Describe the bug
When streaming video without audio to SRS via the RTMP protocol, the resulting HLS playback anomalously contains audio information, causing compatibility issues with some players. By adding the configuration 'hls_acodec an', the aforementioned anomaly can be resolved without affecting video streams that contain audio. Should we consider making 'hls_acodec an' the default value?

step1:
Using the RTMP protocol, push a video stream without audio to the SRS service.

step2:
While playing an HLS stream through VLC, it was discovered that the stream contains abnormal audio information.

step3:
Add the configuration: hls_acodec an.

step4:
Upon restreaming, it was observed that the abnormal audio information had disappeared.

step5:
Push a video stream with audio and test whether setting hls_acodec to 'an' will have an effect.

Version
Version number: SRS/5.0.x, 6.0.x, and so on.

TRANS_BY_GPT4