WebP example

[trong]

I use the following CLI-command to get webp image (screenshot):

ffmpeg -i video.ts -ss 00:00:00.100 -vframes 1 screen.webp

I tried to modify video-to-jpeg.go, but in result I got empty files with .webp extensions (if I use gmf.AV_PIX_FMT_RGB32) or error ... :

[libwebp_anim @ 0x709da00] Specified pixel format argb is invalid or not supported
2016/05/12 18:38:30 Error opening codec 'libwebp_anim:libwebp WebP image', averror: Invalid argument

... if I use gmf.AV_PIX_FMT_ARGB

Code:

package main

import (
    "log"
    "os"
    "strconv"

    "github.com/3d0c/gmf"
)

func assert(i interface{}, err error) interface{} {
    if err != nil {
        log.Fatal(err)
    }

    return i
}

var i int = 0

func writeFile(b []byte) {
    name := strconv.Itoa(i) + ".webp"

    fp, err := os.Create(name)
    if err != nil {
        log.Fatal(err)
    }

    defer func() {
        if err := fp.Close(); err != nil {
            log.Fatal(err)
        }
        i++
    }()

    if n, err := fp.Write(b); err != nil {
        log.Fatal(err)
    } else {
        log.Println(n, "bytes written to", name)
    }
}

func main() {
    srcFileName := "video.ts"

    inputCtx := assert(gmf.NewInputCtx(srcFileName)).(*gmf.FmtCtx)
    defer inputCtx.CloseInputAndRelease()

    srcVideoStream, err := inputCtx.GetBestStream(gmf.AVMEDIA_TYPE_VIDEO)
    if err != nil {
        log.Println("No video stream found in", srcFileName)
    }

    codec, err := gmf.FindEncoder(gmf.AV_CODEC_ID_WEBP)
    if err != nil {
        log.Fatal(err)
    }

    cc := gmf.NewCodecCtx(codec)
    defer gmf.Release(cc)

    cc.SetPixFmt(gmf.AV_PIX_FMT_ARGB).SetWidth(srcVideoStream.CodecCtx().Width()).SetHeight(srcVideoStream.CodecCtx().Height())

    if codec.IsExperimental() {
        cc.SetStrictCompliance(gmf.FF_COMPLIANCE_EXPERIMENTAL)
    }

    if err := cc.Open(nil); err != nil {
        log.Fatal(err)
    }

    swsCtx := gmf.NewSwsCtx(srcVideoStream.CodecCtx(), cc, gmf.SWS_BICUBIC)
    defer gmf.Release(swsCtx)

    dstFrame := gmf.NewFrame().SetWidth(srcVideoStream.CodecCtx().Width()).SetHeight(srcVideoStream.CodecCtx().Height()).SetFormat(gmf.AV_PIX_FMT_ARGB)
    defer gmf.Release(dstFrame)

    if err := dstFrame.ImgAlloc(); err != nil {
        log.Fatal(err)
    }

    for packet := range inputCtx.GetNewPackets() {
        if packet.StreamIndex() != srcVideoStream.Index() {
            // skip non video streams
            continue
        }
        ist := assert(inputCtx.GetStream(packet.StreamIndex())).(*gmf.Stream)

        for frame := range packet.Frames(ist.CodecCtx()) {
            swsCtx.Scale(frame, dstFrame)

            if p, ready, _ := dstFrame.EncodeNewPacket(cc); ready {
                writeFile(p.Data())
                defer gmf.Release(p)
            }
        }
        gmf.Release(packet)
    }

    gmf.Release(dstFrame)
}

Could you say how to do it right?