/// <summary>
/// Downloads video's embed page and extracts useful data.
/// </summary>
protected virtual async Task <YouTubeEmbedPageData> DownloadEmbedPage(string id)
{
var result = new YouTubeEmbedPageData();
// get embed uri
var embedUri = GetYouTubeEmbedUri(id);
// download embed page
var client = HttpHelper.CreateClient();
var embedPageContent = await client.GetStringAsync(embedUri);
// find base.js
var match = BaseJsLocatorRegex.Match(embedPageContent);
if (!match.Success)
{
throw new GrabParseException("Failed to find base.js script reference.");
}
result.BaseJsUri = new Uri(embedUri, match.Groups[1].Value);
return(result);
}
/// <summary>
/// Invoked by <see cref="GrabAsync"/> method when the target video has a signature.
/// This method downloads the necessary script (base.js) and decipher all grabbed links.
/// </summary>
protected virtual async Task Decipher(YouTubeEmbedPageData embedPageData, YouTubeMetadata metaData, CancellationToken cancellationToken)
{
// download base.js
var client = HttpHelper.CreateClient();
using var response = await client.GetAsync(embedPageData.BaseJsUri, cancellationToken);
var scriptContent = await response.Content.ReadAsStringAsync();
var script = new YouTubeScript(scriptContent);
// find decipher function name
var match = DecipherFunctionRegex.Match(scriptContent);
if (!match.Success)
{
throw new GrabParseException("Failed to locate decipher function.");
}
var fn = match.Groups[1].Value;
// prepare script host to execute the decipher function along with its used functions
script.PrepareDecipherFunctionCall(fn);
// call decipher function
foreach (var streamInfo in metaData.AllStreams)
{
if (string.IsNullOrEmpty(streamInfo.Signature))
{
continue;
}
// calculate decipher
streamInfo.Decipher = script.CallDecipherFunction(fn, streamInfo.Signature);
// update uri
streamInfo.Url += $"&sig={Uri.EscapeDataString(streamInfo.Decipher)}";
}
}