[FFmpeg-devel] [PATCH 8/9] avcodec/videotoolbox: use decode_params to propagate PPS changes and restart on SPS changes

[Aman Gupta]

From: Aman Gupta <aman at tmm1.net>

If the VideoToolbox session needs to be restarted, and
videotoolbox_start() fails for some reason (for instance, if the video
is interlaced and the decoder is running on iOS), avcodec will return
AVERROR_EXTERNAL. This can be used by the API user to switch to another
decoder.
---
 libavcodec/vda_vt_internal.h |  6 ++++++
 libavcodec/videotoolbox.c    | 45 +++++++++++++++++++++++++++++++++++++++++++-
 2 files changed, 50 insertions(+), 1 deletion(-)

diff --git a/libavcodec/vda_vt_internal.h b/libavcodec/vda_vt_internal.h
index e55a813899..49c91791ee 100644
--- a/libavcodec/vda_vt_internal.h
+++ b/libavcodec/vda_vt_internal.h
@@ -47,6 +47,12 @@ typedef struct VTContext {
     // Non-NULL if the new hwaccel API is used. This is only a separate struct
     // to ease compatibility with the old API.
     struct AVVideotoolboxContext *vt_ctx;
+
+    // Current H264 parameters (used to trigger decoder restart on SPS changes).
+    uint8_t                     *sps;
+    uint32_t                    sps_len;
+    unsigned int                sps_capa;
+    bool                        reconfig_needed;
 } VTContext;
 
 int ff_videotoolbox_alloc_frame(AVCodecContext *avctx, AVFrame *frame);
diff --git a/libavcodec/videotoolbox.c b/libavcodec/videotoolbox.c
index f56ab1f8c9..6c8477c2ce 100644
--- a/libavcodec/videotoolbox.c
+++ b/libavcodec/videotoolbox.c
@@ -41,6 +41,9 @@
 
 #define VIDEOTOOLBOX_ESDS_EXTRADATA_PADDING  12
 
+static void videotoolbox_stop(AVCodecContext *avctx);
+static int videotoolbox_start(AVCodecContext *avctx);
+
 static void videotoolbox_buffer_release(void *opaque, uint8_t *data)
 {
     CVPixelBufferRef cv_buffer = (CVImageBufferRef)data;
@@ -148,6 +151,33 @@ int ff_videotoolbox_h264_start_frame(AVCodecContext *avctx,
     return 0;
 }
 
+static int videotoolbox_h264_decode_params(AVCodecContext *avctx,
+                                           const uint8_t *buffer,
+                                           uint32_t size)
+{
+    VTContext *vtctx = avctx->internal->hwaccel_priv_data;
+    H264Context *h  = avctx->priv_data;
+
+    if (h->is_avc == 1)
+        return 0;
+
+    switch (buffer[0] & 0x1f) {
+        case H264_NAL_SPS:
+            if (!vtctx->sps || vtctx->sps_len != size || memcmp(buffer, vtctx->sps, size) != 0) {
+                vtctx->sps = av_fast_realloc(vtctx->sps, &vtctx->sps_capa, size);
+                if (vtctx->sps)
+                    memcpy(vtctx->sps, buffer, size);
+                if (vtctx->sps_len)
+                    vtctx->reconfig_needed = true;
+                vtctx->sps_len = size;
+            }
+            break;
+    }
+
+    // pass-through new PPS to the decoder
+    return ff_videotoolbox_h264_decode_slice(avctx, buffer, size);
+}
+
 int ff_videotoolbox_h264_decode_slice(AVCodecContext *avctx,
                                       const uint8_t *buffer,
                                       uint32_t size)
@@ -180,6 +210,7 @@ int ff_videotoolbox_uninit(AVCodecContext *avctx)
     VTContext *vtctx = avctx->internal->hwaccel_priv_data;
     if (vtctx) {
         av_freep(&vtctx->bitstream);
+        av_freep(&vtctx->sps);
         if (vtctx->frame)
             CVPixelBufferRelease(vtctx->frame);
     }
@@ -419,7 +450,16 @@ static int videotoolbox_common_end_frame(AVCodecContext *avctx, AVFrame *frame)
     AVVideotoolboxContext *videotoolbox = videotoolbox_get_context(avctx);
     VTContext *vtctx = avctx->internal->hwaccel_priv_data;
 
-    if (!videotoolbox->session || !vtctx->bitstream)
+    if (vtctx->reconfig_needed == true) {
+        vtctx->reconfig_needed = false;
+        av_log(avctx, AV_LOG_VERBOSE, "VideoToolbox decoder needs reconfig, restarting..\n");
+        videotoolbox_stop(avctx);
+        if (videotoolbox_start(avctx) != 0) {
+            return AVERROR_EXTERNAL;
+        }
+    }
+
+    if (!videotoolbox->session || !vtctx->bitstream || !vtctx->bitstream_size)
         return AVERROR_INVALIDDATA;
 
     status = videotoolbox_session_decode_frame(avctx);
@@ -432,9 +472,11 @@ static int videotoolbox_common_end_frame(AVCodecContext *avctx, AVFrame *frame)
                 break;
             case kVTVideoDecoderMalfunctionErr:
                 error = "decoder malfunction";
+                vtctx->reconfig_needed = true;
                 break;
             case kVTInvalidSessionErr:
                 error = "invalid session";
+                vtctx->reconfig_needed = true;
                 break;
             default:
                 error = "unknown";
@@ -824,6 +866,7 @@ AVHWAccel ff_h264_videotoolbox_hwaccel = {
     .alloc_frame    = ff_videotoolbox_alloc_frame,
     .start_frame    = ff_videotoolbox_h264_start_frame,
     .decode_slice   = ff_videotoolbox_h264_decode_slice,
+    .decode_params  = videotoolbox_h264_decode_params,
     .end_frame      = videotoolbox_h264_end_frame,
     .init           = videotoolbox_common_init,
     .uninit         = videotoolbox_uninit,
-- 
2.13.5 (Apple Git-94)