Motown: ffmpeg implementations of framework 'parts'

services/media/framework_ffmpeg/ffmpeg_audio_decoder.cc

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "base/logging.h"
+#include "services/media/framework_ffmpeg/ffmpeg_audio_decoder.h"
+
+namespace mojo {
+namespace media {
+
+FfmpegAudioDecoder::FfmpegAudioDecoder(AvCodecContextPtr av_codec_context) :
+    FfmpegDecoderBase(std::move(av_codec_context)) {
+  DCHECK(context());
+  DCHECK(context()->channels > 0);
+
+  context()->opaque = this;
+  context()->get_buffer2 = AllocateBufferForAvFrame;
+  context()->refcounted_frames = 1;
+
+  if (av_sample_fmt_is_planar(context()->sample_fmt)) {
+    // Prepare for interleaving.
+    stream_type_ = output_stream_type();
+    lpcm_util_ = LpcmUtil::Create(*stream_type_->lpcm());
+  }
+}
+
+FfmpegAudioDecoder::~FfmpegAudioDecoder() {}
+
+int FfmpegAudioDecoder::Decode(
+    PayloadAllocator* allocator,
+    bool* frame_decoded_out) {
+  DCHECK(allocator);
+  DCHECK(frame_decoded_out);
+  DCHECK(context());
+  DCHECK(frame());
+
+  // Use the provided allocator (for allocations in AllocateBufferForAvFrame)
+  // unless we intend to interleave later, in which case use the default
+  // allocator. We'll interleave into a buffer from the provided allocator
+  // in CreateOutputPacket.
+  allocator_ = lpcm_util_ ? PayloadAllocator::GetDefault() : allocator;
+
+  int frame_decoded = 0;
+  int input_bytes_used = avcodec_decode_audio4(
+      context().get(),
+      frame().get(),
+      &frame_decoded,
+      &packet());
+  *frame_decoded_out = frame_decoded != 0;
+
+  // We're done with this allocator.
+  allocator_ = nullptr;
+
+  return input_bytes_used;
+}
+
+PacketPtr FfmpegAudioDecoder::CreateOutputPacket(PayloadAllocator* allocator) {
+  DCHECK(allocator);
+  DCHECK(frame());
+
+  int64_t presentation_time = frame()->pts;
+  if (presentation_time == AV_NOPTS_VALUE) {
+    // TODO(dalesat): Adjust next_presentation_time_ for seek/non-zero start.
+    presentation_time = next_presentation_time_;
+    next_presentation_time_ += frame()->nb_samples;
+  }
+
+  uint64_t payload_size;
+  void *payload_buffer;
+
+  AvBufferContext* av_buffer_context =
+      reinterpret_cast<AvBufferContext*>(av_buffer_get_opaque(frame()->buf[0]));
+
+  if (lpcm_util_) {
+    // We need to interleave. The non-interleaved frames are in a buffer that
+    // was allocated from the default allocator. That buffer will get released
+    // later in ReleaseBufferForAvFrame. We need a new buffer for the
+    // interleaved frames, which we get from the provided allocator.
+    DCHECK(stream_type_);
+    DCHECK(stream_type_->lpcm());
+    payload_size = stream_type_->lpcm()->min_buffer_size(frame()->nb_samples);
+    payload_buffer = allocator->AllocatePayloadBuffer(payload_size);
+
+    lpcm_util_->Interleave(
+        av_buffer_context->buffer(),
+        av_buffer_context->size(),
+        payload_buffer,
+        frame()->nb_samples);
+  } else {
+    // We don't need to interleave. The interleaved frames are in a buffer that
+    // was allocated from the correct allocator. We take ownership of the buffer
+    // by calling Release here so that ReleaseBufferForAvFrame won't release it.
+    payload_size = av_buffer_context->size();
+    payload_buffer = av_buffer_context->Release();
+  }
+
+  return Packet::Create(
+      presentation_time,
+      frame()->nb_samples,
+      false, // The base class is responsible for end-of-stream.
+      payload_size,
+      payload_buffer,
+      allocator);
+}
+
+PacketPtr FfmpegAudioDecoder::CreateOutputEndOfStreamPacket() {
+  return Packet::CreateEndOfStream(next_presentation_time_);
+}
+
+int FfmpegAudioDecoder::AllocateBufferForAvFrame(
+    AVCodecContext* av_codec_context,
+    AVFrame* av_frame,
+    int flags) {
+  // CODEC_CAP_DR1 is required in order to do allocation this way.
+  DCHECK(av_codec_context->codec->capabilities & CODEC_CAP_DR1);
+
+  FfmpegAudioDecoder* self =
+      reinterpret_cast<FfmpegAudioDecoder*>(av_codec_context->opaque);
+  DCHECK(self);
+  DCHECK(self->allocator_);
+
+  AVSampleFormat av_sample_format =
+      static_cast<AVSampleFormat>(av_frame->format);
+
+  int buffer_size = av_samples_get_buffer_size(
+      &av_frame->linesize[0],
+      av_codec_context->channels,
+      av_frame->nb_samples,
+      av_sample_format,
+      FfmpegAudioDecoder::kChannelAlign);
+  if (buffer_size < 0) {
+    LOG(WARNING) << "av_samples_get_buffer_size failed";
+    return buffer_size;
+  }
+
+  AvBufferContext* av_buffer_context =
+      new AvBufferContext(buffer_size, self->allocator_);
+  uint8_t* buffer = av_buffer_context->buffer();
+
+  if (!av_sample_fmt_is_planar(av_sample_format)) {
+    // Samples are interleaved. There's just one buffer.
+    av_frame->data[0] = buffer;
+  } else {
+    // Samples are not interleaved. There's one buffer per channel.
+    int channels = av_codec_context->channels;
+    int bytes_per_channel = buffer_size / channels;
+    uint8_t* channel_buffer = buffer;
+
+    DCHECK(buffer != nullptr || bytes_per_channel == 0);
+
+    if (channels <= AV_NUM_DATA_POINTERS) {
+      // The buffer pointers will fit in av_frame->data.
+      DCHECK_EQ(av_frame->extended_data, av_frame->data);
+      for (int channel = 0; channel < channels; ++channel) {
+        av_frame->data[channel] = channel_buffer;
+        channel_buffer += bytes_per_channel;
+      }
+    } else {
+      // Too many channels for av_frame->data. We have to use
+      // av_frame->extended_data
+      av_frame->extended_data = static_cast<uint8_t**>(
+          av_malloc(channels * sizeof(*av_frame->extended_data)));
+
+      // The first AV_NUM_DATA_POINTERS go in both data and extended_data.
+      int channel = 0;
+      for (; channel < AV_NUM_DATA_POINTERS; ++channel) {
+        av_frame->extended_data[channel] = av_frame->data[channel] =
+            channel_buffer;
+        channel_buffer += bytes_per_channel;
+      }
+
+      // The rest go only in extended_data.
+      for (; channel < channels; ++channel) {
+        av_frame->extended_data[channel] = channel_buffer;
+        channel_buffer += bytes_per_channel;
+      }
+    }
+  }
+
+  av_frame->buf[0] = av_buffer_create(
+      buffer,
+      buffer_size,
+      ReleaseBufferForAvFrame,
+      av_buffer_context,
+      0); // flags
+
+  return 0;
+}
+
+void FfmpegAudioDecoder::ReleaseBufferForAvFrame(
+    void* opaque,
+    uint8_t* buffer) {
+  AvBufferContext* av_buffer_context =
+      reinterpret_cast<AvBufferContext*>(opaque);
+  DCHECK(av_buffer_context);
+  // Either this buffer has already been released to someone else's ownership,
+  // or it's the same as the buffer parameter.

[johngro, 2016/03/03 23:03:16]

this still makes me vaguely uneasy...  The FFmpeg frame is still holding a
pointer to the buffer which once lived in the av_buffer_context but may have
been detached.

The safety of all of this depends on being certain that after we detach the
buffer from the context, that the FFmpeg never makes any more attempts to do
anything with the frame which still has a copy of the buffer pointer.

In this case, we should have this guarantee, because
FfmpegDecoderBase::PacketFromAvFrame is going to call av_frame_unref immediately
following the call to CreateOutputPacket; but this is not immediately obvious at
the point that we detach the buffer from the buffer context (line 94 above).

Another way to approch this might have been to actually go into the AVFrame
structure and null out the release hook, the release hook context, and the
buffer/length pointers in the frame->buf[*] members if you take ownership of the
memory back from the frame.  Then, no matter what happens with the frame from
there on out, it will not be able to touch the memory you have taken back from
it.  It has the added benefit of eliminating the need to heap allocate the
context structure for each frame

I don't want to hold this up any longer.  I'm going to open an issue to track my
uneasy-ness which I will CC you on.  We can get this in and come back later to
clean up the ownership interactions with FFmpeg.

+  DCHECK(
+      av_buffer_context->buffer() == nullptr ||
+      av_buffer_context->buffer() == buffer);
+  delete av_buffer_context;
+}
+
+} // namespace media
+} // namespace mojo