perf: prefer VideoToolbox decoding with software fallback

2026-10-17 01:11:58 +02:00
parent 599c1492ee
commit fcad96de62
8 changed files with 513 additions and 36 deletions
@@ -0,0 +1,74 @@
+#pragma once
+#include <algorithm>
+extern "C" {
+#include <libavcodec/avcodec.h>
+#include <libavutil/hwcontext.h>
+}
+
+namespace playback {
+inline bool hasIDR(const AVPacket &packet, const AVCodecParameters &codec) {
+    const auto *bytes = packet.data;
+    const size_t size = size_t(std::max(0, packet.size));
+    if (codec.extradata_size >= 5 && codec.extradata[0] == 1) {
+        const size_t lengthSize = (codec.extradata[4] & 3) + 1;
+        for (size_t at = 0; at + lengthSize <= size;) {
+            uint32_t length = 0;
+            for (size_t i = 0; i < lengthSize; ++i) length = (length << 8) | bytes[at++];
+            if (!length || length > size - at) return false;
+            if ((bytes[at] & 31) == 5) return true;
+            at += length;
+        }
+        return false;
+    }
+    for (size_t at = 0; at + 3 < size; ++at) {
+        if (bytes[at] == 0 && bytes[at + 1] == 0 && bytes[at + 2] == 1 &&
+            (bytes[at + 3] & 31) == 5) return true;
+    }
+    return false;
+}
+// FFmpeg retries software if VideoToolbox rejects the stream; HEVC may also use
+// Apple's platform software fallback. Keep the normal decoder for other codecs.
+static inline void preferVideoToolbox(AVCodecContext *context) {
+#ifndef TEREBI_SOFTWARE_DECODE
+    // Prefer only the codecs measured in native playback and the Cast relay.
+    if (context->codec_id != AV_CODEC_ID_H264 && context->codec_id != AV_CODEC_ID_HEVC &&
+        context->codec_id != AV_CODEC_ID_VP9) return;
+    for (int index = 0; const auto *config = avcodec_get_hw_config(context->codec, index); ++index) {
+        if (config->device_type != AV_HWDEVICE_TYPE_VIDEOTOOLBOX ||
+            !(config->methods & AV_CODEC_HW_CONFIG_METHOD_HW_DEVICE_CTX)) continue;
+        // The default get_format prefers this device and retries software if
+        // VideoToolbox rejects the stream; device creation failure is also safe.
+        av_hwdevice_ctx_create(&context->hw_device_ctx, AV_HWDEVICE_TYPE_VIDEOTOOLBOX,
+                               nullptr, nullptr, 0);
+        break;
+    }
+#endif
+}
+// Starting at a dependent packet can make VideoToolbox fail during send_packet,
+// after format negotiation has already succeeded. Preserve software preroll.
+inline bool independentVideoPacket(const AVPacket &packet, const AVCodecParameters &parameters) {
+    return (packet.flags & AV_PKT_FLAG_KEY) &&
+        (parameters.codec_id != AV_CODEC_ID_H264 || hasIDR(packet, parameters));
+}
+inline int prepareVideoPacket(AVCodecContext *&context, const AVCodecParameters &parameters,
+                              const AVPacket &packet) {
+    if (!context->hw_device_ctx || independentVideoPacket(packet, parameters)) return 0;
+    auto *software = avcodec_alloc_context3(context->codec);
+    if (!software) return AVERROR(ENOMEM);
+    int result = avcodec_parameters_to_context(software, &parameters);
+    software->pkt_timebase = context->pkt_timebase;
+    software->thread_count = context->thread_count;
+    software->max_pixels = context->max_pixels;
+    if (result >= 0) result = avcodec_open2(software, context->codec, nullptr);
+    if (result < 0) { avcodec_free_context(&software); return result; }
+    avcodec_free_context(&context); context = software;
+    return 0;
+}
+// Mapping retains and locks the CVPixelBuffer until the last frame reference
+// is released. Consumers see ordinary CPU-readable planes without a pixel copy.
+inline int refVideoFrame(AVFrame *destination, const AVFrame *source) {
+    if (source->format == AV_PIX_FMT_VIDEOTOOLBOX)
+        return av_hwframe_map(destination, source, AV_HWFRAME_MAP_READ);
+    return av_frame_ref(destination, source);
+}
+}