Questions about downlaoding LIVE HLS streams and problems

Question

First, I wanna admit that I am not a programmer. I am only end user. Since I can't find answers I found Stackoverflow where I see many experts who can answer me. So here I go.

I am trying to download HLS LIVE streams(not pre-recorded videos like youtube, but LIVE like sports game broadcasts over tv channels). I am using downloader programs that downloads pre-recored videos but problem with LIVE streams.

I understand PART files are downloaded and in the end PART is appended/aggregated/converted(?) as final MP4 file.

Here's the problem.
Sometimes I get MP4 files that looks good, I see in file properties, file size, details, etc.. I am using VLC, Movies&tv, MPC-HC, MPV, Potplayer, windows media player, etc..

Problem #1: Some don;t have either video or audio, plays only one, video or audio. why?

Problem #2: Some MP4 don't play at all, corrupted file? File properties details show no video or audio details. VLC says cannot find, Movies&tv error code, MPV don;t even open, etc.. Interesting. when i use MPV player to play MP4 file, i can see skipping cus time jumps (ex: 10:12 to 10:23) but keeps playing(this is why MPV is the beat player). So there was some sort of buffer, error with PART file?

Problem #3: MP4 plays but skips, freezes during play. Why?

I am thinking internet speed and quality might have something to do with these problems but I don;t know. My bandwidth meter shows around 1mbps during download, I have 8mbps service.

Or this there problem with PART files and trouble during append/aggregate/convert process to final MP4 file?

what exactly is happens during append/aggregate/convert process?

Also Downloader gives me several options (variants?? usually two options) so I tried to down both streams. Few times entire 100% of MP4 plays perfectly. But often problems. Sometimes each final MP4 files plays differently. If skipping then each file skips at different places. I downloaded at same time. Then one option stops, no MP4 file, but other options downloads till end I get MP4.

Just to repeat(cus people seem to be confused). I am asking about LIVE stream(endless broadcast streams), not pre-taped videos like youtube or movie/tv show download sites. Also think of tv channel broadcasting LIVE sports game and later re-broadcast same game pre-taped but still broadcasting in tv channels. It' HLS stream.

Sorry for long post but I wanna give helpers all possible information to help me. Thanks in advance

Answer 1

I understand PART files are downloaded and in the end PART is appended/aggregated/converted(?) as final MP4 file.

HLS has two main parts. The playlist (usually named with .m3u8), and the segments (usually .mp4, .m4v, .m4a).

The playlist tells the client where the segments are, and the segments are essentially concatenated together to form the final stream.

Problem #1: Some don;t have either video or audio, plays only one, video or audio. why?

It's typical in HLS to split the audio and video segments in separate files. For example, you might have a 128 kbps audio stream for all variations, but 3 Mbps, 5 Mbps, and 10 Mbps video streams. Rather than uploading a copy of the audio for each variation, one can be uploaded and used for all.

Problem #2: Some MP4 don't play at all, corrupted file?

You're probably missing some initialization data found in another segment.

Problem #3: MP4 plays but skips, freezes during play. Why?

No different than Problem #2.

Or this there problem with PART files and trouble during append/aggregate/convert process to final MP4 file?

Yes.

Also Downloader gives me several options (variants?? usually two options) so I tried to down both streams. Few times entire 100% of MP4 plays perfectly. But often problems. Sometimes each final MP4 files plays differently.

This will generally be different bitrates of the same stream. It's common with HLS and DASH to upload multiple bitrates so the client can switch up/down to various qualities as it has bandwidth available.

Also note that you might be running into DRM, non-standard HLS, broken encoders, a broken downloader, data running at an unexpected rate, etc. etc.