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如何使用 ffmpeg 解码具有硬件加速的文件？

我编写了一个使用 ffmpeg 的工作视频播放器。我已经检查了使用"av_hwaccel_next"并找到了支持mpeg2_dxva。

但是，当我加载一个 mpeg2 文件（像往常一样）时，我没有得到任何硬件加速。AVCodecContext->hwaccel并且AVCodecContext->hwaccelcontext都是空的。

我是否必须在某处传递一些标志才能启用硬件加速？

我一直无法找到有关此的任何信息，有人知道好的来源吗？

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1 回答 1

27

从阅读 ffmpeg 文档开始：https ://trac.ffmpeg.org/wiki/HWAccelIntro和更好的答案How to use hardware acceleration with ffmpeg (and for linux check page https://wiki.archlinux.org/index.php/Hardware_video_acceleration )

使用 FFmpeg 工具时，通过-hwaccel启用特定解码器的选项启用硬件辅助解码。每个解码器可能有特定的限制（例如，H.264 解码器可能只支持基线配置文件）。通过使用特定编码器（例如 h264_nvenc）启用硬件辅助编码。过滤硬件辅助处理仅在少数过滤器中支持.. 有几种硬件加速标准 API，其中一些在某种程度上被 FFmpeg 支持。

hwaccel 激活由代码控制（2013 年之后重新格式化的位https://github.com/FFmpeg/FFmpeg/commit/08303d774132775d49d4ba767092de5d426f089d）

avctx->hwaccel = ff_find_hwaccel(avctx->codec->id, avctx->pix_fmt);

例如在 libavcodec/mpeg12dec.c https://github.com/FFmpeg/FFmpeg/blob/6c7254722ad43712db5686feee8bf75c74d8635b/libavcodec/mpeg12dec.c

avctx->pix_fmt = mpeg_get_pixelformat(avctx);
avctx->hwaccel = ff_find_hwaccel(avctx->codec->id, avctx->pix_fmt);

检查图像的ff_find_hwaccel编解码器和像素格式对以及所有可用的加速器。

AVHWAccel *ff_find_hwaccel(enum CodecID codec_id, enum PixelFormat pix_fmt)
{
    AVHWAccel *hwaccel=NULL;

    while((hwaccel= av_hwaccel_next(hwaccel))){
        if (   hwaccel->id      == codec_id
            && hwaccel->pix_fmt == pix_fmt)
            return hwaccel;
    }
    return NULL;
}

例如，dxva2 ( https://en.wikipedia.org/wiki/DirectX_Video_Acceleration ) 有：

AVHWAccel mpeg2_dxva2_hwaccel = {
    .name           = "mpeg2_dxva2",
    .type           = AVMEDIA_TYPE_VIDEO,
    .id             = CODEC_ID_MPEG2VIDEO,
    .pix_fmt        = PIX_FMT_DXVA2_VLD,
    .capabilities   = 0,
    .start_frame    = start_frame,
    .decode_slice   = decode_slice,
    .end_frame      = end_frame,
    .priv_data_size = sizeof(struct dxva2_picture_context),
};

并按libavutil/pixfmt.h像素格式列出所有支持的硬件解码器/加速器https://ffmpeg.org/doxygen/3.2/pixfmt_8h.html

AV_PIX_FMT_XVMC_MPEG2_MC    - XVideo Motion Acceleration via common packet passing.
AV_PIX_FMT_XVMC_MPEG2_IDCT  - undocumented
AV_PIX_FMT_XVMC         - undocumented
AV_PIX_FMT_VDPAU_H264   - H.264 HW decoding with VDPAU, data[0] contains a vdpau_render_state struct which contains the bitstream of the slices as well as various fields extracted from headers.
AV_PIX_FMT_VDPAU_MPEG1  - MPEG-1 HW decoding with VDPAU, data[0] contains a vdpau_render_state struct which contains the bitstream of the slices as well as various fields extracted from headers.
AV_PIX_FMT_VDPAU_MPEG2  - MPEG-2 HW decoding with VDPAU, data[0] contains a vdpau_render_state struct which contains the bitstream of the slices as well as various fields extracted from headers.
AV_PIX_FMT_VDPAU_WMV3   - WMV3 HW decoding with VDPAU, data[0] contains a vdpau_render_state struct which contains the bitstream of the slices as well as various fields extracted from headers.
AV_PIX_FMT_VDPAU_VC1    - VC-1 HW decoding with VDPAU, data[0] contains a vdpau_render_state struct which contains the bitstream of the slices as well as various fields extracted from headers. 
AV_PIX_FMT_VAAPI_MOCO   - HW acceleration through VA API at motion compensation entry-point, Picture.data[3] contains a vaapi_render_state struct which contains macroblocks as well as various fields extracted from headers.
AV_PIX_FMT_VAAPI_IDCT   - HW acceleration through VA API at IDCT entry-point, Picture.data[3] contains a vaapi_render_state struct which contains fields extracted from headers.
AV_PIX_FMT_VAAPI_VLD    - HW decoding through VA API, Picture.data[3] contains a VASurfaceID. 
AV_PIX_FMT_VDPAU_MPEG4  - MPEG-4 HW decoding with VDPAU, data[0] contains a vdpau_render_state struct which contains the bitstream of the slices as well as various fields extracted from headers.
AV_PIX_FMT_DXVA2_VLD    - HW decoding through DXVA2, Picture.data[3] contains a LPDIRECT3DSURFACE9 pointer. 
AV_PIX_FMT_VDPAU        - HW acceleration through VDPAU, Picture.data[3] contains a VdpVideoSurface. 
AV_PIX_FMT_VDA          - HW acceleration through VDA, data[3] contains a CVPixelBufferRef. 
AV_PIX_FMT_QSV          - HW acceleration through QSV, data[3] contains a pointer to the mfxFrameSurface1 structure.
AV_PIX_FMT_MMAL         - HW acceleration though MMAL, data[3] contains a pointer to the MMAL_BUFFER_HEADER_T structure.
AV_PIX_FMT_D3D11VA_VLD  - HW decoding through Direct3D11, Picture.data[3] contains a ID3D11VideoDecoderOutputView pointer.
AV_PIX_FMT_CUDA         - HW acceleration through CUDA. data[i] contain CUdeviceptr pointers exactly as for system memory frames.

像素格式的实际选择是在之前调用的函数中，ff_find_hwaccel对于mpeg1/2。在 ffmpeg/libavcodec 的早期版本中，它在某些情况下会检查和/或调用以启用硬件解码。static enum PixelFormat mpeg_get_pixelformat(AVCodecContext *avctx)libavcodec/mpeg12dec.cavctx->xvmc_accelerationavctx->codec->capabilities&CODEC_CAP_HWACCEL_VDPAUavctx->get_format(avctx,ff_hwaccel_pixfmt_list_420);

在最近的版本（2017）中，它和附近的几个函数选择了硬件编码器https://github.com/FFmpeg/FFmpeg/blob/aff8cf18cb0b1fa4f2e3d163c3da2f25aa6d1906/libavcodec/mpeg12dec.c#L1189。

基本上：硬件解码器及其 api（过时的XVMC、VDPAU、VA API、MS DXVA或 MS Direct3D11或 videotoolbox）应在您的 ffmpeg 构建中启用，并由您的硬件及其驱动程序/库支持（许多是专有的，应该是单独下载）。-hwaccel有时应为 ffmpeg 或加载插件提供选项。在 linux 中，您可以使用vainfo和vdpauinfo命令来测试可用性和支持的配置文件以及最流行的标准视频硬件解码 API。

输入文件（对于 mpeg1/2）不应该是灰度，它应该s->chroma_format少于 2（4:2:0色度子采样，这对于 ISO/IEC MPEG 和 ITU-T VCEG H.26x 很常见；但对于某些 MPEG -4 第 2 部分，不适用于 H.264/MPEG-4 AVC 的高 4:4:4 变体）。

static const enum AVPixelFormat mpeg2_hwaccel_pixfmt_list_420[] = {
#if CONFIG_MPEG2_XVMC_HWACCEL
    AV_PIX_FMT_XVMC,
#endif
#if CONFIG_MPEG_VDPAU_DECODER && FF_API_VDPAU
    AV_PIX_FMT_VDPAU_MPEG2,
#endif
#if CONFIG_MPEG2_VDPAU_HWACCEL
    AV_PIX_FMT_VDPAU,
#endif
#if CONFIG_MPEG2_DXVA2_HWACCEL
    AV_PIX_FMT_DXVA2_VLD,
#endif
#if CONFIG_MPEG2_D3D11VA_HWACCEL
    AV_PIX_FMT_D3D11VA_VLD,
#endif
#if CONFIG_MPEG2_VAAPI_HWACCEL
    AV_PIX_FMT_VAAPI,
#endif
#if CONFIG_MPEG2_VIDEOTOOLBOX_HWACCEL
    AV_PIX_FMT_VIDEOTOOLBOX,
#endif
    AV_PIX_FMT_YUV420P,
    AV_PIX_FMT_NONE
};

static const enum AVPixelFormat mpeg12_pixfmt_list_422[] = {
    AV_PIX_FMT_YUV422P,
    AV_PIX_FMT_NONE
};

static const enum AVPixelFormat mpeg12_pixfmt_list_444[] = {
    AV_PIX_FMT_YUV444P,
    AV_PIX_FMT_NONE
};

#if FF_API_VDPAU
static inline int uses_vdpau(AVCodecContext *avctx) {
    return avctx->pix_fmt == AV_PIX_FMT_VDPAU_MPEG1 || avctx->pix_fmt == AV_PIX_FMT_VDPAU_MPEG2;
}
#endif

static enum AVPixelFormat mpeg_get_pixelformat(AVCodecContext *avctx)
{
    Mpeg1Context *s1  = avctx->priv_data;
    MpegEncContext *s = &s1->mpeg_enc_ctx;
    const enum AVPixelFormat *pix_fmts;

    if (CONFIG_GRAY && (avctx->flags & AV_CODEC_FLAG_GRAY))
        return AV_PIX_FMT_GRAY8;

    if (s->chroma_format < 2)
        pix_fmts = avctx->codec_id == AV_CODEC_ID_MPEG1VIDEO ?
                                mpeg1_hwaccel_pixfmt_list_420 :
                                mpeg2_hwaccel_pixfmt_list_420;
    else if (s->chroma_format == 2)
        pix_fmts = mpeg12_pixfmt_list_422;
    else
        pix_fmts = mpeg12_pixfmt_list_444;

    return ff_thread_get_format(avctx, pix_fmts);
}

static void setup_hwaccel_for_pixfmt(AVCodecContext *avctx)
{
    // until then pix_fmt may be changed right after codec init
    if (avctx->hwaccel
#if FF_API_VDPAU
        || uses_vdpau(avctx)
#endif
        )
        if (avctx->idct_algo == FF_IDCT_AUTO)
            avctx->idct_algo = FF_IDCT_SIMPLE;

    if (avctx->hwaccel && avctx->pix_fmt == AV_PIX_FMT_XVMC) {
        Mpeg1Context *s1 = avctx->priv_data;
        MpegEncContext *s = &s1->mpeg_enc_ctx;

        s->pack_pblocks = 1;
#if FF_API_XVMC
FF_DISABLE_DEPRECATION_WARNINGS
        avctx->xvmc_acceleration = 2;
FF_ENABLE_DEPRECATION_WARNINGS
#endif /* FF_API_XVMC */
    }
}
于 2011-05-13T02:46:33.220 回答