HLS output master playlist emits BANDWIDTH=0 and plain opus CODECS #407

Summary

HlsOutputFormat can generate a master playlist with BANDWIDTH=0 and a plain opus codec string in CODECS.

This appears to cause Safari/iOS to reject the master playlist before requesting the child media playlist.

Example output

Generated master.m3u8:

#EXTM3U

#EXT-X-STREAM-INF:BANDWIDTH=0,CODECS="avc1.640015,opus",RESOLUTION=480x270
playlist-1.m3u8

Problems

There seem to be two compatibility issues here:

1. BANDWIDTH=0

   HLS clients expect BANDWIDTH to be a positive integer. Safari/iOS appears to reject this master playlist and does not proceed to request playlist-1.m3u8.

2. CODECS="...,opus"

   For Opus in MP4/CMAF/fMP4 HLS, the codec string should be RFC 6381-compatible. I believe plain opus is not accepted by Safari's HLS parser here, and the expected string is likely mp4a.ad.

Expected behavior

The generated master playlist should use Safari/iOS-compatible attributes, for example:

#EXT-X-STREAM-INF:BANDWIDTH=396000,CODECS="avc1.640015,mp4a.ad",RESOLUTION=480x270
playlist-1.m3u8

More generally:

• BANDWIDTH should never be 0; it should be a positive estimated peak bitrate.
• CODECS should contain RFC 6381-compatible codec strings.
• AVC should remain in full form, such as avc1.640015.
• Opus in MP4/CMAF HLS should not be emitted as plain opus; it should likely be mp4a.ad.

Environment

• Mediabunny version: 1.46.0
• Output format: HlsOutputFormat
• Segment format: CMAF/fMP4
• Playback issue observed in Safari/iOS native HLS playback

Additional context

In the consuming app, macOS Safari can play some outputs, but iPhone Safari reports native media failure:

MediaError code 4 / MEDIA_ERR_SRC_NOT_SUPPORTED

The iPhone/Safari player does not appear to request the child media playlist, which suggests the master playlist itself is being rejected.

I worked around this downstream by patching the generated master playlist to:

• replace BANDWIDTH=0 with a positive estimated aggregate bitrate
• replace plain opus in CODECS with mp4a.ad

After that patch, the generated master playlist looks like:

#EXT-X-STREAM-INF:BANDWIDTH=473600,CODECS="avc1.64000c,mp4a.ad",RESOLUTION=320x180,AUDIO="audio-3"
playlist-2.m3u8

Possible source locations

From the distributed package, the master playlist writer appears to generate these values around:

• dist/modules/src/hls/hls-muxer.js
  • writes BANDWIDTH=${Math.ceil(totalPeakBitrate)}
  • writes CODECS="${codecs.join(',')}"

Also, buildAudioCodecString appears to return plain "opus" for Opus, which may be correct in some contexts but seems incompatible with HLS master playlist CODECS for fMP4/CMAF playback in Safari.