Parsing HLS m3u8 file using regular expressions

Question

I want to parse HLS master m3u8 file and get the bandwidth, resolution and file name from it. Currently i am using String parsing to search string for some patterns and do the sub string to get value.

Example File:

#EXTM3U
#EXT-X-STREAM-INF:PROGRAM-ID=1,BANDWIDTH=476416,RESOLUTION=416x234
Stream1/index.m3u8
#EXT-X-STREAM-INF:PROGRAM-ID=1,BANDWIDTH=763319,RESOLUTION=480x270
Stream2/index.m3u8
#EXT-X-STREAM-INF:PROGRAM-ID=1,BANDWIDTH=1050224,RESOLUTION=640x360
Stream3/index.m3u8
#EXT-X-STREAM-INF:PROGRAM-ID=1,BANDWIDTH=1910937,RESOLUTION=640x360
Stream4/index.m3u8
#EXT-X-STREAM-INF:PROGRAM-ID=1,BANDWIDTH=3775816,RESOLUTION=1280x720
Stream5/index.m3u8

But i found that we can parse it using regular expressions like mentioned in this question: Problem matching regex pattern in Android

I don't have any Idea of regular expression so can some one please guide me to parse this using regular expression.

Or can someone help me in writing regexp for parsing out BANDWIDTH and RESOLUTION values from below string

#EXT-X-STREAM-INF:PROGRAM-ID=1,BANDWIDTH=476416,RESOLUTION=416x234

Answer 1

You could try something like this:

    final Pattern pattern = Pattern.compile("^#EXT-X-STREAM-INF:.*BANDWIDTH=(\\d+).*RESOLUTION=([\\dx]+).*");

    Matcher matcher = pattern.matcher("#EXT-X-STREAM-INF:PROGRAM-ID=1,BANDWIDTH=476416,RESOLUTION=416x234");
    String bandwidth = "";
    String resolution = "";

    if (matcher.find()) {
        bandwidth = matcher.group(1);
        resolution = matcher.group(2);
    }

Would set bandwidth and resolution to the correct (String) values.

I haven't tried this on an android device or emulator, but judging from the link you sent and the android API it should work the same as the above plain old java.

The regex matches strings starting with #EXT-X-STREAM-INF: and contains BANDWIDTH and RESOLUTION followed by the correct value formats. These are then back-referenced in back-reference group 1 and 2 so we can extract them.

Edit:

If RESOLUTION isn't always present then you can make that portion optional as such:

"^#EXT-X-STREAM-INF:.*BANDWIDTH=(\\d+).*(?:RESOLUTION=([\\dx]+))?.*"

The resolution string would be null in cases where only BANDWIDTH is present.

Edit2:

? makes things optional, and (?:___) means a passive group (as opposed to a back-reference group (___). So it's basically a optional passive group. So yes, anything inside it will be optional.

A . matches a single character, and a * makes means it will be repeated zero or more times. So .* will match zero or more characters. The reason we need this is to consume anything between what we are matching, e.g. anything between #EXT-X-STREAM-INF: and BANDWIDTH. There are many ways of doing this but .* is the most generic/broad one.

\d is basically a set of characters that represent numbers (0-9), but since we define the string as a Java string, we need the double \\, otherwise the Java compiler will fail because it does not recognize the escaped character \d (in Java). Instead it will parse \\ into \ so that we get \d in the final string passed to the Pattern constructor.

[\dx]+ means one or more characters (+) out of the characters 0-9 and x. [\dx\d] would be a single character (no +) out of the same set of characters.

If you are interested in regex you could check out regular-expressions.info or/and regexone.com, there you will find much more in depth answers to all your questions.