Expondo vídeo através do ASP.NET Web API

Além de possibilitar o retorno de tipos mais simples, tais como inteiros, strings e também de objetos que representam o nosso negócio (Produto, Pedido, Cliente, etc.), o ASP.NET Web API também é capaz de retornar outros tipos de recursos, tais como vídeos ou músicas, permitindo ao cliente ir consumindo o mesmo sob demanda, ou seja, na medida em que ele vai tocando, o conteúdo vai sendo baixado, sem a necessidade de trazer todo o conteúdo antes de utilizar. Isso garantirá ao cliente ouvir/assistir e decidir abortar sem a necessidade de realizar o download completo do arquivo, que muitas vezes é grande.

Para este tipo de cenário temos a classe PushStreamContent. Essa classe herda de HttpContent e, consequentemente, pode ser definida como o conteúdo da mensagem de resposta. Essa classe permite estabelecer a comunicação entre o serviço e o cliente através de um stream, que ao serem escritas informações nele, viajará até o cliente para que ele decida o que fazer com o mesmo. O construtor desta classe permite a iniciliazação através de um delegate do tipo Func<>, que entre os parâmetros que são fornecidos, um deles é justamente o stream que liga o cliente ao serviço.

Ao utilizar este stream, o conteúdo será encaminhado ao cliente diretamente. Para o exemplo, vamos permitir ao cliente informar o nome do vídeo que ele deseja assistir, e o serviço será responsável por extrair este arquivo do disco, particionar os bytes do arquivo (através de um buffer de 5 MB), e dentro do laço while, ele vai enviando estes “pedaços” ao cliente de forma assíncrona. Abaixo está o controller completo com esta funcionalidade.

public class EntretenimentoController : ApiController
    private const int TamanhoDoBuffer = 1024 * 32;
    private readonly string Diretorio;

    public EntretenimentoController()
        this.Diretorio = HttpContext.Current.Server.MapPath(“~/App_Data”);

    public HttpResponseMessage BuscarVideo(string nomeDoVideo)
        return new HttpResponseMessage(HttpStatusCode.OK)
            Content = new PushStreamContent(
                async (stream, content, context) =>
                    await ExtrairRecurso(Path.Combine(Diretorio, nomeDoVideo), stream), “video/mp4”)

    private static async Task ExtrairRecurso(string fileName, Stream output)
        var buffer = new byte[TamanhoDoBuffer];
        var read = 0;

        using (var input = File.OpenRead(fileName))
            while ((read = input.Read(buffer, 0, TamanhoDoBuffer)) > 0)
                await output.WriteAsync(buffer, 0, read);

O consumo do vídeo pode ser realizado através dos novos recursos do HTML 5, que através da tag <video /> permite associar uma URL que produz o conteúdo, fazendo o trabalho de acumular e ir exibindo o vídeo que está sendo retornado. O código abaixo ilustra como embutir o player no HTML:

<!DOCTYPE html>
<html xmlns=”http://www.w3.org/1999/xhtml”&gt;
    <video width=”480″ height=”320″ controls=”controls” autoplay=”autoplay”>
        <source src=”/api/Entretenimento/BuscarVideo?nomeDoVideo=TranneNoi.mp4″

Por fim, para conseguir perceber o resultado, a imagem abaixo (clique para ampliar) ilustra de um lado o Visual Studio com o breakpoint parado no interior do while, e apesar de não perceber isso na imagem (porque ela é estática), o vídeo também está parado esperando que se escreva mais bytes no stream para que ele possa exibir, e na medida em que se passa pelo loop, logo o vídeo volta a ser executado até que, obviamente, pare de receber novamente os bytes ou quando o mesmo já estiver encerrado.

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