CODECS="hvc1.1.6.L123.B0,mp4a.40.2",RESOLUTION=1920x1080,FRAME-RATE=50.000,AUDIO="aaclc",SUBTITLES="subs"
master-1080p-3500-hevc.m3u8
#EXT-X-I-FRAME-STREAM-INF:BANDWIDTH=2233000,AVERAGE-BANDWIDTH=1925000,CODECS="hvc1.1.6.L123.B0",RESOLUTION=1920x1080,FRAME-RATE=50.000,URI="master-1080p-3500-hevc_I-Frame.m3u8"
#EXT-X-STREAM-INF:BANDWIDTH=6520800,AVERAGE-BANDWIDTH=5640800,CODECS="avc1.64002a,mp4a.40.2",RESOLUTION=1920x1080,FRAME-RATE=50.000,AUDIO="aaclc",SUBTITLES="subs"
master-1080p-5000-avc.m3u8
#EXT-X-I-FRAME-STREAM-INF:BANDWIDTH=3190000,AVERAGE-BANDWIDTH=2750000,CODECS="avc1.64002a",RESOLUTION=1920x1080,FRAME-RATE=50.000,URI="master-1080p-5000-avc_I-Frame.m3u8"
#EXT-X-STREAM-INF:BANDWIDTH=3330800,AVERAGE-BANDWIDTH=2890800,CODECS="hvc1.1.6.L120.B0,mp4a.40.2",RESOLUTION=1280x720,FRAME-RATE=50.000,AUDIO="aaclc",SUBTITLES="subs"
master-720p-2500-hevc.m3u8
#EXT-X-I-FRAME-STREAM-INF:BANDWIDTH=1595000,AVERAGE-BANDWIDTH=1375000,CODECS="hvc1.1.6.L120.B0",RESOLUTION=1280x720,FRAME-RATE=50.000,URI="master-720p-2500-hevc_I-Frame.m3u8"
#EXT-X-STREAM-INF:BANDWIDTH=4224000,AVERAGE-BANDWIDTH=3660800,CODECS="avc1.640020,mp4a.40.2",RESOLUTION=1280x720,FRAME-RATE=50.000,AUDIO="aaclc",SUBTITLES="subs"
master-720p-3200-avc.m3u8
#EXT-X-I-FRAME-STREAM-INF:BANDWIDTH=2041600,AVERAGE-BANDWIDTH=1760000,CODECS="avc1.640020",RESOLUTION=1280x720,FRAME-RATE=50.000,URI="master-720p-3200-avc_I-Frame.m3u8"
#EXT-X-STREAM-INF:BANDWIDTH=1672000,AVERAGE-BANDWIDTH=1460800,CODECS="avc1.4d401f,mp4a.40.2",RESOLUTION=640x360,FRAME-RATE=50.000,AUDIO="aaclc",SUBTITLES="subs"
master-360p-1200-avc.m3u8
#EXT-X-I-FRAME-STREAM-INF:BANDWIDTH=765600,AVERAGE-BANDWIDTH=660000,CODECS="avc1.4d401f",RESOLUTION=640x360,FRAME-RATE=50.000,URI="master-360p-1200-avc_I-Frame.m3u8"
#EXT-X-STREAM-INF:BANDWIDTH=1034000,AVERAGE-BANDWIDTH=910800,CODECS="avc1.4d401e,mp4a.40.2",RESOLUTION=480x270,FRAME-RATE=50.000,AUDIO="aaclc",SUBTITLES="subs"
master-270p-700-avc.m3u8
#EXT-X-I-FRAME-STREAM-INF:BANDWIDTH=446600,AVERAGE-BANDWIDTH=385000,CODECS="avc1.4d401e",RESOLUTION=480x270,FRAME-RATE=50.000,URI="master-270p-700-avc_I-Frame.m3u8"

#EXT-X-MEDIA:TYPE=AUDIO,LANGUAGE="de",NAME="Deutsch",AUTOSELECT=YES,DEFAULT=YES,CHANNELS="2",GROUP-ID="aaclc",URI="master-audio1-128-aaclc.m3u8"
#EXT-X-MEDIA:TYPE=AUDIO,LANGUAGE="de",NAME="Audiodeskription",AUTOSELECT=YES,DEFAULT=NO,CHARACTERISTICS="public.accessibility.describes-video",CHANNELS="2",GROUP-ID="aaclc",URI="master-audio2-128-aaclc.m3u8"


#EXT-X-MEDIA:TYPE=SUBTITLES,NAME="Deutsch",DEFAULT=YES,AUTOSELECT=YES,FORCED=NO,LANGUAGE="de",GROUP-ID="subs",URI="master-sub1.m3u8"

In our tests on HEVC-enabled devices with limited download bandwidth (1.6 Mbps), we found that Exoplayer continues to attempt to play the lowest HEVC renditions (960x540p50). As the download bandwidth is not sufficient, buffering events occur.

Our question: Is it intended that Exoplayer remains in the HEVC codec in its ABR behavior with the given HLS rendition set and does not automatically use a low AVC bandwidth, which would allow smooth playback with limited bandwidth?

Thanks in advance for any information.

Julian