Motown: New wrapper classes for ffmpeg format context and io context

services/media/framework_ffmpeg/av_io_context.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/parts/reader.h"
+#include "services/media/framework_ffmpeg/av_io_context.h"
+#include "services/media/framework_ffmpeg/ffmpeg_init.h"
+extern "C" {
+#include "third_party/ffmpeg/libavformat/avio.h"
+}
+
+namespace mojo {
+namespace media {
+
+void AVIOContextDeleter::operator()(AVIOContext* context) const {
+  AvIoContext* av_io_context = reinterpret_cast<AvIoContext*>(context->opaque);
+  DCHECK(av_io_context);
+  delete av_io_context;
+  av_free(context->buffer);
+  av_free(context);
+}
+
+// static
+AvIoContextPtr AvIoContext::Create(std::shared_ptr<Reader> reader) {
+  // Internal buffer size used by AVIO for reading.
+  const int kBufferSize = 32 * 1024;

[johngro, 2016/03/21 21:06:08]

constexpr

+
+  InitFfmpeg();

[johngro, 2016/03/21 21:06:08]

your other FFmpeg helper classes/structs seem to make the assumption that FFmpeg
has already been initialized by the environment, AvIoContext probably should as
well.

If you have a IsFfmpegInited() function somewhere (or one is easy to write), it
might be a good idea to DCHECK that in all of these cases.

[dalesat, 2016/03/22 00:31:35]

Done.

+
+  AVIOContext* result = avio_alloc_context(
+      static_cast<unsigned char*>(av_malloc(kBufferSize)),
+      kBufferSize,
+      0, // write_flag
+      new AvIoContext(reader),
+      &Read,
+      nullptr,
+      &Seek);
+
+  // Ensure FFmpeg only tries to seek when we know how.
+  result->seekable = reader->CanSeek() ? AVIO_SEEKABLE_NORMAL : 0;
+
+  // Ensure writing is disabled.
+  result->write_flag = 0;
+
+  return AvIoContextPtr(result);
+}
+
+// static
+int AvIoContext::Read(void* opaque, uint8_t* buf, int buf_size) {
+  AvIoContext* av_io_context = reinterpret_cast<AvIoContext*>(opaque);
+  return av_io_context->Read(buf, buf_size);
+}
+
+// static
+int64_t AvIoContext::Seek(void* opaque, int64_t offset, int whence) {
+  AvIoContext* av_io_context = reinterpret_cast<AvIoContext*>(opaque);
+  return av_io_context->Seek(offset, whence);
+}
+
+AvIoContext::~AvIoContext() {}
+
+AvIoContext::AvIoContext(std::shared_ptr<Reader> reader) : reader_(reader) {
+  can_seek_ = reader_->CanSeek();
+
+  size_t size = reader_->GetSize();
+  DCHECK(size <= std::numeric_limits<int64_t>::max());

[johngro, 2016/03/21 21:06:08]

this DCHECK can never fail, so its probably OK to just drop it.

[dalesat, 2016/03/22 00:31:35]

Done.

+  size_ = size == Reader::kFailed ? -1 : static_cast<int>(size);
+}
+
+int AvIoContext::Read(uint8_t* buffer, size_t bytes_to_read) {
+  size_t bytes_read = reader_->Read(buffer, bytes_to_read);
+  if (bytes_read == Reader::kFailed) {
+    return AVERROR(EIO);
+  }
+  position_ += bytes_read;
+  return bytes_read;
+}
+
+int64_t AvIoContext::Seek(int64_t offset, int whence) {
+  if (whence == AVSEEK_SIZE) {
+    if (size_ == -1) {
+      return AVERROR(EIO);
+    }
+    return size_;
+  }
+
+  switch (whence) {
+    case SEEK_SET:
+      position_ = offset;
+      return position_;
+    case SEEK_CUR:
+      position_ += offset;
+      return position_;
+    case SEEK_END:
+      if (size_ == -1) {
+        return AVERROR(EIO);
+      }
+      position_ = size_ + offset;
+      return position_;
+    case AVSEEK_SIZE:
+      if (size_ == -1) {
+        return AVERROR(EIO);
+      }
+      return size_;
+    default:
+      NOTREACHED();
+      return AVERROR(EIO);
+  }
+
+  CHECK(size_ == -1 || position_ < size_) << "position out of range";
+  return position_;
+}
+
+
+} // namespace media
+} // namespace mojo